Talk:Alpha Centauri/Archive 1

Hello wonderful writers!

There is one page, the Alpha Centauri page, that is regarding the star system as a whole (general info about all three stars: Alpha Centauri A and B, and Proxima Centauri). The page links to separate detail pages for each of the three stars. The one detail page about Alpha Centauri A indicates a Solar Luminance of 1.519. The main Alpha Centauri star-system page, however, indicates 1.57. Do you know which is the correct Luminance for Alpha Centauri A?

Answer: 1.519 is the best figure, see http://www.eso.org/outreach/press-rel/pr-2003/pr-05-03.html

Thanks. Once again, these pages are great!

Tesseract 501@aol.com

Presumably whoever wrote the above header was being facetious. This article is repetative in the extreme - we get it, Alpha Centauri is a binary which along with Proxima Centauri forms a triple star system. How many times does this information have to be repeated? Jmdeur (talk) 20:18, 16 October 2009 (UTC)

'A' out of focus

'A' component in the picture titled "Apparent and real trajectory of B component relative to A component" does not lie on bigger axis of B's orbit. More precicely, "flat" orbit is ok, but "tilted" orbit, as we supposedly are seeing it from Earth, is not. Either there is a mistake, or "tilted" pic accounts for the fact that A is not stationary, but has much smaller elliptic orbit too. If it's true, then "flat" orbit needs fixing instead.

On the image A is 'stationary' - B's trajectory is relative to the static A. A being out of the apparent B's trajectory focus is correct.
The assumption that the 'tilted' (yes, still apparently elliptical) orbit of B should have A in it's focus is NOT correct.
An orthonormal transformation (simply: rotation) of the 'flat' elliptical orbit in 3D again produces ellipse, however it is NOT invariant to the focus: focus of the source ellipse is NOT transformed to focus of the destination ellipse.
A nice example is that for some rotations ellipse transforms to apparent circle, but its originally 2 focuses do not turn to the single circle center. It could happen only for the singular case when ellipse transforms to apparent abscissa (but even in this case focus can transform to variety of positions)
Please, also consider the axes and peaks of the 'flat' ellipse are NOT transformed to axes and peaks of the "tilted" ellipse.
Finally the shortest/longest year segment in the apparent orbit does not match with the shortest/longest year segment on the real orbit (you can check it easily).
Though it seems like the well known Kepler's laws do not work on the image, you should take into account that the laws do NOT describe how it should appear to an observer - in plane perpendicular to his view direction. The laws are related to the plane in which the objects are really orbiting.
--Eltwarg 14:36, 5 August 2007 (UTC)

Inclination (to plane of "sky")

Howdy, There is reference under the FACTS section of the Alpha Centauri page (for the star system): Inclination (to plane of sky): 79.24º When the word "sky" is used, does it mean Inclination to the Earth's Ecliptic, or the Inclination to the Primary Star's plane of orbit? I rather doubt that the reference relates to the Galatic Plane? To quote another part of Wikipedia, it might mean, "The ... angle between the normal to the orbital plane and the direction to the observer, since no other reference is available. Binary stars with inclination close to 90 degrees (edge-on) are often eclipsing." If that is the case, doesn't the angle change if it is based on an observer in the Northern Hemisphere, versus on the Equator, versus in the Southern Hemisphere? Thanks, Your easily confused fan, Tesseract 501@aol.com (August 20, 2005)

The definition you quote is the correct one. And, no, it does not depend on where you observe from. It may help to visualise the sky like the ancients did: as a huge spherical backdrop surrounding Earth. It is far enough that rays from observers looking at the same point from various locations on Earth will hit the spherical walls at the same angle: head-on.

Urhixidur 15:57, 1 October 2005 (UTC)

Sky appearance

A bit of a request here - would it be possible to know what the sky would look like on a planet orbiting either one of the stars? It would be fascinating to know how the sunrises and sunsets would look, how long night would be given the two suns in the sky, that sort of thing. Assuming an orbit within the habitable zone, somewhere within 0.8 to 3 AU or so depending on which star it is. Mithridates 07:46, 1 October 2005 (UTC)

Thanks! That's exactly the description I was hoping for. ^^ Mithridates 08:27, 21 October 2005 (UTC)

Assuming a planet has an orbit in the same plane as the two stars orbit each other (which is most likely), at one point in the planet's year, the two stars would rise and set together, and in fact, the star the planet orbits would appear to occult the other star. Exactly half a year later, the stars would be directly opposite to each other, and, if the planet has no axial tilt, one would be rising as the other is setting. (If there is an axial tilt, there may be periods of twilight or darkness since one star will be in the sky for less than half a day, or an overlap with both stars above the horizon.) In the intervening months, the secondary star rises and sets earlier each day relative to the primary star. This phenomenon occurs regardless of which star the planet orbits.

However, a planet that orbits both stars, at such a considerable distance that it would be colder than Pluto, would see the two stars together at all times, though varying in their positions as they revolve about each other, with the planet taking so many thousands of years to revolve that the stars' movements are much faster. GBC 19:03, 2 February 2006 (UTC)

Further to an axial tilted planet, just as here on Earth the sun remains below the horizon for anywhere from a few days (near the Arctic/Antarctic circles) to six months (at the pole), a similar effect would happen on a hypothetical planet. If it orbits A, at the Arctic Circle, the A star would rise only for a few minutes at the winter solstice, and only touch the ground at the summer solstice. B would appear only for a few minutes each day for several weeks then the time would lengthen until, 40 years later, it would only touch the horizon and not set at all for several weeks.

At the pole of such a planet, B would rise, stay up, set 40 years later, stay down, then rise another 40 years later. When it is up, you would have constant midnight "sun" while the A star is in its winter hiding below the horizon, and a second sun at all times when A is up.

These are all permutations I worked out in connection with a sci fi story that I wrote. GBC (talk) 08:30, 14 November 2008 (UTC)

Names

Here it says Rigil Centaurus=Toliman=Alpha Centauri; but http://en.wikipedia.org/wiki/Alpha_Centauri_A says Alpha Centauri *A*=Rigil Centaurus=Toliman. Also http://en.wikipedia.org/wiki/List_of_nearest_stars says Alpha Centauri *A*=Rigil Centaurus=Toliman. In my opinion, since Bayer gave the name "Alpha Centauri" to the star known as "Rigil Centaurus" or "Toliman", then Alpha Centauri=Rigil Centaurus=Toliman. Also, the "Facts" section gives apparent and absolute magnitudes, but fails to mention that these are the magnitudes of Alpha Centauri A, not the magnitudes of the entire Alpha Centauri system.

Distance

The article states in the System Components section that the distance of the binary system of Alpha Centauri A and Alpha Centauri B is 4.36 light years, while the distance to the Alpha Centauri C or Proxima Centauri is 4.22 light years. However, in the Facts section, the distance to Alpha Centauri is given as 4.396 light years. I suspect that the number given in the Facts section is incorrect or was miswritten to include an extra "9". Anchr 14:53, 13 November 2005 (UTC)

4.396 (actually 4.394 using more accurate conversions) probably comes from the Hipparcos parallax of 742.24 mas. I don't know where the value that is used in the article came from. Ardric47 22:28, 19 March 2006 (UTC)

Some of the distances may be from older sources. Alpha Centauri has been "receding" from us as astronomers refine their parallax equipment. In the 1893 World Almanac, it was reported as 3.26 light years from Earth (20 trillion miles, or 20 x 10 to the 12th power), equal to one second of parallax. By the 1960s, the distance was refined to 4.2 light years, and through the 1970s and 1980s, 4.3 light years. I learned of 4.393 (25.8 x 10 to the 12th power) light years from the website of the South African Astronomical Observatory, sometime around 2000. GBC 16:28, 8 September 2006 (UTC)

Total visual magnitude

"and contains the fourth brightest star in the sky, with a total visual magnitude of −0.01."

is the total really necessary, since, for all intents and purposes, Alpha Centauri A is effectively a point source of light as seen from Earth (well under 10 milliarcseconds) - we're not really integrating over a large surface. Richard B 03:22, 18 November 2005 (UTC)

Planets + question

Anyway we can source our claims in the potential planet section? [Here] is a primary source used at Planetary habitability which may be of some use.

Also, I'm a little confused myself about "contains" the fourth brightest star. How, for an Earth observer, is the apparent visual magnitude of A seperable from its companions?

With a telescope (or binoculars), the 2 primary stars of Alpha Cen are resolvable into distinct components, and will appear as bright as their individual app. magnitude dictate. To the naked eye, they are too close for most people to be able to split them as distinct stars, so appear as a single, brighter star Richard B 18:48, 2 February 2006 (UTC)

Hello... I just found a blog entry with some new information about the possibility of planets around Alpha Centauri. The link is [here]. I'd edit the entry myself, but I'm not quite sure how to do citations and notes, so I'll leave it to more experienced hands. -- CLB

Merger w/ Proxima Centauri

There are two reason behind the proposal.

1. They logically belong together. This article already mentions Proxima a number of times.
2. Readers looking at one article will inevitably look at the other anyway. We might as well save them the trouble.

B00P 05:53, 14 February 2006 (UTC)

I oppose the proposed merger - the two stars are each notable in their own right and merit separate articles, though they should of course refer to each other. I think it's not inevitable at all that people looking for info on one of them would be looking for info on the other as well. Worldtraveller 00:53, 17 February 2006 (UTC)

Notable, undoubtedly, but that doesn't mean that they need two articles. Sirius B is notable, but it's on the same page as Sirius A. The same is true for Alcor, which is located on the page for Mizar.

Additionally, if α Cen C deserves its own article, why do α Cen A and B not deserve one each?

In all other cases it is star systems that get the article. It makes sense to treat this case no differently from the others.

Perhaps "inevitable" was slightly overstating it; I'll stand by "likely." B00P 07:12, 17 February 2006 (UTC)

Proxima may not even be orbititing Alpha A & B, and they are separately important: Proxima is the closest star to Sol, and Alpha A & B are the closest large / stable stars. I also oppose the merge. (I also changed the title of this section: the page being merged is Proxima Centauri, and the "Alpha Centauri C" name is not universally accepted.) DenisMoskowitz 18:34, 21 February 2006 (UTC)

• oppose proxima centauri is a very notable star, that everyone would search and it would odd if that would lead to this article, it would seem a mistake in a first glance. That occured to me once. I'm not a star fan, but i wanted to know more about Proxima Centari, for my surprise it leded to this article, I'm not sure if it was in the English wiki or in another wikipedia. --Pedro 21:40, 21 February 2006 (UTC)

Oppose. Of course Proxima Centauri deserves own article.--Jyril 17:45, 1 March 2006 (UTC)

Oppose. It should have its's own article. Fosnez 13:41, 8 March 2006 (UTC)

• Oppose. They are seperate stars, so articles should be seperate. --GW_Simulations 13:23, 12 March 2006 (UTC)

• Oppose. Proxima Centauri is a unique astronomical object and therefore deserves its own unique Wikipedia entry. --SirCyan Sun Mar 12 20:57:56 PST 2006

• Oppose. I'm flabberghasted it's even come to this. Barryvalder 09:15, 21 March 2006 (UTC)

• Oppose. the age of the star system is not the same —Preceding unsigned comment added by Korbindallis (talk • contribs) 00:52, 23 March 2006

More than a month later, few are in favor. I'm removing the tags. —Preceding unsigned comment added by DenisMoskowitz (talk • contribs) 19:59, 24 March 2006

Error in the data?

The value of the inclination in degrees is the same as the orbital period in years. Could this be an error? The probability for an random coincidence of all four significant digits is about 10^-4. From Internet Stellar Data Base I get 79.92 year but no information about the inclination. Where are the values in the article taken from?--SiriusB 16:48, 7 March 2006 (UTC)

It wouldn't hurt to have references, so the values could be checked.--Jyril 20:21, 8 March 2006 (UTC)

References are very much necessary; see my comment above about the distance. Ardric47 22:29, 19 March 2006 (UTC)

---

Ah - I don't agree that Adam Strange was envisioned quite that way. The stories have him battling alien forces and saving the inhabitants of Rann -- PFS 10 June 2006 (UTC)

Pointless move

The name of Alpha Centauri system is Alpha Centauri (consisting of the stars Alpha Centauri A, Alpha Centauri B and Proxima Centauri).--JyriL ^talk 08:03, 14 July 2006 (UTC)

I agree and recommend that it be moved back. Otherwise, to be consistent, all multiple star pages should be moved. These include Capella, Acrux, Alnitak, Gamma Velorum, Dubhe, Castor, Delta Velorum, Alpha Coronae Borealis, Almach, Mizar, Gamma Leonis, Epsilon Carinae, and many more. --Fournax 12:19, 14 July 2006 (UTC)

Those pages actually discuss a star rather than a star system, whereas this article does not start off mentioning any particular star. "Alpha Centauri" is a star, the "Alpha Centauri system" is where it's located. Helicoptor 13:03, 14 July 2006 (UTC)

No, those pages discuss star systems. For example, the second sentence of the Capella article: "Although it appears as a single point to the naked eye, Capella is actually a bright close binary pair of stars along side a second, fainter binary." Alpha Centauri looks to the human eye like a bright point of light in the sky. But it's really a star system containing three stars: Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. There is no massive, compact body of plasma in outer space that is currently producing energy through nuclear fusion called "Alpha Centauri." --Fournax 13:40, 14 July 2006 (UTC)

I've added the page to Wikipedia:Requested moves. --Fournax 22:13, 16 July 2006 (UTC)

Strongly support move back to Alpha Centauri, and in any case Centauri should be capitalised. Chaos syndrome 13:13, 22 July 2006 (UTC)

This article has been renamed as the result of a move request. Vegaswikian 05:32, 26 July 2006 (UTC)

Actually, the name of Alpha Centauri is "Toliman" or "Rigil Kentauri", the term "Alpha Centauri" is a designation. But nevertheless: "Alpha Centauri" is the term most often used, so it doesn't matter much. ... said: Rursus (bork²) 20:36, 29 January 2009 (UTC)

Sky appearance from the Alpha Centauri system

There are so many unverified claims in this section. Helicoptor 13:05, 14 July 2006 (UTC)

I've added an image to clarify somewhat where our Sun would appear in the sky from Alpha Centauri. The write-up is pretty accurate, but I don't have any further references. RandyKaelber 03:24, 13 October 2006 (UTC)

When is a Cen A closer than a Cen B?

With an inclination of about 80 degrees, this means from a potential planet around one star the other star would outshine our Sun for parts of the year. Is there a method that this could be found out from the system data on the side bar?

Not sure what you mean - a planet around either would probably be in the same orbital plane as the two suns, so the other would appear kind of like a bright Saturn from the planet. Our sun would be a star in their sky, much smaller than either A or B. DenisMoskowitz 15:00, 8 September 2006 (UTC)

I was thinking about how it is the scattered light from the Sun that makes it hard to see anything else on the sky by day except Luna. It is very hard to find Venus even at its brightest (-4.6m) and most elongated from the Sun (about 45 degrees) even on a clear day unless one knows exactly where to look.

Now I was thinking that while the secondary star might appear small on the sky of a planet, if it is 6m dimmer than the primary, the scattered light would also be 6m dimmer compared to that of daylight. Also, the Sun would be a 0.5m star on the sky of a planet, therefore about 5m dimmer than Venus is from Earth at its brightest. Depending on which star would be the secondary and where in the orbit both stars are, the secondary would be between 4.6m dimmer (a Cen A from an a Cen B planet at periastron) and 8.6m dimmer (a Cen B from an a Cen A planet at apastron) so I thought the Sun might be very hard to find on the sky when the secondary is at a relatively small angle to it seen from the planet.Ambi Valent 21:15, 21 September 2006 (UTC)

I wonder what "node at 205°" is supposed to mean. Is that 205° from periastron? And would it mean after that point a Cen B is closer than a Cen A? If so, I guess it would mean the direction towards Earth, seen on the flat orbit from a Cen A, would be at 295° from periastron, or about 6 years before each periastron.Ambi Valent 13:15, 22 September 2006 (UTC)

Not sure what the heading is supposed to mean. Closer to what - a planet or Earth? Roughly every 40 years, one of the stars gets closer to us than the other. Planets in the Alpha Centauri system must orbit one of three gravity centers: Alpha Centauri A, Alpha Centauri B, or so far out that it orbits both as if they were one. From the perspective of a planet orbiting one of the two stars, the other would act with the characteristics of Uranus in our solar system - taking some 80 years to return to its original position. However, the planet would experience, in a period slightly over one tropical year, a shift of the non-primary star all around the clock - conjunction at one point, and opposition a half year after that; a quarter year after conjunction, the secondary star would be rising approximately one quarter of a day earlier than the primary star. At all times, both stars would be far, far brighter than Earth's sun. GBC 19:42, 22 September 2006 (UTC)

I meant closer to Earth. Sorry for being unclear. I think I'll make a new question which will help me answer this and other questions.

Taking the picture of the flat orbit, which star is in x, y or z direction?

On the picture, A is stationary, +x would be the direction where B is at periastron, +y where B moves toward at periastron, and +z the direction towards a viewer for whom the orbit would look flat and counterclockwise like in the picture.Ambi Valent 22:20, 22 September 2006 (UTC)

About planets

I'm not astronomer, but I have much questions about possibility of habitable planets in Alfa Centauri system. Any planet in this system must have very unstable orbit because gravitional disturbance from another star. Moreover if this planet exist it must have highly unstable conditions on its surface because different quantities of energy which planet obtain when planet is situated between stars and when planet is situated beyond one of stars. From these reasons I believe that none habitable planets are possible in Alfa Centauri system and other double-star systems. Please correct me if I'm wrong.

Actually, the energy a planet in the habitable zone receives from the other star is always minimal; when the stars are closest to each other and the planet is between the stars, it only receives about 1% of its energy from the other star. A planet for which this would be significantly different would have to be more distant from its primary star, and then its orbit would become so unstable that the other star would eventually pull it out of the orbit around its primary to a more chaotic path, probably slingshooting it out of the system entirely. And about stable orbits: Earth's orbit around the Sun is varying over the millenia between round and elliptic (from the small but persistent effects of other planets gravity, mainly Jupiter's), and Luna's orbit around the Earth even more so (from solar gravity effects), but still both have absolute limits which they don't leave, and neither would an Alpha Centauri planet. The only question is exactly how strong the effect would be.Ambi Valent 00:10, 22 October 2006 (UTC)

Is it possible to calculate the maximum distance that planets could potentially form around a star in a binary system without being disrupted by the other star? It would be interesting to note the "planet zone" as well as the "habitable zone". ⇔ ChristTrekker 16:57, 13 December 2006 (UTC)

An article in Astronomy magazine in 1982 said that for the Alpha Centauri system, the maximum distance would be 2.5 AUs from each of the two stars. Beyond that, the gravity of that star would not be dominant enough to overcome periodic tugs from the companion star. I do not know, however, the minimum distance for planets that orbited both stars as a single gravity center. 2.5 AUs is enough to include the inner solar system of our own star, so in theory, both A and B could have four planets, for a total of eight inner planets. The next question is, do those planets exist, and are two, or even one, of them at the right distance from its star for a suitable temperature to allow conditions for life, if that planet has the right chemical elements. Finally, are the planets safe or are they subject to meteor and comet bombardment due to the lack of a Jupiter in close proximity to sweep up those objects? It has been over 10 years since exo-planets began to be found, and I have not heard if anyone's been studying the Alpha Centauri system in search of planets that could be found by those methods already used to discover so many planets around stars that are so many times further away from us. GBC 17:47, 14 December 2006 (UTC)

The gravitational pull of Alpha Centauri A would be much greater than Alpha Centauri B, because Alpha Centauri A is more massive than Alpha Centauri B. So, surely the maximum distance that planets could form around Alpha Centauri A would be greater than for Alpha Centauri B? 2.0 Au perhaps for Alpha Centauri B and, maybe 3.0 Au for Alpha Centauri A. I am probably not taking into account some other factor, other than gravity, that causes the maximum distance for planet formation to be the same for both stars and I don't suppose the magazine article was trying to be that detailed.

I've looked at it again, this time how much of a temperature rise it would cause: For a planet of a Cen B, temperature at periastron would be about 2K (nearly 4F) higher than at apastron. This temperature rise starts very slowly, and only the 6 years before and the 6 years after periastron would be 1K or more warmer than at apastron. This would still mean a strong global warming and following cooling every 80 years (comparison: in ice ages temperatures are just 5K lower than between them). For a planet around a Cen A, the effects are 3 times weaker as a Cen B is three times fainter as a Cen A.Ambi Valent 15:55, 22 October 2006 (UTC)

I don't understand how it is possible. Distantion between Cen A and Cen B is only 11.2 astronomical unit, i.e. only slightly more then distantion between Sun and Saturn (9.5 astronomical unit). Both Cen A and Cen B have mass rougly equal to Sun's mass and highly ecliptical orbit (e=0.52). I don't understand how it is possible that temperature on surface of planet is varied in such small limits in these conditions. Dmitry Krotko.

I think the main mistake you're making is either forgetting that 11.2 AU is the minimum, not the average distance, or that you get just 1 percent of the energy at 10 AU that you would get at 1 AU. Let's look at the example of the planet around a Cen B again. Assuming it is earthlike, it has an average temperature of about 288 K (15°Celsius or 59°Fahrenheit). 11.2 AU is the *minimum* distance between the two stars. Since an earthlike planet has an orbital distance about about 0.7 AU (a Cen B being fainter than our Sun, with about half the energy output), the minimum distance between planet and a Cen A is about 10.5 AU. This again means it is about 10.5*10.5 = about 110 times fainter than it would be at 1 AU distance, at which it would have about 1.52 times the energy output of our Sun... so the energy that reaches the planet is 1.52/110 or about 1.4 percent of the energy of our Sun. Add the 100 percent from a Cen B you get 101.4 percent of the energy of our Sun. Temperature is proportional to the square root of the square root of energy, so you get 100.35 percent of the temperature... the 100 percent would be the 288 K, and the 0.35 percent would be 0.0035 * 288 or about 1 K... so the global average temperature then would be 16°C/61°F instead of 15°C/59°F. I'm sorry that my first guesses were way too generous.Ambi Valent 19:22, 23 October 2006 (UTC)

Thanks, that's very interesting. Amazing to think you could have a second star sitting in your backyard and yet it would have very little impact. It gives you a sense of how truly vast astronomical distances are. ⇔ ChristTrekker 16:57, 13 December 2006 (UTC)

Beta Centauri (Hadar)

Beta Centauri, according to the World Almanac, is 490 light years from Earth's sun. That is 111.36 times as much as Alpha Centauri, which is a shade under 4.4 light years. It may be that the person who deleted the info was confusing Beta Centauri with Alpha Centauri B, the latter being one of the two components of Alpha Centauri. GBC 20:49, 18 December 2006 (UTC)

The third sentence in the first paragraph is kind of confusing. I mistakenly changed it to read "Alpha Centauri A & B" until I realzed that it was referring to the the fact that Alpha Centauri and Beta Centauri, two separate stellar systems, form a visual binary. If this sentence is not essential, I suggest it be removed to avoid confusion. gar in Oakland 03:17, 7 February 2007 (UTC)

Apparent movement

40 billion years? I bet there's something wrong... I don't think either the Earth, Alpha Centauri, or Beta Centauri will still exist by then. Is 40 million years actually meant? --Army1987 22:29, 21 January 2007 (UTC)

I don't know. It was "40000000000", I changed it for "40 billion". Anyway I don't think we will still be there in either 40 billion or 40 million years. Dravick 03:32, 22 January 2007 (UTC)

Our sun is projected to last another 5 billion years. 40 million years isn't that long in astronomical terms.

And are we talking American or British "billion" here? thx1138 03:02, 30 May 2007 (UTC)

American. I think "billion" always means 1,000,000,000 these days, even in Britain. It certainly does in Australia, where we use British rather than American English. Timb66 23:50, 30 May 2007 (UTC)

The point is moot as 40000000000 was a vandalism replacing 4000 that has since been reverted. -- Paddu 18:37, 16 June 2007 (UTC)

100 dots on the trajectory image

The image with the apparent and flat trajectories of B around A seems to have 100 dots along the orbit. This may work fine to show B's higher velocity when in periastron, but the dots do not correspond to years as it appears on the image, since the space between a dot and the next would correspond to the movement in about 0.8 years. —The preceding unsigned comment was added by Ambi Valent (talk • contribs) 22:44, 18 March 2007 (UTC).

You are absolutely right - one dot is exactly 0.8 years on the published image, though there are numbers 2005, 2006, 2007 and 2008... There should have been just 79 dots - 1 dot ~ 1 year - starting on 2005 (the first dot).
It should have worked fine to
- show the changing velocity
- show the calculated position in years 2005-2083
I have not noticed this mistake - thanks for pointing it out!
I will work on fixing it.
--Eltwarg 14:34, 5 August 2007 (UTC)

Closest Pair

Wikipedia says:

• "Acrux is a trinary star located 320 light years from the solar system."
• "Beta Crucis is located approximately 353 light years from Earth's Solar System."
• "Alpha Centauri is the closest star system to our own solar system at 4.37 light-years."

The second paragraph of this article says, "Alpha and Beta Centauri are the second closest pair of first magnitude stars as seen from the Earth, and due to the effects of proper motion, they will become the closest pair around 2166, overtaking Acrux and Becrux."

Given the three statements this sentence is incomprehensible. Right now α and β Centauri are closer than Acrux and Bcrux and no motion is going to chang that in 159 years.

Could someone please explain what this sentence means? Thanks. Nwbeeson 15:12, 10 April 2007 (UTC)

Quite right. I've actually removed that statement pending clarification from whoever wrote it. What I think that person actually meant was that they were second closest in terms of angular separation. However, it very definitely came across as a blatantly incinsistent statement. 81.154.96.159 20:42, 10 April 2007 (UTC)

It has been put back in again so I have removed it. I assume it is meant to be angular separation, but the assertion is not sourced and in any case is not particularly notable. Timb66 11:51, 16 May 2007 (UTC)

This discussion was in the wrong place (top of the page whereas recent discussions must be at the bottom) which is why I couldn't find it.

Proper motion is the apparent motion of astronomical objects as seen from Earth. So it is obvious that what is meant is the angular separation of these stars as seen from Earth. May be someone can reword "closest pair ... as seen from the Earth" into something more clear.

IMHO that they will become the closest pair of first-magnitude star in another 159 years is as notable as their becoming an optical binary in another 4000 years as both give an idea of the magnitude of the proper motion, and I feel "two very close bright stars" is a feature of the night sky that even a layman can appreciate, and is hence a notable feature. Both these statements are unsourced so we should be searching for their sources (may be one of the external links...). -- Paddu 22:21, 17 May 2007 (UTC)

The text removed in [1] used to clarify that what is being talked about is angular distance. -- Paddu 13:44, 19 May 2007 (UTC)

Angular distance

Hi. The following sentence is unclear to me: "Seen from Earth, Proxima Centauri is separated by 2 degrees from Alpha Centauri A and B (about 4 times the angular diameter of the full Moon) ..." If they are so close that the human eye cannot distinguish them, how can they be as distant as 4 moons seen from earth? I can easily see lots of details on moon surface even!! -- Dwerk

A and B are a close pair, and C is a much more distant third component. Most (all?) triple systems are like this -- they are called hierarchical triples. Note that A (a G dwarf) and B (a K dwarf) are both bright enough to be seen with the naked eye, but C (an M dwarf) needs a decent telescope. Timb66 12:54, 29 April 2007 (UTC)

Sid Meier

Doe anyone else think some information on all the things Sid has named Alpha Centrauri should be included, maybe in a Trivia Section, or Other Information? I do. The space ships you build in I think all Civilization games is named Alpha Centraui I. Even a game he made, I'm quite sure, was called Alpha Centauri.—Preceding unsigned comment added by 71.192.223.240 (talk • contribs)

You are correct about the game, but in Civ you are simply sending the ship there. I don't think we need this here. See Stars and planetary systems in fiction and Alpha Centauri in fiction. Michaelbusch 22:30, 25 September 2007 (UTC)

Ah-ha. You are correct..my bad.P—Preceding unsigned comment added by 71.192.223.240 (talk • contribs)

new stars, change article

They have discovered 17 stars closer too the sun, and one hypothetical one, nemesis, most due to difficulties such as not giving of enough light, were hard to see, 3 of these confirmed stars are classified, and are the USAs worst kept secret, considering any blithering idiot with an alternative light telescope (infra-red, x-ray, microwave, or uv, for instance) can and will notice them. —Preceding unsigned comment added by Avianmosquito (talk • contribs) 02:43, 11 October 2007 (UTC)

I should add that 16 these stars appear to be part of a cluster the sun is in, and are all less then 1/2 of a lightyear from eachother. —Preceding unsigned comment added by Avianmosquito (talk • contribs) 02:49, 11 October 2007 (UTC)

Sounds suspicious to me. Can you provide a link to this "news". Astronaut 10:41, 21 October 2007 (UTC)

Alpha Centauri closest to Sol in 28,000 years?

I read in A. Ahad's science fiction series - the First Ark to Alpha Centauri [2] - that because of radial velocity and tangential velocity, Alpha Centauri system will be closest to earth in about 28,000 years from today. So this will be a favorable timescale to any earth civilization to cross over in a giant ark vehicle of a journey of 30 to 50,000 years. What is the actual calculation, informed readers here? I think the proper motion is resolvable into tangential and radial velocity components, but I dunno the methods. Pomona17 (talk) 21:56, 18 December 2007 (UTC)

I have added the closest approach and some additional general information on this.

The reference for this is an article is by Robert A.J. Matthews in the now defunct Quarterly Journal of the R.A.S. (QJRAS), 35, 1-9 (1994) entitled "The Close Approach of Stars in the Solar Neighbourhood." This has all the calculation, and information on the Alpha Centauri System. Figure 2 shows the closest star between 1 AD and 50,000 AD. Fairly simple article to read too. However the accuracy is limited mainly on the radial velocity measurements, which is less precise than the proper motions. Still the predictions are about a year or so per millennium and is good enough for the 2000 to 3000 years, but significantly larger beyond about 5000 to 6000 years either side of the present day. Hope this helps.

Adding the reference above after this entry!!!! Arianewiki1 (talk) 01:22, 27 May 2008 (UTC)

V. interesting! I like this reference. I also like the analytics of impact on our Oort cloud. However, it seems rather a shame that Mr. Matthews did not speculate on Alpha Centauri having its own system of Oort cloud (which it now seems could well have one). The story of Mr. Ahad's First Ark links the two systems using a bridge of Oort comets that seems a reasonable concept given our recent observation of other stars with vast shells of encircling material (e.g. Vega, Beta Pictoris, Tau Ceti, Fomalhaut, etc.) Pomona17 (talk) 15:00, 8 June 2008 (UTC)

Again Sky Appearance

Hello, we have tranlsated some portions of your great english article about that star into german de:Alpha Centauri, in that special case de:Alpha Centauri#Der Himmel über Alpha Centauri. Now we are looking for the main contributor of the chapter "sky appearance". The issue is: it would be nice to have some reference for that text or in other words a source of it. best regards, --FrancescoA (talk) 21:22, 24 February 2008 (UTC)

I have added additional information for you. Much of the general calculations near today are obtained using some simple formulae, mainly using mutual proper motions, radial velocities, and precession, then these are added to a certain date. Longer periods require understanding of the changes in these motions overtime. I.e. The radial velocity decrease on approach, stops, increase as it moves away. Pieces of this appears scattered in many of the professional literature - particularly of the system. None definitive. Matthews' reference in the previous post is probably useful. Note: Some can be simulated in planetarium software - though some have precision issues into the distant past or future.

Arianewiki1 (talk) 01:36, 27 May 2008 (UTC)

Hello Arianewiki1, many thanks for your answer. --FrancescoA (talk) 07:05, 27 May 2008 (UTC)

In the true orbit, closest approach was in August 1955

Is it "Earth time" of when the light reaches the Earth, or when the closest approach actually happens on α-Cen 4.2 years prior to that? Xenonice (talk) 06:42, 28 October 2008 (UTC)

Misleading appearance

Although it appears as a single point to the naked eye, Alpha Centauri is actually a system of three stars...

This is misleading. It implies that Proxima Centauri is visually a part of the brighter pair of stars. This is not the case. Proxima is actually more than two degrees away from the brighter pair. -- B.D.Mills  (T, C) 03:20, 16 May 2008 (UTC)

Proxima, although 2 degrees away has a very similar proper motion and parallax, and is very likely attached to the main binary. So this misleading appearance in the quote is actually correct, though a few doubt this based only on the lack of evidence. Ie. Proxima could just share the same proper motions, but is moving independently in its own motion through space.

Arianewiki1 (talk) 01:27, 27 May 2008 (UTC)

Good Point/ I've Fixed it!!

Arianewiki1 (talk) 20:50, 14 June 2008 (UTC)

Orbital Elements

There are some problems with this page with the quoted orbital elements. The recent changes made in the orbital elements are taken from an older source; namely, Pourbaix (2000), even though the reference by Kervella et.al. (2008) seems more modern. The values should be the ones quoted in the 6th Orbit Catalogue of the USNO, which are the later ones from Pourbaix (2002).

Suggest we should leave both versions elements on side data bar, until I can write a section about the orbital elements.

(In actuality. both are right, whose differences are within the current errors that calculated these results.)

Pourbaix (2002) data is more extensive than Pourbaix (2000), as it uses data for an older epochs to improve the accuracy!!

Discussion on this problem welcome. Arianewiki1 (talk 18:55, 15 June 2008 (UTC)

I am organising to contact the US Naval Observatory to resolve this issue Arianewiki1 (talk 20:55, 15 June 2008 (UTC)

Yes, as you point out the Kervella et al. paper adopted the orbit of Pourbaix 2000 (A&A supplement 145, 215). The orbit in Pourbaix 2002 seems preferable; this is also the orbit given in the 6th Orbit Catalogue. I have removed the older orbit. Having two orbits in the infobox confuses the reader and adds little to the article. Spacepotato (talk) 00:44, 12 July 2008 (UTC)

Actually, both are correct, but each are based on different epochs. Pourbaix 2002 is probably best, and has more accurate elements, but does not seem to match the observations at the current epoch.

Suggest we transfer the now deleted data to the discussion section until new orbital elements are produced next month. Arianewiki1 (talk 00:17, 12 July 2008 (UTC)

Sure, go ahead. If you think removed material merits discussion, you don't need to discuss before adding it to the talk page. I have not checked the relative accuracy of the two orbits, but I think it's better to pick just one orbit for the infobox. Otherwise, the reader who merely glances at the infobox might be left with the impression of an extra star. Spacepotato (talk) 17:11, 12 July 2008 (UTC)

I was going to right on these problems in a separate section, but I've delayed as I know in August a new analysis of the orbital parameters will be issued. Orbital elements are used to calculate the relative positions of the stars in past and the future. Both are correct, as they cover different epochs of the orbit. Agreed, though. Pourbaux 2002 is probably best.

I only really did this duplication to satisfy the previous author who properly referenced it. (Actually, BOTH orbits were referenced, both with different dates.)

Anyway, thanks very much for your considered comments. Arianewiki1 (talk 15:58, 12 July 2008 (UTC)

Tone & OR

While this article is generally very good, a lot of it seems to be more in the tone of a popular astronomy magazine article than an encyclopedia. Some of it seems to be based on calculations and speculations of WP editors, rather than reporting notable, reliable sources and much of the later sections verges on violating WP:FUTURE. I'm going to start by adding cite tags to the parts that seem most like WP:OR Ashmoo (talk) 12:57, 16 July 2008 (UTC)

I agree to some extent. The text needs to be tightened up and made more encyclopedic. There's also too much emphasis on what the sky looks like from α Cen.—RJH (talk) 21:15, 17 July 2008 (UTC)

I was waiting for the content to be more or less complete before chipping in with copyediting, which should address these issues. Balancing between technical and lay terms is always tricky. It looks like Arianewiki is making a concerted effort on this one (which is good as many stars haven't had this done). Cheers, Casliber (talk · contribs) 23:41, 18 July 2008 (UTC)

It would be helpful if more attention were paid to the MoS for this article. Per the MoS, I'd made revisions to bring it in line, only to see them undone.—RJH (talk) 15:08, 18 July 2008 (UTC)

Yes, I've noticed that. I have restored in the last few hours to reorganise the left duplications, but specific clarifications have had to be re introduced as there were significant factual errors. I have spent too long in the last couple of months to get the document to where it is without trying to to offend others by taking their own contributions to the document. Your changes were so broad, that I have had to fix factual statements or unnecessary duplications. Ie. The magnitudes of the stars were spread over in three different places.(much of the time was spend figuring out what you changed!

Could we instead, quickly get the logical order of the text, before refining the text (and MoS) Section by Section please. Otherwise, we will be doing this forever and a day. [User:Arianewiki1|Ariane1au]] 15:54, 18 July 2008 (UTC)

Well, no offense, but the order of the article seemed illogical, which is why I attempted to re-order it. There was also considerable redundancy. There was no way I would have supported it for FA, even if the other issues were cleaned up. Sorry for the wholesale changes, but frankly it seemed to need a big broom.—RJH (talk) 19:44, 18 July 2008 (UTC)

Appreciate the corrections in this article by both RJHall and Ashmoo. I have had to revered some of the heading (and the duplicated paragraph) to a more astronomically correct titles, but the text corrects have been very minor. Some care should be taken with exact technical terms. Ie. The difference between the apparent and true orbits is very important. Here someone removed the vital term "true orbit". Ie Explained in; and

I should comment that much of the text I've added fixed the early confusion apparent in the earlier parts of this discussion pages, where much confusion happened with earlier versions of this page. While it might be to popularist in tone, the idea was to fix the significant factual or somewhat misleading text leading others astray. As to the lack of its "more encyclopedic" nature, I think this article portrays the information better than other wiki articles. As to the perspective from Alpha Centauri view, it does placed the earlier text in good context and helps explain the earlier context of proper motion and distance. (These are not given in the wiki pages discussion these motion very well - frankly too analytical. )

The questioned section presumably without references is overall correct and provable. None is really speculation. These results can be easily calculated using the available data using simple addition, simple formula or basic trigonometry. It can be calculated in the given star catalogue references too, and shown in various astronomical planetarium computer software. Much of these same results are very scattered in the references (and those already given), and the formulae is there too, Ie., Matthews. To really formally want do this with references (like ) to your requirements would require an effort to correct more than two dozen wiki articles - and frankly don't have the time. Explaining the logic of the results would only make the text even longer.

(The image presented on the motion through the software of Celestia is an example of the overall correctness here. (I could also self-reference this, but this would not likely be considered proper under the given wiki rules.) Ie. )

Just a kind request though... If you must edit the complex flow of the whole article, please try to agree on the sequence of the logical order, then just modify each Section - section by section. Doing huge edits on complex texts are very difficult to repair or further modify in both time and effort. If Casliber is sincere in the general changes, this would help very much to improve the copyedit. [User:Arianewiki1|Ariane1au]]] 21:27, 17 July 2008 (UTC)

Would better graphics than the ones in the article improve the nature of the "speculation" so stated? [User:Arianewiki1|Ariane1au]] 21:38, 17 July 2008 (UTC)

I'll can now organise some specific references for "View from Alpha Centauri"[User:Arianewiki1|Ariane1au]] 21:58, 17 July 2008 (UTC)

One quick note. Arianewiki1, I appreciate the work you are putting in to improve the article. But if you find yourself having to do calculations for material for the article, you are probably verging on original research and/or adding info that is out of the scope of an encyclopedia article. WP:RS is a core policy of wikipedia, no exceptions are permitted. Ashmoo (talk) 12:56, 18 July 2008 (UTC)

Yes. At the very least, a reference should be provided for the formula and the values used therein (although it is okay if the values are referenced earlier). Thanks.—RJH (talk) 15:10, 18 July 2008 (UTC)

I'll have the references in due course, but I have over two hundred papers again to check the quoted information. (I think this appeared in the introduction to the Hipparcos Catalogue, which talked in much detail about the significance of the results of alpha centauri's motion and distance.)

As to your statement that this "out of the scope of an encyclopedia article. WP:RS", the same could applies to many of the same articles of the bright stars Ie. Sirius (Sirius supercluster or the 3rd paragraph on hydrogen in Sirius A's atmosphere)) and Arcturus (astroseismology)

Yes, I agree. That does need to be addressed in said articles, at least by providing a reference for the formulae.—RJH (talk) 19:42, 22 July 2008 (UTC)

I have also avoided any calculation produced by myself. I also think you must also carefully distinguish the difference between theoretical and statistical calculation. Theoretical calculations uses assumptions based on uncertain or poorly derived parameters. Statistical calculations are based on directly observed parameters, whose results values can be made with much certainty (with an error.) Alpha Centauri proper motions have been measured for more than a century, whose actual motions have been imaged photographically. (Suggest you look at several different images you can obtain in an Aladin Previewer applet in SIMBAD for Proxima or directly at , compare images to see this motion yourself.)

This also applies to the future motion of Alpha Centauri. The approach to Beta Centauri is an observed fact, and has very little doubt in the event happening in the future. As stated, many astronomical references have stated this basic fact - easily verified by data already presented (proper motions in this case) within the text.

(We also have to be careful not to have to verify needless facts. Ie 'gravity' without constantly referring to say Newton's or Einstein's original works.)

However, I do understand your point on addition of verification of sources, and have attempted to continue add references of them as time permits. "Verification" as a term, however, to some extent is all subjective - more to do with individual knowledge rather than misleading or uncertain facts. Ariane1au 13:39, 18 July 2008 (UTC)

Hi Ashmoo. The text here is both relevant and necessary. and in no way is violating WP:FUTURE "speculations about events thousands of years into the future." The reference for this can be accessed much from the from the book "Centauri Dreams : Imaging and Planning Interstellar Exploration" by Paul Gilster. This has 69 citations that I know of, and

You can read the Introduction on line at . pg.6 There is currently investigations and some results have already been applied to future missions. If we were to apply your logic here, then the accepted accredited article on Pluto regarding the Horizons spacecraft to Pluto expected to arrive in 2015 should also be removed for the same future violation WP:FUTURE. Which way should it be??

As previously stated, This information is critical to the common question about problems of interstellar distances and

removes the possible confusion in why we cannot detect planets directly. (Read earlier text on the Talk page.)

The text is neither popularist nor unrealistic. It is both relevant and reinforces the text written after it.

Please leave it there! (in the meantime, I'll attempt to reword it.) Arianewiki1 (talk) 10:56, 23 July 2008 (UTC)

The fundamental difference is that Horizons is a real spacecraft and is expected to arrive at a specific, verifiable time, barring catastrophe. Whereas the section in question is about an event that may well never happen and is chock full of assumptions and qualifiers: In the not too distant future, assuming our human technology advances enough ... Alpha Centauri may be ... would likely still take several centuries ... and this still assumes that ... If...'

From the WP:FUTURE wikipedia policy: Individual scheduled or expected future events should only be included if the event is notable and almost certain to take place & Articles that present extrapolation, speculation, and "future history" are original research and therefore inappropriate Ashmoo (talk) 11:21, 23 July 2008 (UTC)

I have significantly reduced the text size and have removed the conflicts of WP:FUTURE as suggested. It meets the requirements in my previous statements, and adequately covers your suggestion. Does this section of text now meets your expectations satisfactorily? Considering the investigation by scientists, engineers and NASA, I have no doubt such a journey will be undertaken. If it is, this will probably be heralded as one of humanity's greatest achievements - as stated in "Centauri Dreams" . Arianewiki1 (talk) 16:39, 23 July 2008 (UTC)

KINEMATICS

The changed paragraph entitled "kinematics" made by RJHall (as with Sirius) should be corrected. Proper motions nor visually binaries have actually anything to do with kinematics in astronomy. Energy in stars cannot be directly measured, only inferred. Several references, including "Double Stars" by Wulff D. Henitz (1970) state this fact. "Kinematics" is rarely used for contact or merging binaries, and the term is mainly confined to physics of mechanical or physical systems. Ariane1au 13:39, 18 July 2008 (UTC)

Since that section does not discuss radial velocity, your proposed title change seems acceptible.—RJH (talk) 19:09, 18 July 2008 (UTC)

Even if it contains a radial velocity, it is still not really the study of kinematics in double star astronomy. This is because it is easy confused with physics and energy. Also as said, energy in binaries is highly uncertain, mainly because of the uncertainty in the orbital parameters and the significant errors involved. Arianewiki1 20:50, 18 July 2008 (UTC)

Well astronomy is about physics and energy. Kinematics concerns motion without regard to the energy source or initial cause. Orbital motion and space velocity both fall under this subject heading.—RJH (talk) 22:41, 19 July 2008 (UTC)

I think you are confusing something here. In describing binary stars, the orbital motion of stars is precluded from the term "kinematics". (Read "binary star" in wikipedia, for example.) Of the dozen or so "standard texts" on double star astronomy the word is rarely used. This is to avoid confusion with "Positional and theoretical astronomy; Earth's rotation and geodynamics; Dynamics and physics of bodies of the Solar System; Solar physics; Physics of stars and the interstellar medium; Structure and dynamics of the Galaxy; Extragalactic astronomy;", which is from the introduction to; "Kinematics and Physics of Celestial Bodies" Allerton Press ISSN: 0884-5913. You can find is is a quick search in Google Books search, using the key words "kinematics binary stars" to see roughly where these astrophysical subjects - none on the motion of binary stars. If the terms is used, like the "kinematics of visual binary stars", this would be on the motion of all visual binaries through the Galaxy but not orbital motion nor proper motions.

Kinematics in astronomy description of stars is more often than not is used especially in motions of stars through the galaxy. I.e. 'kinematics" is a title say of the motion (U,V,W) of Alpha Centauri here. Kinematics also describe stellar rotation. If I were only referring to Alpha Centauri's own motion around the galaxy, then "kinematics" would be correct.

I would also suggest you consider, that (especially) "kinematics", "kinetics", "energy" and "dynamics" are often all very confusing to the casual reader, and obviously simpler terms like "orbital motion" or "galactic motion" is much preferred in this case.

As to your statement "Well astronomy is about physics and energy" is just a little naive IMO. Motion studied in physics and astrophysics are widely different, especially in methods of measurement. In physics, it is more to do with physical objects in motion. In astrophysics it is more to do with particles-like behaviour, (like stars, galactic motion, or galaxies.) Arianewiki1 (talk) 15:12, 20 July 2008 (UTC)

Sigh. I don't seem to have much difficulty find journal information on the kinematics of orbital motion. I'm also aware of the close interrelationship between physics and astronomy.—RJH (talk) 19:36, 22 July 2008 (UTC)

Again you show total lack of understanding of this issue. Sure "kinematics of orbital motion" is perhaps valid, but I noticed when you originally changed it you only used "kinematics". Surely "Orbital Motion" should suffice for the level wikipedia is aimed at - being obviously a simpler term. Yes, I've seen "kinematics" used in binary star articles, but it usually refers to the astrodynamics with "global" problems of binaries not individual ones. The reason why it is not discussed in visual binary stars is that we normally do not know the space velocities of the components in the orbit.

Examples;

1) Barkevicius, A., Gudas, A.; "Kinematics of Hipparcos Visual Binaries I. Stars With Orbital Solutions.", Baltic Astronomy, 10, 487-587 (2001). The article (pg. 481) is about about "Computed galactic velocity components and other kinematic parameters are used to divide the same stars into kinematic groups." (Hence, it is NOT about the orbits of binary, it is about using the galactic motions." Furthermore, they say;

"The number of publications concerning kinematics of visual binaries is very limited, especially for stars with known orbits. We can only mention Eggen's (1959) not analysing the distribution of several dozen stars in the plane of the galactic space velocities components of U,V and W,V. Eggen (1965) also calculated the space velocity components of 228 binary stars with known orbits and investigated the dependence of distribution of stars in the U, V plane..."

Perhaps you should read also A,E, Roy standard text "Orbital Motion". He says;"The whole field of orbital motion studies (celestial mechanics, astrodynamics, stellar kinematics, stellar dynamics, binary motion, and so on..." If kinematics is with binary stars, why is it written as separate studies?

What more proof do you need? - and this is the definitive paper!!! As I said before, normally the term is not encouraged to be used for binary stars - something you stubbornly refuse to accept. Arianewiki1 (talk) 08:23, 23 July 2008 (UTC)

Changes in Pages

Thank to both you for wasting the last eight hours for me to fix this mess! It seems pretty mean to me attempt to undermine the whole text by wanting everything to nth degree verified by reference. i have read the Style manual you have referred and have slowly being trying to fix it. Unless you have additional facts or references of your own, please leave the structure alone until I can atleast fix the references them. Please! Ariane1au 14:46, 18 July 2008 (UTC)

Unfortunately there is no equity in sweat. The amount of time you spend editing this article doesn't give you ownership of it. I'm also unclear what your feelings have to do with the verifyability of this page. Either it is properly sourced or it is not. At present it is most definitely not. The tags are there to point out critical issues; not to hurt your feelings. I think you may be taking this entirely too personally.—RJH (talk) 19:07, 18 July 2008 (UTC)

I have begun to include references to these pages, which now total nearly 80. i am not taking it personally, because I do really know what I'm talking about. To get to the required reference to the degree you have stated will total an estimated about 160-170. i can also reference every sentences, but is that is how far you want me to go? Ariane1au 20:46, 18 July 2008 (UTC)

The subject is covered on Wikipedia:Citing sources. In particular, see: "When to cite sources". Your estimate for the required number of references is probably high, but I wouldn't consider 100 references for a well-cited article to be excessive. (For example, Atom has 131, Galaxy has 103 and Supernova has 108, all of which are now FA. But you may be able to get by with a lot less if you can find comprehensive sources.)—RJH (talk) 22:26, 19 July 2008 (UTC)

Your quoted examples here seem to refer to specific definitions of general objects. One would assume that knowledge of binary stars would have more references that some specific object. I think 100 (or 160) references exceeds anything for individual astronomical objects that I've read here.

As to the point about finding more "comprehensive sources" is more difficult than you think. There are about a dozen good sources, but little on specifically Alpha Centauri. Specific points are actually scattered throughout the literature, and while sourcing the information is in the hundreds of references might be available, the most important or recent (or less contradictory).

As to some of the issues here, I suggest you read scientific realism, and especially understand "the vagueness of the observational-theoretical distinction." (I.e. referred to by Casliber) For example, how do you refer to a logical conclusions, based on definable behaviour. I.e. A two planetarium programs that can demonstrate same fact is true.

These especially applies to the much of the text in "View of this system")

Note: To save me some time, could you point out which sections here need citations. As I see it;

- Paragraph 1 does not need any references, as the data is simply logical and is not very contentious

- Paragraph 2 is the same.

- Paragraphs 3 and 4 is easily proven from the previously distances.

Yet based on the complaints here, I will added the calculations in the references. (Like in Proxima Centauri) Would that be acceptable?Arianewiki1 (talk) 16:02, 20 July 2008 (UTC)

Okay, let's start with dropping the assumptions. I'm quite aware of how difficult it can be to find suitable references. But if we are unable to find suitable citations, how can we be sure the information presented is reliable? I don't believe we can. If no citations are to be had, one approach is to move the text to the talk page and give the reason. Otherwise, it is not clear that the unverifyable text should even be in the article.

As for text needing verification, let me just give an example: the "Observation" section, paragraph 2. There are no citations that demonstrate that:

• Alpha Centauri is one of the stars of The Pointers with Beta Centauri or Agena / Hadar.
• Both stars, including the Cross, are too far south to be visible for most northern hemisphere observers.
• South of about -33° latitude, α Centauri becomes circumpolar...

See Sirius#Visibility and Vega#Visibility for examples of proper citation in Featured Articles. Clearly I'm not saying it has your task to address this issue. But it does need to be addressed at some point if we want this article to meet the highest standards of wikipedia.—RJH (talk) 19:29, 22 July 2008 (UTC)

This last examples here just simply preposterous. Circumpolar stars do not needed to be cited as it is verifiable by the definition of "circumpolar" by simple geometry I.e. Actually 90 deg minus the declination; and is common sense. This esoteric fact cannot be disputed - its really a basic definition. (NOTE Even the wikipedia article, I notice, on Circumpolar stars is also factually wrong - but that will soon be fixed!)

"The Pointers" are known as such by amateur astronomers and the majority general population in the southern hemisphere - and is verifiable without much thought. (You can see it plainly in the attached figure of the constellation and supported by explanation after it. Furthermore, the logical that the Southern Cross generally cannot be seen from much of the southern hemisphere - else why is it called "southern." I note, just because it can't be seen in much of North America - and is not fact there - does not mean it is not common knowledge elsewhere. "Alpha Centauri just is clearly synonymous as "The Pointers"! Plain and simple. Just because someone cannot see an object in the sky does not mean something does not exist. I can verify it by going outside and seeing it with my own eyes! What more proof do you need? (As a general example, do I have to verify I'm using a computer to write this when it is sitting in front of me? Of course not.)

It is just silly to say "...how can we be sure the information presented is reliable?" Again clearly note; "...not every notable view on scientific topics is documented in science journals."

Surely all these example is made as a joke?

Also note, you overall statements are strongly discouraging others to contribute to Wikipedia itself. While references and citations are important, there is no need to define text to the dictionary level. If we need to define text to such a degree, it becomes all reference and makes understanding the text far more difficult.

As for making this among the "Featured Articles", I don't think I recall me stating I was aiming to do so.Arianewiki1 (talk) 09:07, 23 July 2008 (UTC)

Arianewiki, you are doing great work on this article and your enthusiasm is appreciated. However, RJH's comments are not at all 'preposterous'. He is simply pointing out basic, foundational wikipedia policies. Since you say you are new to WP, I would ask you to read (or re-read) WP:Verifiability. Regards, Ashmoo (talk) 09:43, 23 July 2008 (UTC)

Arianewiki - whilst I agree that whether something is circumpolar or not is just geometry - and that you can just go outside and see that something is a pointer star - one of the benefits of citing sources is that someone without any technical knowledge or ability to just go outside and see Alpha Centauri (e.g. I live too far north - and it never even rises above my horizon) is able to verify that a statement is true. Richard B (talk) 11:43, 23 July 2008 (UTC)

RichardB. and Asmoo. As an example, using RJHall's earlier reference of "proper" citations are applied to Sirius#Visibility (his example), he gives "proper motion" in the section of "Kinematics" but not with a citation.

(Also noting again that "Kinematics" is the incorrect terminology regarding the text. The solution to this seem to be moderation, as RJHall will not even concede the essential error in terminology. I.e. How else do you solve this? Sirius' motion is defined as a "High Proper Motion Star", which defines the basis of the apparent motion. "Kinematics" in this instance in ambiguous, because the explanation could be the motion of the Sun (or Earth) in space OR Sirius. Here the term "High Proper Motion Star" says specifically it is Sirius as viewed from the Earth.)

Another good example in the same Sirius article is of a similar statement to the issue here "Sirius can be seen from almost every inhabited region of the Earth's surface, with only those living north of 73 degrees unable to see it.", which is also not citing any source. Simply to reaches the same conclusion as the "circumpolar" statement being questioned here. Is this not the same as "... is that someone without any technical knowledge or ability to just go outside and see Alpha Centauri." ?

So. Do we cite my line, or do we now insist we cite Sirius as well? It is one or the other isn't it? Arianewiki1 (talk) 12:17, 23 July 2008 (UTC)

I've just fixed the question regarding the circumpolar nature of Alpha Centauri and associated text. I have add the reference / citation for the text and calculation to find it. Furthermore, I have also corrected the grossly wrong article Circumpolar stars Wikipedia, and have added the actual explanation and references for that too. (At least this now solves the earlier points of contention!) Arianewiki1 (talk) 14:24, 23 July 2008 (UTC)

Magnitudes

The magnitudes here for alpha centauri should be in the introductory paragraph as it is for all other single stars listed in Wikipedia. Ie. Sirius, Canopus, Capella, Achernar, Vega, etc. Either fix all these other stars, or leave this one! (Magnitude are verified by the List of bright stars

"When considered among the individual brightest stars in the sky (excluding the Sun), Alpha Centauri A is ranked fourth at -0.01 magnitude, being only fractionally fainter than Arcturus at -0.04v magnitude. Alpha Centauri B at 1.33v, and is ranked twenty-first. By total visual magnitude Alpha Centauri AB shines at −0.27v, which is brighter than Sirius, Canopus and the fourth brightest star in the night sky, Arcturus."

Should be;

"By total visual magnitude Alpha Centauri AB shines at −0.27v, which is brighter than Sirius, Canopus and the fourth brightest star in the night sky, Arcturus. When considered among the individual brightest stars in the sky (excluding the Sun), Alpha Centauri A is ranked fourth at -0.01 magnitude, being only fractionally fainter than Arcturus at -0.04v magnitude. Alpha Centauri B at 1.33v, and is ranked twenty-first.

This is now in the introduction, where it should be. Please leave it there. Ariane1au 14:48, 18 July 2008 (UTC)

The point is not that the information is in the lead: it is that the information is not in the body. The lead is meant to be a summary. It should not contain unique information that is not also covered in the main article. I.e. put it in both places. Please, please, PLEASE study the Wikipedia:Manual of Style, otherwise I will need to keep remediating your well-intentioned, but non-standard revisions. It is necessary to follow the MoS if this page is ever to reach Featured Article standard.—RJH (talk) 19:02, 18 July 2008 (UTC)

See comment on the "Observation note" below. Arianewiki1 (talk) 19:00, 20 July 2008 (UTC)

Sorry this can't be right. If this is as you say, then looking at the Bright Stars listed in wikipedia now should have their magnitudes duplicated. Ie. Sirius, Canopus, Achernar, Acrux, Polaris, etc. You are applying seemingly random rules which don't match other documents of the bright stars! Furthermore, I've are removed it from the main article, and moved it up to the introduction. (I'll check and remove it now, if that is, it is still there. It is only there once! So as far as i can see, either this article is wrong, or the majority of the other stars detailed in wikipedia are wrong. Really it comes down to either the 'manual of style' or many similar 'pages' that are consistent in structure. Arianewiki1 20:45, 18 July 2008 (UTC)

Only a few of the star articles have been able to be promoted to FA, and those all meet the MoS. I'm completely unimpressedby the argument that many star articles don't satisfy the MoS, and so we should just ignore the guidelines. That just means those articles don't measure up to the required quality. Believe me, I'm doing my best to address that, but I'm only one person.

The MoS was put together to minimize these sort of disputes, and the guidelines are generally well thought out. Otherwise we'd be endlessly debating about how to format articles. But if you're going to ignore the MoS then the article will not get past the FA criteria and probably won't even be considered a GA. At that point you'll have to bring it in line with the MoS anyway, or get out and let somebody else do it.—RJH (talk) 22:35, 19 July 2008 (UTC)

The magnitude data is not in the main text, but is only in the introduction, like the other bright stars. I also noted in the previous edit of yours, you removed it from the introduction altogether, and just placed it below. I.e. no duplication. Clearly your suggestion is already "non-standard'. Arianewiki1 21:01, 18 July 2008 (UTC)

Sorry but your logic is flawed. The lead need only be a subset of the body. Information in the lead can be expanded upon in the body, but information in the body need not be in the lead. Ergo, moving information from the lead to the body is not "non-standard". Doing the reverse conflicts with the Manual of Style, and usually requires more solid reasoning.—RJH (talk) 22:03, 19 July 2008 (UTC)

I've made a compromise here, which should satisfy your point and is consistent with other star pages. However, the introduction is now too short - especially compared to the introduction in the Proxima Centauri wikipedia page.Arianewiki1 (talk) 19:04, 20 July 2008 (UTC)

A heuristic I've seen for the lead section is to have roughly one paragraph per major section (maximum of 4 paragraphs per the guidelines). Personally, when I put in a lot of work on an article, I usually leave completion of the lead summary until near the end. (I took that approach with the Proxima article.) The lead often seems to be a point of contention for a completed article; I've seen long debates just over the wording of sentence fragments in the lead. Hence it's usually a good idea to get that part right.—RJH (talk) 19:10, 22 July 2008 (UTC)

Surely, that's your own opinion. Not everyone would agree. Also isn't a good article one that gives information useful to a majority of readers? I.e. The stars being resolved in a 5cm. telescope means the double star can be view by the reader - necessary or not. However, point taken.Arianewiki1 (talk) 09:26, 23 July 2008 (UTC)

Observation

The text here does not need verification, as everything here is already stated on other pages throughout Wikipedia. Ir Proxima Centauri, Southern Cross, Centaurus, List of brightest stars. I have removed the unnecessary unverified text block. All are properly referenced through [[ ]] Arianewiki1 14:51, 18 July 2008 (UTC)

Wikipedia pages are not considered acceptible sources for verification, at least when you try to take it throuth the FAC. The problem is that (a) not all of those linked pages are properly referenced and (b) those linked pages are subject to revisionism and vandalism. So, in short, the references must be on this page.—RJH (talk) 19:04, 18 July 2008 (UTC)

Yes, but this means now that more than 30 pages I've referenced in the article also now need references as well to make them correct. Therefore by you own logic, the references between Wikipedia sourced have to be transposed between both pages.

Regardless, as previously said, they will all be referenced. However, let me do this, and then if you must, make the necessary edits. Arianewiki1 20:08, 18 July 2008 (UTC)

Sorry but at this point I don't think I can sympathize. Myself and others have done the same sort of task many times on longer and more challenging pages. If you would like more enlightenment on the process, take a look at the commentary on WP:FAC.—RJH (talk) 22:22, 19 July 2008 (UTC)

Your tone here is concerning. There has been few challenges for this page for some time, except from two specific writers (you and Amoroo). While your guidance is very much appreciated, and you have given me the time to begin referencing process, clearly this page is far from feature article status nor good enough for nomination, at least until the referencing and some more editing is done. The hardest thing with this page is that it will be accessed by many novices, especially school children, just because it is the closest star to us. Sure it has to be accurate, but it must also be readable. Presently, the most common questions are; Where is it?, How close is it?, How bright is it?, Does it have planets?, Can planets support life? At present the general structure and depth of knowledge satisfies this point, and follows logically and increases in complexity down the page.

I should point out though, there are also many missing details that need to be considered or added. I.e.

- The origins of the important orbital data (with the issue of an orbit update for the USNO data next month),

- The current detailed investigations by NASA to send a interstellar spacecraft there, (might need a separate page)

- The high importance (historically and currently) of this binary system in understand the Sun and other solar-like stars, etc.

Arianewiki1 (talk) 18:58, 20 July 2008 (UTC)

Yes, I'm particularly concerned about the brevity of details concerning the stars themselves. There really isn't much information here. I've tried to add some details over time, but it obviously needs more work.—RJH (talk) 19:12, 22 July 2008 (UTC)

Being factual is one thing. Being current, is another. As to say "There really isn't much information here." is a bit condescending. Based on the available information in the literature, not much else can be said - at least towards the general level of the reader. I.e. What is the point of talking about the strength, of say, the surface gravity of the star. The steps to understand a simple statement is far more than someone needs to investigate. It is not necessary. Read the absolutely sterile text "Encyclopaedia Britannica" on Alpha Centauri is clearly nowhere near as precise! Arianewiki1 (talk) 09:41, 23 July 2008 (UTC)

K Spectrum stars like Alpha Centauri B may be very well suited for life. [3] What will happen when Alpha Centauri A becomes a red giant? Are the two stars close enough for that to cause problems? Will Alpha Centauri A become a Supernova? Proxima Centauri (talk) 08:11, 11 August 2009 (UTC)

Minimum telescope

The article states that:

However, the pair can be split by telescopes as small as 5 cm in aperture.

The Dawes limit for a 5cm aperture is 11.6″/5 cm = 2.3 arcseconds. The semimajor axis for this system is listed as 17.75″—much wider than the minimum, so something is amiss. It looks like a set of field glasses would suffice: 7mm minimum.

Covington, Michael A. (2002). Celestial Objects for Modern Telescopes. Cambridge University Press. pp. p.127. ISBN 0521524199. {{cite book}}: |pages= has extra text (help)

—RJH (talk) 19:45, 18 July 2008 (UTC)

Yes. The minimum separation is c. 2 arcsec, but the brightness of the stars make it difficult to to use the Dawes limit, which is assumed to be 6th magnitude stars. At maximum the stars are resolved even in binoculars, but more difficult in 15cm if close. The average of 5 cm is probably best, and is quoted in several amateur sources. Arianewiki1 20:20, 18 July 2008 (UTC)

Amateur sources may be considered unreliable and could be challenged during FAC, so more professional sources are preferred (including books). The current separation is 13″,[4] which is much wider. I think you are stretching things when you say Dawes limit is invalid; it usually only becomes problematic when the stars differ greatly in magnitude. Having two stars of similar magnitude like this shouldn't hinder matters. I think the article text needs further clarification on this matter.—RJH (talk) 22:17, 19 July 2008 (UTC)

Again clearly you just show your understanding of this is limited. Alpha Centauri is a unique example, because the brightness of the components. It is interesting to see that Dawes limit quoted in wikipedia is also quite wrong.

Dawes' limit is defined as "resolution of two stars of 6th magnitude at 550nm." (5550 Angstroms for US units) {"Binary Stars" by Robert Aitken pg. 56-58 (primary reference)] He (and Lewis) did the original experiments on this, based on actual observations and theory, and AItken says on pg.57-58. "...in general this formula [Dawes' limit] gave values which were too small even for the bright equal stars." Based on this, Robert Aitken once made some general useful equations determining telescopic resolution based on his own experiences. His created this list to guide observers into deciding the minimum separations of pairs for making micrometers measures before the systematic errors became too large for useful results.

In average observing conditions, he determined that discernible clean division of the Airy Disk find the limit of separation was Sep. = 13.84" / A (cm) or 5.45" / A (inches). This is only about 18% higher than the Dawes limit. However, these values change significantly depending on the stellar magnitudes, the Δm and the magnification being used. Consequently, observers like Lewis (“The Observatory”; 37, 378 (1914)) found by testing several different telescopes, that the Dawes formula gave too smaller values even for bright equal magnitude pairs. Furthermore the average observer should see these much more realistic limits.

In the case of Alpha Centauri, the Dawes' equation cannot by applied very well. But the real point, that "However, the pair can be split by telescopes as small as 5 cm in aperture. is true for a majority of the orbit, and is true for the present separation, and is true for the question by you. (Covington, by the way, is a secondary source.)

Interesting, your figures in the question are wrong. 5cm is the minimum aperture of most telescopes. The field glasses of 7mm do not exist, as this is usually the amont of magnification in 7×50 binoculars. (50 is the aperture size in millimetres. Ie. 5 cm.)

As to the separation, read the Alpha Centauri referenced text. The 'actual' values are; "The observed distance between the stars is now 8.29 arcsec through P.A. 237 degrees (2008) reducing in the next year to 7.53 arcsec through P.A. 241 degrees (2009).", which come from the actual HIGHEST source, the "6th Catalogue of Binary Stars" of the USNO using the orbital elements already referenced in the sidebox. The Sky and Telescope reference here is in fact actually a tertiary source! (So much here for your example of "Amateur sources may be considered unreliable and could be challenged during FAC" !)

If you really need to reference this statement, and it would require probably half-a-dozen references to verify it. If you wanted such detail, the references or the whole text would now be over 1000! The statement here is a reasonable assumption based on just logic and common sense. It really does not need clarification. (If you want to read about this in more detail, see Observing the Apparent Orbit , and reference this instead of me.

Note: On this same page, is "The Apparent Orbit", showing the past measures and the separations, which I believe was obtained in a personal communication with Dr. Mason of the USNO. (According to you statements, how does someone reference this if the data is not published anywhere nor is not an "amateur source." Common sense tells you it is clearly verifiable, and is "...not every notable view on scientific topics is documented in science journals." which you seem hell-bent to quote me via the Wikipedia rule book!!)

PLEASE NOTE.This particular example here is also bordering on "Gaming the system" WP:RS, and is especially problematic because "...not every notable view on scientific topics is documented in science journals." I've considered WP:M by a might be best through mediation of a third party, but clearly this could be resolved through common sense than conflict. Unfortunately, if this 'attitude' continues, there maybe no other choice.

Please also note: I'm new to this wikipedia I process, and I have been learning on the way. Obviously, I'm not as experienced as you (RJHall), but I am writing text on something I have intimate knowledge and experience, have written about, and and as a southern observer (I believe you live in the northern hemisphere and can't actually see this star), have observed and measured this star for almost 30 years. (None of my own references are in the text] The article on Alpha Centauri has improved immensely since I've began working on it, and the original had only a few primary references. Much of the earlier confusion and discussion on this "Talk Page" has also been eliminated, and I am more than willing to solve problems. `Arianewiki1 (talk) 17:47, 20 July 2008 (UTC)

Seems like you're getting into a bit of a rant here and making assumptions about me that are unfounded. Fine. At any rate, the modified sentence in the text seems acceptible. Thanks.—RJH (talk) 19:17, 22 July 2008 (UTC)

The assumption made about you are solely based on the information given in the Wikipedia biography - you wrote it. My point is you seem more than happy to quote all the WP rules at me, bur you clearly seem to have difficulty applying this to yourself. Solving issues can be done WP:M. when things can't be resolved. If you want to go down the path - well that's up to you.

As for the reply on the resolution of the stars I notice you just haven't commented. Without deliberate malice, your original assumptions were clearly incorrect (verifiable). Accusing me of a "rant" as a deflection shows no evidence of even slight acknowledgement of contrition for the sake of harmony. Pity. Arianewiki1 (talk) 10:16, 23 July 2008 (UTC)

A word of advice Arianewiki1. Before threatening Mediation, I would advise you familarise yourself with WP:V & WP:OR. As I am fairly sure you would lose a mediated dispute against RJHall on this matter. I don't mean this as any sort of snark or threat, but just as friendly advice to someone who has just started wikiediting. Ashmoo (talk) 10:37, 23 July 2008 (UTC)

True, but I threatened no-one. I just stated fact. The original question stated that; "something is amiss", which has been shown in my detailed reply as false. It is neither violating WP:V & WP:OR, and is in fact actually meets "Reliability in specific contexts." If RJHall can fix the problem of references for this statement, he could easily add it with much difficulty. It seems I'm doing all the significant advancement of the article, while unnecessary scrutiny is being applied to quite irrelevant issues of validation when what is clearly stated is plain common sense. (Sadly, after these I now now beginning to see why so many people often regard Wikipedia as a waste of time, and don't want to contributing to the process. I'll likely see the end of this process for this article, but I will probably won't be bothering for anything new or existing.) Arianewiki1 (talk) 11:47, 23 July 2008 (UTC)

Arianewiki, it can take a while to get used to the wiki-paradigm WRT sourcing etc. but I have found it worthwhile :) I am no expert on stars so can't offer any opinions but am happy to copyedit. Cheers, Casliber (talk · contribs) 01:32, 7 August 2008 (UTC)

Mass of Proxima

RHall, the mass ypu quote is actually a secondary source, is not based on primary data. The mass based on current acknowledged references is 0.11 MΘ NOT 0.12 or 0.123Mʘ as ypu seemed to have referenced. The values you quote are from Baraffe et.al (1998), and not the reference stated in the wiki article. (Read the actual text) They are secondary, as they are obtained by the MLR (Mass-Luminosity Relationship) measurements and the theoretical mass-luminosity relation, with an assumed 5% error. I.e. Read Baraffe, I., Chabrier, G., Allard, F., & Hauschildt, P. H. 1998, A&A, 337, 403. Considering the gross errors, it would be best to say the mass was 0.11Mʘ or 0.12MΟ. The MLR accuracy, if you want to use this quote, the value should be 0.12M at best. Based on the primary source of mass via the orbital and distance values, 0.11±0.05Mʘ is much better. Frankly, if I was being difficult, 0.11±0.05MΟ is the about the current result, but the difference between 0.11 and 0.12 is insignificant to what we presently know about this star.

Note : Please be aware that not every value quotes by some source is definitive. The result is derived from the parameters that are defined by the paper presented. Whist a paper in 2008 might seem good, it does not mean that the measure is right. It only means the criteria of the assessment was standardised across the examination of the paper.Arianewiki1 (talk) 21:01, 6 August 2008 (UTC)

Please see Talk:Proxima Centauri#Mass of Proxima. Spacepotato (talk) 21:28, 6 August 2008 (UTC)

Issue with opening

The opening says that Alpha Centauri is a "star." That doesn't seem right to me. Strictly speaking, surely the term "Alpha Centauri" should refer to the star system as a whole. The individual stars are Alpha Centauri A, etc. I'll wait to see if anyone else has any comments before making changes myself though. Kevin Nelson (talk) 12:47, 8 August 2008 (UTC)

Alpha Centauri is a "star" to the naked-eye, seen as any other. As the Alpha Centauri is also a binary star, the text needs to be expanded to discussing the "star system". The article follows this logical, in increasing complexity down the page. Ie. First It is a single star is the sky (and closest star) , a binary star, a multiple star (including Proxima).

Frankly, as the one who reorganised the text into the current structure I find it hard to satisfy all those on this exact issue who seem to want to mix up the text again and again. Ie. RJHall on 16th July, who took out the text in the heading, and placed it in the different sections be below it. I.e. The text read;

---------------

Version 16th July 2008

--------------

Alpha Centauri / α Centauri / α Cen, also known as Rigil Kentaurus, Rigel Kent, or Toliman, is the brightest star in the southern constellation of Centaurus and an established binary star system, Alpha Centauri AB (α Cen AB). It appears to the naked-eye as the third brightest star in the entire night sky, being only outshone by Sirius and Canopus. By total visual magnitude Alpha Centauri AB is −0.27, which is just fractionally brighter than the fourth brightest individual star in the night sky, Arcturus.

In the southern hemisphere Alpha Centauri is known as one of The Pointers, along with Beta Centauri or Agena / Hadar, as both stars directly point towards the constellation Crux - the famous Southern Cross. The Pointers were so named because they easily distinguish the true Southern Cross from the less bright asterism known as the False Cross. The star Beta Centauri lies some 4.4 degrees further west from Alpha Centauri, mid-way between the Southern Cross and α Centauri.

Both stars are presently too far south to be visible for most northern hemisphere observers. Those below the northern latitude of +33 degrees who can see α Centauri, will find it lying close to their southern horizon during the northern summer. South from about -33 degrees latitude, α Centauri is circumpolar and never sets below the horizon.

Alpha Centauri has the primary distinction of being the closest of all the stars visible to the naked-eye in the night sky. Its true distance is about 1.3 parsecs, or 4.37 light years.

---------------

OR the 30th May 2008 Version

---------------

Alpha Centauri / α Centauri / α Cen, also known as Rigil Kentaurus or just Rigel Kent, is the brightest star system in the southern constellation of Centaurus. It appears to the naked eye as the third brightest star in the entire night sky, being only outshone by Sirius and Canopus. By total visual magnitude Alpha Centauri AB (α Cen AB) is −0.27, which shines just fractionally brighter than the fourth brightest individual star in the night sky, Arcturus. In the Southern Hemisphere Rigel Kent is known as the outermost "pointer" to the Southern Cross, but it is too far south to be easily visible for most northern hemisphere observers. The other inner "pointer" is Beta Centauri or Agena / Hadar. This star lies some 4.4^o further west of Alpha Centauri, in between the Southern Cross and α Centauri itself.

---

OR the 24th April 2007 Version

---

Alpha Centauri (α Cen / α Centauri, also known to astronomers as Rigil Kentaurus), is the brightest star system in the southern constellation of Centaurus. Although it appears as a single point to the naked eye, Alpha Centauri is actually a system of three stars, one of which is the fourth brightest star in the night sky. Alpha Centauri is famous in the Southern Hemisphere as the outermost "pointer" to the Southern Cross, but it is too far south to be visible in most of the northern hemisphere. The two brightest components of the system are too close to be resolved as separate stars by the naked eye and so are perceived as a single source of light with a total visual magnitude of about −0.27 (brighter than the third brightest star in the night sky, Arcturus).

Alpha Centauri is the closest star system to our own solar system at 4.37 light-years distant (about 41.5 trillion km, 25.8 trillion miles or 277,600 AU). Proxima Centauri, often regarded as part of the system, is 4.22 light-years distant[1]. Alpha and Beta Centauri are the second closest pair of first magnitude stars as seen from the Earth, and due to the effects of proper motion, they will become the closest pair around 2166, overtaking Acrux and Becrux.

Alpha Centauri's relative proximity makes it a logical choice as "first port of call" in speculative fiction about interstellar travel, which assumes eventual human exploration, and even the discovery and colonization of imagined planetary systems. These themes are common to countless video games and works of science fiction.

===================

As to changing this (again) , please leave it as is until we at least have a stable version and general comment via the process. I think the introduction and follow up section adequately explains this star on different levels as a "star", "stars" and "gravitational system".

Comment:

Other comments of similar vein to this are

♦ degrees verses " ° "

♦ SI units versus not SI Units (especially important in the non SI standard mix in the global "starbox")

♦ Standard astronomical practice for using metric over US or UK imperial units

♦ Significant places with numbers and rounding

♦ Numbers without any quoted errors, etc.

This wikipedia method of text structure and "buffeting" by so many so-called 'experts' is so frustrating - mainly as the variances between what someone thinks needs to be said or not, what is important or not important. Even the citations reviews are totally haphazard, as one can quote (or not quote) from any source they want without understanding the issues behind the actual information. I.e. Sometimes it's really like monkeys trying to write Shakespeare!

Arianewiki1 (talk) 18:53, 9 August 2008 (UTC)

Alpha Centauri versus α Centauri

We have to decide whether to use the Greek letter α or to spell it out as Alpha. Either is correct, but we need consistency. My vote is to spell it out as Alpha. Kevin Nelson (talk) 08:33, 9 August 2008 (UTC)

Alpha is stated in the beginning of the article, but as we descend through the text I have used the abbreviation of α Cen or α Centauri. The text is very confusing with Alpha Centauri (general), Alpha Centauri A, Alpha Centauri B, Alpha Centauri C, and Alpha Centauri AB, as each has a specific meaning as an astronomical object. I think Alpha Centauri is logical for general text, but for the specifics α Cen A, α Cen B, α Cen C and α Cen AB is better and scans more easily. Also the article would not be as long. Were the name short like like Sirius, we would use Sirius A and Sirius B, but Rigil Centaurus A etc. is too cumbersome. This usage is similar to what appears in the literature, and according to Wulff Heinze and Robert Aitken is preferable.( See list references in article)

Note: I reverted the whole text once before on this question. Arianewiki1 (talk) 17:43, 9 August 2008 (UTC)

Like Kevin says, either is acceptable, but we need consistency. As it stands, there are multiple instances where the name used changes within a single paragraph.

Looking through the article, it seems like the standard (if there is one) is to spell the name out in full at the beginning of a paragraph and then use one of the abbreviated forms for subsequent uses. Is this your impression? And if so we should decide which abbreviation to use. Ashmoo (talk) 12:38, 13 August 2008 (UTC)

Also, the intro says that Alpha Centauri is a binary star system, but the 'Nature of the System' section calls it a triple star system. Then the next line implies that Alpha Centauri AB refers to the triple system. These issues need to be resolved, as the text is very unclear to someone who doesn't know all about Alpha Centauri in the first place. Ashmoo (talk) 12:53, 13 August 2008 (UTC)

Kevin and Ashmoo.

I have added the section on the component designations and have fixed the problems with the ambiguity. This explains why the terminology is as it is. I have added further explanation on the Wikipedia under Double stars, which also explains the difference between visual double star types universally accepted as the definitive reference the Washington Double Star Catalogue or WDS.

Is this satisfactory now???

Arianewiki1 (talk) 17:42, 17 August 2008 (UTC)

That looks good. Cheers, Ashmoo (talk) 12:56, 20 August 2008 (UTC)

Rotational period of Alpha Centauri B

The article claims that Alpha Centauri B has a rotational period of 41 days and gives a citation to Bazot, Bouchy et al (2007). However, that paper is devoted to Alpha Centauri A and says nothing whatsoever about Alpha Centauri B. If no one can come up with another source, then mention of Alpha Centauri B's rotational period should probably be deleted. Kevin Nelson (talk) 09:21, 9 August 2008 (UTC)

I haven't been able to find this orbital period as quoted, but it does appear elsewhere. I'd happily add it when I next read some new references. I have been the one doing much of the additions, editing and referencing of the article, which has been made more difficult as I started the improvement with an established text which was not properly referenced at all. (I know of another four or five problems like this in the whole text.)

NOTE: At the instant, I am hopefully getting to a stable version so I can find the additional the missing citations for a formal review. However, The insistences the relentless citations for minor trivialities by RJHall has especially has made this far more difficult. Matching this article with the terribly complex and difficult to read (especially for novices and even those with my specialised experience) in the separate article on Proxima Centauri is not making the task any easier.Arianewiki1 (talk) 17:59, 9 August 2008 (UTC)

Established binary?

"Alpha Centauri (α Centauri / α Cen), also known as Rigil Kentaurus, Rigil Kent, or Toliman, is the brightest star in the southern constellation of Centaurus and an established binary star system..."

Aren't all true binary star systems by definition established binaries? A double star where the constitutent stars are not physically gravitationally bound together in space, but merely happen to lie along our line of sight, is often referred to as an 'optical double'. Pomona17 (talk) 09:40, 12 September 2008 (UTC)

Disruptions of planets in the habitable zones

I have removed the following passage from the article:

Based on computer simulations, other planetary astronomers consider that any potential terrestrial planets that did once orbit near the stars' habitable zones are now likely no longer located there. The loss, several billion years ago, of these small bodies probably happened during the system's formation. All may have since been ejected by significant disruptions caused by strong gravitational or perturbation effects generated between the two main stellar components.

for which the following were given as references:

1. Croswell, K. (1991). "Does Alpha Centauri Have Intelligent Life?". Astronomy. 19: 28–37. {{cite journal}}: Unknown parameter |month= ignored (help)
2. P.A. Wiegert and M.J. Holman (1997). "The stability of planets in the Alpha Centauri system". The Astronomical Journal. 113: 1445–1450. doi:10.1086/118360. {{cite journal}}: External link in |title= (help)

As far as I can tell the statement is not supported by the references: the Wiegert & Holman paper states that the habitable zone is stable unless the planets have high inclinations with respect to the orbit of the binary stars, and I quote directly from the paper here "Nevertheless, it appears likely that habitable planets could exist within the stable zone as defined here" (p1449). While I cannot access the Ken Croswell reference directly, the sources I have seen that refer to it suggest it states that planets are stable up to about 2 AU from the stars. Thus I consider the passage is unsupported, unless someone can show that the Croswell article says otherwise. Icalanise (talk) 22:30, 7 November 2008 (UTC)

Categories?

Can anyone explain or fix the duplcate category references:-- Mjquin_id (talk) 21:00, 25 January 2009 (UTC)

• HD:128620
• HD:128621
• HIP:71683
• HIP:71681

Of course! Easy! See α Cen A and α Cen B! ... said: Rursus (bork²) 20:38, 29 January 2009 (UTC)

Citation needed about spectrum?

Someone complained that the factbox has G2V + K2IV, while the text has G2V + K2V. That's not a big deal, actually; while texts use to erect this roman number stuff as luminosity numbers, so that K2IV would indicate that α Cen B might be more "evolved" than α Cen A, the luminosity numbers are just a measurement of the general wideness of certain absorption lines up to and including measurement errors. Future measurements might show up that the stars are something like G2.3IV/V + K2IV/V. Or so. ... said: Rursus (bork²) 20:45, 29 January 2009 (UTC)

Actually, as I say below, all literature I've seen describes Alpha Cen B as a Morgan-Keenan spectral class K1 main-sequence star. So, all of a sudden, a star listed as K1V has been bumped to a cooler, brighter spot on the HR diagram. Why? What is the source for that information?

Also, the article states that B is a K1V, not K2. The SIMBAD citation is just a label in a database query, not a scientific paper (or several) arguing why B is subgiant (and not subject to "this roman number stuff").

The Bright Star Catalogue lists G2V and K1V. 68Kustom (talk) 08:59, 10 March 2009 (UTC)

Arcturus

• At −0.27v visual magnitude,[11] Alpha Centauri appears to the naked-eye as a single star and is fainter than Sirius and Canopus.

I have reverted an erroneous edit of this sentence. The editor was not reading it carefully enough. It is discussing the combined appearance of α Cen A and α Cen B. He changed it to the incorrect:

• At −0.27v visual magnitude,[11] Alpha Centauri appears to the naked-eye as a single star and is fainter than Sirius, Canopus and Arcturus.

At -0.27, the combined light from Alpha Centauri does make it brighter than Arcturus at -0.05. It is α Cen A alone, at +0.01 which is fainter than Arcturus, as the very next sentence points out.

The original sentence had it right. B00P (talk) 11:12, 5 March 2009 (UTC)

which is the closest

Alpha Cet is having long history of being considered the closest star to Sol. OTOH Proxima is considered to be closer. Right now the list Nearest stars refers the latter as being closer but the preambles of both articles claim supremacy. IM(ns)HO this has to be resolved, and the controversy explained in more detail. --85.187.29.139 (talk) 12:25, 9 March 2009 (UTC)

The article says this "Alpha Centauri is the closest star system to the Solar System, ...". This is correct. The system is the closest to us. There are three stars in the system and Prox is the closet star to us. This is also correct. I think the confusion comes from the fact that the star names AlphaCetA and AlphaCetB are commonly confused with the AlphaCet system name. HumphreyW (talk) 13:07, 9 March 2009 (UTC)

Alpha Cen B is now a K2IV?

I was surprised to see that Alpha Cen B was recently re-listed here as a K2 subgiant. The only source appears to be the SIMBAD site. I haven't come across any news anywhere that Alpha Cen B is a K2IV; it's always listed as K1V.

There should be reports from a fair number of sources before changing it here. The star is after all rather less massive than Alpha Cen A, but they're the same age. A low-mass K main sequence dwarf couldn't evolve faster than its more-massive G2V sibling. So simply stating that A Cen B is a K2IV turns current stellar evolution theory on its ear.

My guess is that it's a typo at SIMBAD. 68Kustom (talk) 06:39, 10 March 2009 (UTC)

You're right, that is a mistake, alpha Cen B is certainly a main sequence star. The SIMBAD spectral type comes from Gray et al (2006), as you can see on the SIMBAD page, and that paper has an electronic table which contains the typo. I will email Richard Gray to let him know. Well spotted! Timb66 (talk) 23:49, 10 June 2009 (UTC)

I have contacted Richard Gray and he advises that K2 IV is not a typo, but that the classification was affected by the greater-than-solar metallicity of this star. He says that "it is clear the abundances are enhanced over solar, and in the K-type dwarfs this can affect the luminosity criteria and make the star appear evolved. We had to select the classification that gave the best description of the spectrum and let it go at that." So that is cleared up, and I suggest the more common V classification is allowed to stand here. Timb66 (talk) 00:40, 23 June 2009 (UTC)

How a lead (and structure/sections) should go.....

Right then - this is what wikipedia has established as guidelines for its lead sections --> Wikipedia:Lead section.

Arianewiki, if you have a look at all recent Wikipedia:Featured articles, you will note they have a lead thus. The idea is that the lead can be read as a potted summary without delving further into the article. Your view on what a lead should be is yours, while the consensus has decided the other way.

Can you look at the criteria on how things are written and see?

Actually I would have been quite happy to remove all the sci-fi stuff from the lead, rather than a wholesale revert.

Also - look at Wikipedia:Featured article criteria point 2 (b) - headings and subheadings which this now lacks - this (your) version has bits of material on the system in sections 1,2, 5, and 6. It has observation material scattered in 3,4 and 7 and 8. It moves back and forth between connected material.

I do appreciate the amount of work you have put in and was intending to try and work with you to get this to Good and Featured status, but hadn't seen you active in some time.

I was working through some of the exchanges above. No-one owns any article here.

First thing is to get a consensus on preferred order. The version you prefer just jumps too much over the place. Casliber (talk · contribs) 20:28, 6 August 2009 (UTC)

Merge from Gliese 559 A and Gliese 559 B

The following discussion is closed. Please do not modify it. Subsequent comments should be made in a new section. A summary of the conclusions reached follows.

Done. -- Icalanise (talk) 09:42, 4 July 2010 (UTC)

---

I propose the articles Gliese 559 A and Gliese 559 B are merged into this one and replaced with redirects: most of the material in them (if not all) is covered in this article anyway. Icalanise (talk) 09:52, 3 July 2010 (UTC)

I second the merge proposal. -- Kheider (talk) 15:40, 3 July 2010 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

How far apart are A and B, if known?

If not known, the aricle should say so. Although maybe I just missed the part where it talks aout that.-Rich Peterson24.7.28.186 (talk) 07:12, 4 March 2011 (UTC)

Read about it in the binary system section. HumphreyW (talk) 09:16, 4 March 2011 (UTC)

thanks, don't know why i didn't see that.-Rich24.7.28.186 (talk) 06:09, 27 March 2011 (UTC)

Clarification needed

"...13,000 astronomical units (AU), equivalent to 400 times the size of Neptune's orbit." Does 'the size of the orbit' mean 'the (average) radius of the orbit' which, for Neptune, is 30 AU (on average)? — Preceding unsigned comment added by 85.103.7.155 (talk) 15:54, 28 April 2012 (UTC)