# Talk:Longitude of the ascending node

Active discussions
WikiProject Astronomy (Rated Start-class, Mid-importance)

## Untitled

Can someone please explain how Earth has acquired an ascending node? How does it pass through the plane of its own orbit? 142.177.19.31 05:48, 24 Aug 2004 (UTC)

I wondered that myself. I assumed it was because these numbers are for Epoch 2000.0. There's a discussion on one of these boards about it, I forgot which one. Now, what is the difference between the right ascension of the ascending node and the angle between the first point of Aries and the ascending node? I agree your wording is probably clearer, but I don't think there's a technical difference between the two values. I originally got the data from RedShift, and it stated that the right ascension is defined as the angle between a position and the first point of Aries on the celestial sphere. As long as it is assumed the celestial sphere is projected from the sun, the two seem identical.

Edsanville 16:58, 24 Aug 2004 (UTC)

While the Earth does pass through it's own orbital plane for reasons mentioned above and others, that is not the answer to your question. The reference nodes are the intersection of two planes. One being the Earth's equator and the other being the Earth's orbit. The two are tilted about 23 degrees to each other. The ascending node is where the satellite crosses the equator from south to north measured from one of these nodes, the "First Point of Aries." James65.pike (talk) 20:41, 8 July 2011 (UTC)

The question being asked here is kind of unclear. The Earth has an ascending node, which it crosses once per year. This is a result of its orbital plane is not being perfectly aligned with the Sun's equator, and the intersection of these two planes (Earth orbital and Solar equatorial) define the two nodes. These crossings occur on the vernal and autumnal equinoces, and are the modern basis for the Earth-Centered Inertial reference frame. The First Point of Aries is an obsolete term for the vernal equinox, since this same direction once pointed to the constellation Aries. The Earth doesn't pass through it's own orbital plane, since this is by definition impossible: the orbital plane is defined by the orbit of the body, and therefore, all possible positions of the body are in the plane. siafu (talk) 21:29, 8 July 2011 (UTC)
Well OK, perhaps I was answering the wrong question. If you are wondering why the Earth's inclination is not zero then the answer is basically as Edsanville answered. The two reference planes are constantly changing. That is to say the Earth's orbital plane is not fixed and neither is the Earth's equator. The Earth's orbit is altered by the planets and it also precesses around the Milky Way's axis. The Earth's rotation is also altered by nutation and precesses around our orbital axis. When you pick a reference frame your have to pick a specific time for the ecliptic and the equator. You may also pick mean or true values. Anyhow the Earth's orbit will be different at any other time and therefor will have a non-zero inclination as well as an ascending node. That is to say that the Earth's inclination at one point in time will be different from it's inclination at another point in time. James65.pike (talk) 22:22, 8 July 2011 (UTC)

I don't think Edansville is correct. On Earth's wiki page, the longitude of ascending node is defined relative to "J2000 ecliptic." It has nothing to do with the solar equator there. The inclination is given relative to a few different planes. The current inclination of Earth's orbit is defined as 0.00005° relative to Earth's J2000 ecliptic. So, the long. of asc. node is indeed defining the point where Earth's current orbital plane passes through its orbital plane at J2000. Given this, the LOAN doesn't really tell you anything about the current or past equatorial plane and therefore nothing about current equinox. It only is used to describe how the orbital path of Earth is changing over time. We just need a convenient place to call 0°. --Bt1159 (talk) 14:11, 24 September 2019 (UTC)

## Applicability to exoplanets?

I've asked for some clarification of how the concepts described here apply to exoplanets on the argument of periapsis talk page. AldaronT/C 03:28, 24 July 2009 (UTC)

## First point of Aries

Picking up where the first topic left off, do serious astronomers use this term anymore? Isn't the first point of Aries the same as RA 0h0m0s in the (J2000) celestial sphere? (Tell me if there's a more succinct name for this.) If yes to both, then would anyone be opposed to me changing this? Even if the first point of Aries is used colloquially, I feel that it is confusing for people like me who are not acquainted with astronomy lingo. — Elliot Winkler 03:21, 3 September 2012 (UTC)

The answer is no, astronomers don't really use this term any more. It's usually just called the equinox. First point of Aries is really a holdover from astrology. Tfr000 (talk) 02:10, 27 November 2015 (UTC)

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