Wikipedia:Reference desk/Archives/Science/2023 June 27

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June 27

Butterfly ID

What species is the swallowtail butterfly on the lower left at 0:54 in this music video: https://www.youtube.com/watch?v=yvGhqLV_iSg?t=54 ? Is it a subspecies of Papilio menatius, or is it another species? (Pictures OK as long as they're not crazy big -- this species does not scare me, because it lacks the vertical stripes of P. glaucus and its closest relatives). 2601:646:9882:46E0:A14E:5F98:D605:3099 (talk) 09:42, 27 June 2023 (UTC)

Could be a distorted image of the straight-banded swallowtail, Papilio paeon, or one of its close relatives. Abductive (reasoning) 10:09, 27 June 2023 (UTC)

Or maybe not distorted but just differently-proportioned -- with nymphalids and swallowtails, there's a high degree of intra-species variability in terms of proportions, with one extreme being what I call the "bat" or "boomerang" shape (long narrow forewings, small hindwings, an overall triangular or rhomboidal shape -- which is what you see in the video), and the other being the "cloverleaf" (both pair of wings about the same size, which is how butterflies are classically depicted and what you see in the picture in the article). Is that not a possibility? 2601:646:9882:46E0:C84B:94AF:7EB4:1347 (talk) 03:09, 29 June 2023 (UTC)

Moon phases

Does every place in the world see same moon phase in any given time? Or it is possible to have full moon in one side of the world and new moon on the other? --40bus (talk) 14:00, 27 June 2023 (UTC)

Yes, everyone sees the same phases of the Moon. People north and south of the equator do see the Moon's current phase from different angles, though. If you traveled to the other hemisphere, the Moon would be in the same phase as it is at home, but it would appear upside down compared to what you're used to! - from NASA - Top Moon Questions Alansplodge (talk) 14:14, 27 June 2023 (UTC)

I find it astonishing that instead of simply answering the question ("Yes, everyone sees the same phases of the Moon.", good) and explaining why that is (the phases of the Moon are determined by the positions of Sun and Moon relative to Earth, and these relative positions are (almost) identical for everyone on Earth given that the planet is much smaller than the distances to either Sun or Moon) the good folks at NASA insist on obfuscating and confusing the answer by an elaborate but barely relevant sidenote, which they don't even get entirely right (the thing about the equator − should be the latitude that corresponds to the current declination of the Moon, which can vary between –28° and +28° or so)... --Wrongfilter (talk) 14:30, 27 June 2023 (UTC)

They added TMI, maybe. Meanwhile, the notion of one side of the earth seeing new moon at the same time the other side sees full moon is pretty funny. The moon would have to orbiting the earth a lot more frequently than once a month! ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:03, 27 June 2023 (UTC)

As is the talk of "the dark side of the moon" [1]. As if one side was bathed in perpetual sunlight and the other experienced perpetual night! 80.43.83.113 (talk) 16:11, 27 June 2023 (UTC)

Yes. At new moon, the "dark" (hidden) side is "full". ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:46, 27 June 2023 (UTC)

Quoting from our article Far side of the Moon:

The hemisphere has sometimes been called the "dark side of the Moon", where "dark" means "unknown" instead of "lacking sunlight"

It is the side humanity was, until recently, in the dark about.  --Lambiam 12:09, 29 June 2023 (UTC)

The "upside down" statement is relevant for people who speak French and have been taught the mnemonic  ◗  = p = premier quartier,  ◖  = d = dernier quartier.  --Lambiam 13:21, 28 June 2023 (UTC)

The German variant of that uses  ◗  = 𝔷 = 𝔷unehmend,  ◖  = 𝒶 = 𝒶bnehmend. That form of cursive z is hardly used any more, though.--Wrongfilter (talk) 13:58, 28 June 2023 (UTC)

It's also relevant if you imagine that the moon looks like a face in the northern hemisphere, the "face" is upside-down in the southern hemisphere. Dhrm77 (talk) 15:14, 28 June 2023 (UTC)

When the moon culminates to the north of the zenith — which can happen in the northern hemisphere as well. Still not relevant to the question, though interesting. Anyway, I've got to get out before the moon falls. --Wrongfilter (talk) 15:28, 28 June 2023 (UTC)

The way I was taught back in the 1960s was to consider the way you hand wrote the letter "x" in algebra (I've tried searching UTF-8, but can't find the glyph, best I can do is ")(" which gives an idea of what I mean). The lefthand arc was the first, so that was the first quarter of the moon, the righthand arc was last, so that was the last quarter of the moon. Martin of Sheffield (talk) 09:24, 29 June 2023 (UTC)

The difference between what one end (say most eastern side) see compared to the other (most western side), is so small, it's not significant. Dhrm77 (talk) 16:36, 27 June 2023 (UTC)

If I understand correctly the difference is 1 degree. Not insignificant when dealing with new moon. Zarnivop (talk) 22:15, 27 June 2023 (UTC)

It's 1 degree from center to edge, parallax always seems to be given that way for some reason. The New Moon isn't really visible at less than 7 degrees from the Sun (center-to-center, another astronomical convention) but they've taken pictures in non-visible wavelengths with a shaded telescope at 4 or 5 degrees — enough to see the closest the Moon ever got to the Sun that New Moon. Sagittarian Milky Way (talk) 02:06, 28 June 2023 (UTC)

Your can also look at lunar parallax. Ruslik_Zero 20:49, 27 June 2023 (UTC)

You don't actually need French to use that mnemonic - the meaning of premier is well understood in English, and dernier is the other one. This is how I knew it, but my mother said that she recognised a moon approaching first quarter because the horns pointed to the east, where the sun would rise and increase, while after last quarter the horns pointed to the west, where the sun would dip before disappearing. 2A00:23C6:2417:3101:849E:7B53:B9AB:8D4E (talk) 16:20, 28 June 2023 (UTC)

Until comparatively recently, the relevant term was "changes of the moon" and the stages were "first quarter", "full moon", "last quarter" and "change". Then in 1767 the first ever Nautical Almanac was printed at Greenwich (or compiled there) and the reason for the change in nomenclature appears to be this [2]. 2A00:23C6:2417:3101:849E:7B53:B9AB:8D4E (talk) 16:49, 28 June 2023 (UTC)

These uses of "new moon" are quite a bit older: from 1600, from 1618, from 1625. This is, of course, vernacular for Latin nova Luna.^[3][4]  --Lambiam 11:59, 29 June 2023 (UTC)

Among the explanations offered for the phenomenon are:

• The Earth's shadow cast on the moon's surface
• Clouds hiding the moon's surface

and many more [5]. 2A00:23C6:2417:3101:849E:7B53:B9AB:8D4E (talk) 17:05, 28 June 2023 (UTC)

Which phenomenon? The Moon phases? The real explanation is evil spirits eating the Moon by gnawing off the side.^[6]

That came in handy when Christopher Columbus found himself in a bit of a jam March 1504 lunar eclipse. There was another sixteenth century kerfuffle [7], embedded link [8]. The Catholics claimed for 400 years that this document, the Compendium of Aloysius Lilius, was no longer extant and no copies survived, but it was hiding in plain sight. The word used is novilunia, which is ambiguous. There was quite an industry in resolving this [9]. Columbus explored when the Gregorian calendar was but a twinkle in Aloysius' father's eye. The golden number (position of the year in a cycle of 19 years, used to calculate the date of Easter) for 1504 was 4 (a puzzle for you - how often does a year ending 04 have golden number 4?). If you weren't literate like Columbus you would turn to your clog almanac, in which the golden numbers, showing the dates of the new moons, were marked just as they were in the Breviary or Missal. 4 was marked against 18 February.

What! A new moon on 18 February and full moon on the 29th? Impossible! People would look in the missal and up at the sky and say "the breviary is wrong!" and the priests would say "hush". Anyway, when the reformers began planning a change to the calendar a Syrian churchman came to Rome to tell them they were doing it wrong. First, he pointed out that in the new calendar the equinox would wander across three days (19-21 March) and it would be better to copy the Persian calendar, in which it always falls on the same date. Queen Elizabeth's astrologer John Dee identified a longitude in the American colonies ("God's longitude") where this would happen. Meanwhile, people recited a mnemonic while moving a finger up the page of the breviary - nova luna hic or in coelis est hic.

Traditionally, the fourteenth day of the lunar month was the full moon. Until the Syrian churchman intervened, the reformers were going to use their "epacts" to mark the conjunction, rather than the day the new moon becomes visible. From the link you will see that Lilius advanced two proposals - the system we use now in which ten days vanished and a backup (in case that fomented revolution) of taking the ten days by stealth, with no leap days for forty years. How well would Lilius have done in 1504? Well, the golden number was 4 and the epact was also 4 (another puzzle for you - how often does a year ending 04 have both golden number 4 and epact 4?). In Lilius' table epact 4 is set against 25 February. It matters not that 1504 was a leap year and the 25th was ante diem sextum kalendas martias, following ante diem bis sextum kalendas martias. In his theory the leap day simply didn't exist. If we allow for the disappearing ten days he would have placed the new moon on 15 February and the fourteenth day of the lunar month on both the 28th and the 29th (if the 29th is taken as the leap day). 81.135.52.95 (talk) 11:08, 30 June 2023 (UTC)

Is the net atmosphere motion stationary 24/7/365 or is it at least stationary on average?

Relative to the solid crust. Or does the net atmosphere or "the part that touches the non-gaseous surface" or "the part at flight level 350 and 360" (typical cruising altitude) or "the part that's in the troposphere" net rotate slower or faster than the crust or have net latitude increase or decrease when averaged out for decades or at least temporarily?

Maybe by "net angular momentum of the atmosphere" or "ranking each dalton of air by "degrees/miles per second of signed latitude/longitude increase" and finding the mean or median" or maybe there's other measures of central tendency I haven't thought of.

And if you measure by say "square miles of surface" it doesn't even necessarily have to be 50% rise 50% sink to be net stationary in elevation so that the atmosphere isn't expanding or getting closer over the long run. Sagittarian Milky Way (talk) 22:39, 27 June 2023 (UTC)

Try exploring the height, etc. settings (click 'earth ' at bottom left) on this website. {The poster formerly known as 87.81.230.195) 90.197.177.243 (talk) 23:12, 27 June 2023 (UTC)

It beautifully shows the trade winds, mid-latitude westerlies, extratropical cyclones etc, but I don't have a microprocessor in my head to figure out what it looks like with all the square miles ranked from most minus longitude increase per hour to most positive how many degrees per hour is the mean or median square mile? Sagittarian Milky Way (talk) 00:13, 28 June 2023 (UTC)

I model the Earth's atmosphere as a thick-walled hollow sphere of gas mass 5.1480 x 10¹⁸kg. The inner radius 6371 km is sea level where pressure is 1 Bar. Nett angular rotation of the atmosphere is affected by friction with Earth (at sea level only), by the tidal drag (throughout) of the Moon's gravity, and it has no friction with vacuum space. Supposing that tidal drag dominates at altitude 5.5 km where pressure is half a Bar and given that the angular velocity of the Moon is 13.176 degree/day Eastwards, I conclude that the upper half of the atmosphere moves Eastwards at 7.9 km/sec. Philvoids (talk) 10:27, 28 June 2023 (UTC)

7.9 km/sec is 28,440 km/h. Roughly Mach 23 (depending on air temperature). Which would make air travel rather difficult. I think you may have displaced a decimal point somewhere. Even the polar jetstreams (strongest in the southern hemisphere at this time of year) rarely exceed 200 knots (370 km/h) or so, at around 10 km altitude. AndyTheGrump (talk) 11:47, 28 June 2023 (UTC)

Mea culpa! My error was to (mis)apply the formula for a body in orbit: Velocity v = sqrt(GM/r) where G = 6.67x10^-11 m³⋅kg⁻¹⋅s⁻², M = 5.97x10²⁴kg and r = (6371 + 5.5) km. Now much wiser grace to your kind correction, I enlist an angelic bird at altitude (6371 + 5.5) km who eclipses the Moon in my sight and beg to report its velocity as 0.0002 km/s. Philvoids (talk) 14:54, 28 June 2023 (UTC)

The Moon's a lot faster than decimeters per second cause a zenith Moon goes all the way around the world and comes back ~25 hours later. Sagittarian Milky Way (talk) 15:40, 28 June 2023 (UTC)

I cite the lunar month 27 to 29 days and the Moon's angular velocity 13.176 degree/day Eastwards. Philvoids (talk) 22:00, 28 June 2023 (UTC)

The Earth goes ~360 degrees per day eastwards so the Moon goes ~360-13=347 degrees/day west AKA setting and rising. Sagittarian Milky Way (talk) 23:02, 28 June 2023 (UTC)

The jet streams move predominantly eastward and are much more powerful than the trade winds, so I expect the average velocity also to be eastward (relative to the Earth's surface). But I cannot find data that allows me to make an estimate, however rough.  --Lambiam 11:18, 29 June 2023 (UTC)