2172: Lunar Cycles

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Lunar Cycles
The Antikythera mechanism had a whole set of gears specifically to track the cyclic popularity of skinny jeans and low-rise waists.
Title text: The Antikythera mechanism had a whole set of gears specifically to track the cyclic popularity of skinny jeans and low-rise waists.

Explanation

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This comic shows a mixture of real, scientific lunar cycles and cycles that are comedic or fictional in nature.

  • Nodal precession: The comic shows that the moon's nodal precession follows an 18.6 year cycle. This is true. What this means is that the points in its orbit where the moon crosses the equator (called the ascending and descending nodes) move westward, taking just over 18.6 years to complete a 360-degree cycle.
  • Apsidal precession: The comic shows that the moon's apsidal precession follows an 8.9 year cycle. This is true. What this means is that the major axis of the moon's orbit - the line between the periapsis (nearest point) and apoapsis (furthest point from Earth) of its orbit - precesses eastward, taking about 8.9 years to complete a 360-degree cycle.
  • Phase: The comic also shows that phase has a 29.5 day cycle. This is true. This is the synodic month. Because the lunar cycle is based on how the sun's light shines on the moon as seen from earth, it is determined by the relative positions of the earth, moon, and sun. Because the earth has moved, very roughly, 1/12 of the way around the sun during a lunar month, it takes extra time for the moon to reach the point where it is is fully lit again, so this is longer than a sidereal month. A synodic month, or the time from one full moon to another, is about 29.5 days as stated.
  • Distance: The comic shows that distance has a 27.5 day cycle. This is true. A sidereal month, which is essentially the time it takes the moon to go around the earth, is approximately this length (although the mean time for a sidereal month may be closer to 27.3 days). Because the moon's orbit around the earth is elliptical and not perfectly circular, with a periapsis of about 362600 km earth-moon distance and an apoapsis of about 405400 km earth-moon distance, the distance to the moon essentially follows this cycle with times of peak distance about 27 and a half days apart.
  • Earth-Moon relative size: The idea that there is a cycle in which the moon becomes larger than the earth is a joke. However, Sun-Moon Relative Apparent Size would be a real thing, with there being times when the sun appears bigger and times when the moon does.
  • Lunar shape: The idea that there is a cycle in which the moon becomes a square and then a circle again is a joke. Mathematically these shapes between a circle and square are a subclass of superellipses called squircles.
  • Lunar mood: The idea that there is a cycle in which the moon becomes happy, then neutral, then upset, then neutral is a joke. Ironically, the section of the graph that shows a good (i.e. happy) mood has the graph line curving up then down like the mouth of a frown, and for the bad (unhappy) mood it curves down and then up, as in the mouth of a smile.
  • The final image shows many different cycles superimposed on each other.
    • Supermoon: see 1394:_Superm*n.
    • Super blood moon: a blood moon refers to the moon during a lunar eclipse.
    • While the popularity of skinny jeans does change over time, the idea that this is connected to a lunar cycle is also a joke.
    • Two-week window in which astrology works. Astrology is a pseudoscience which claims that the positions of the celestial bodies can be used to predict human affairs. This is a joke on how astrology does not work (or rarely works).
  • The Antikythera mechanism mentioned in the title text is an ancient Greek machine, rediscovered in 1901, designed to calculate astronomical positions. The title text jokes that there is a set of gears on said mechanism that is used to predict the popularity of "skinny jeans" and "low-rise waists."

Transcript

Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.
Understanding lunar cycles
Nodal precession
[A diagram showing a broad cosine-like wave with wavelength labelled as 18.6 years. To the right are two diagrams showing an orbital cycle moving in and out of plane.]
Apsidal precession
[A diagram similar to the one above but with a slightly shorter wavelength, labelled as 8.9 years. To the right are two diagrams showing an elliptical orbit around a planet and the same orbit rotated.]
Phase
[A diagram similar to those above with a shorter wavelength, labelled as 29.5 days. To the right is a diagram showing four phases of the moon: New, Waxing crescent, Waxinf gibbos, Full.]
Distance
[A diagram similar to those above with a shorter wavelength, labelled as 27.5 days. To the right is a diagram showing the distance of the moon from the Earth over time, with distances marked by arrows.]
Earth-Moon relative size
[A wave with long wavelength with an arrow pointing to the minimum labelled 'Earth bigger' and an arrow pointing to the maximum labelled 'Moon bigger'. To the right are two diagrams of the moon and Earth, one showing the Earth bigger than the Moon and the other showing the Moon bigger than the Earth.]
Lunar shape
[A wave with long wavelength with an arrow pointing to the minimum labelled 'Circle' and an arrow pointing to the maximum labelled 'Square'. To the right is a diagram showing a circle, a circle transforming into a square with outward arrows at each corner and a square transforming into a circle with inward arrows.]
Lunar mood
[A wave with long wavelength with an arrow pointing to the minimum labelled 'Bad' and an arrow pointing to the maximum labelled 'Good'. To the right are four emojis: :), :|, :(, :|]
[A superimposed graph of all the above waves. Different points on the graph are labelled: Harvest moon, Supermoon, Blue moon, Skinny Jeans popular, Super blood moon, Golden age of TV, Dire moon, Pork moon, Two week window in which astrology works, Total eclipse of the sea.]



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Discussion

Is it just me or is the square-circle moon cycle a reference to Minecraft? EnderPlays: Joined 29 April 2021 (talk) 02:44, 18 December 2022 (UTC)

Is it possible that the size of the Earth and the moon are supposed to be comparisons of how big the Earth looks from the moon vs. how big the moon looks from the Earth? 172.69.170.88 (talk) (please sign your comments with ~~~~)

Why would that have a cycle different from the distance cycle?Barmar (talk) 20:20, 5 July 2019 (UTC)

Where is the total eclipse of the heart? Actually, why do we not have a total eclipse of the hart - when all deer are hidden?

A very quick and dirty (probably flawed, until I can plug things into a suitable visualiser to check and/or improve my initial idea) attempt to describe the nature of the square/circle oscilations of the Moon might well be smething like |r.cos(θ)−r.sin(θ)|.|sin(t/λ)| + |r.cos(θ)+r.sin(θ)|.|sin(t/λ)| + |r.√(2/π)|.|cos(t/λ)|=k ...only then you'd also want to make k a quantity also multiplied by the relative Earth/Moon size cycle. Either way, YMoonMV. 141.101.98.88 00:41, 6 July 2019 (UTC)

Isn't the square/circle a reference to rounded corner rectangles. If you increase the corner radius of a square, enough, you get a circle. SDSpivey (talk) 05:37, 6 July 2019 (UTC)

Does anyone know of a real chart similar to the format of the last panel? That might be a cool thing to link to. 162.158.75.166 16:38, 6 July 2019 (UTC)

Did anyone else expect to see "Total Eclipse of the Heart" right after "Total Eclipse of the Sea"? No? Ah, my coat, thank you.Daemonik (talk) 09:17, 8 July 2019 (UTC)

I refer the honourable gentleman to the answer I gave earlier 162.158.154.67 20:10, 8 July 2019 (UTC)

I remember there being a blue blood supermoon or some crazy thing like that once a year or so back. Mostly because I dreamed that it was also a falling moon and woke up very worried. --162.158.58.169 00:18, 12 July 2019 (UTC)

Astrology

I think this is primarily an astrology joke. Astrologers often use astronomical cycles (both real and made up) to "predict" future events or explain historic events. By having enough cycles, they can usually come up with results like "skinny jeans are always popular whenever the happy moon is in Pices and wet Mars is in the same Chinese zodiac as Mercury".

There's also possibly an allusion to Fourier transforms. 162.158.92.160 (talk) 03:14, July 6, 2019‎ (please sign your comments with ~~~~)

You know, I kind of expected a joke about periods 172.69.160.146 01:49, 10 July 2019 (UTC)

I think this is unlikely - the jokes all hinge on cycles of the moon, and don't reference any dates or other celestial bodies in the way astrology does. 162.158.154.37 12:33, 8 July 2019 (UTC)

Phase x distance and supermoons

I've been absolutely nerd-sniped by the "Phase x distance" in the bottom diagram. As far as I can figure out, if you multiply phase and distance, you should end up with a new cycle with a period of (29.5 x 27.5) = 811.25 days, which is about 2 years. A supermoon is when a full moon occurs when the Moon is closest to the Earth, so this phase x distance figure is effectively a supermoon detector - that's why supermoons occur at the peaks in Randall's diagram.

But when I looked into supermoons a bit - specifically this diagram from Wikipedia - other sources shows supermoons occurring on a yearly cycle - we supposedly get them every year. How can that be the case, if the two lunar cycles only synchronize every 2 years? It seems to me like there has to be at least one out of every two years where we get no supermoons at all - ie. the full moon is always coinciding with the moon being furthest away.

I feel like I must have made a mistake or wrong assumption, but I can't figure out what it is. Hawthorn (talk) 17:15, 6 July 2019 (UTC)

I figured it out; it turns out that I was simply wrong about how to calculate the length of a combined cycle. This graph shows that the two cycles would coincide every 400 days or so. Still can't figure out what "phase x distance" is meant to represent, though. Hawthorn (talk) 17:54, 6 July 2019 (UTC)

Earth/Moon changing size

While I do know that the Earth and Moon can technically change size due to accretion of interstellar material, the amount is so negligible that I don't even think it's worth mentioning. I suspect the Earth changes size more from thermal expansion and contraction than from accretion. Hawthorn (talk) 13:03, 9 July 2019 (UTC)

Harvest Moon

The harvest moon does have some astronomical significance: the time of moon-rise from day to day changes less around the harvest moon than at any other time of the year. Wikipedia and its source say that this allowed harvest work to continue into the night during the days after the full moon without a significant period of darkness between sunset and moon-rise. 172.68.189.85 05:59, 10 July 2019 (UTC)