Difference between revisions of "2172: Lunar Cycles"

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
(Explanation: astrology does not work)
(Explanation: wikipedia:Slim-fit pants)
Line 31: Line 31:
 
**A [[wikipedia:harvest moon|harvest moon]] is full moon closest to the autumnal equinox, possibly orange.
 
**A [[wikipedia:harvest moon|harvest moon]] is full moon closest to the autumnal equinox, possibly orange.
 
**The [[wikipedia:Golden Age of Television|Golden Age of Television]] is said to have occurred in the 1940s and 50s, and the 2000s.
 
**The [[wikipedia:Golden Age of Television|Golden Age of Television]] is said to have occurred in the 1940s and 50s, and the 2000s.
** A [[wikipedia:blue moon|blue moon]] is the extra full moon in years with 13 full moons. An event that occurs once every two or three years. Blue moons don't look any different from regular full moons.
+
**A [[wikipedia:blue moon|blue moon]] is the extra full moon in years with 13 full moons. An event that occurs once every two or three years. Blue moons don't look any different from regular full moons.
 
**There are no occurrences of '''super blood moon''', '''dire moon''' or '''pork moon''' in the Google Books N-Gram viewer, which includes many works from the 1800s through 2008. A [[wikipedia:blood moon|blood moon]] refers to the moon during a lunar eclipse.
 
**There are no occurrences of '''super blood moon''', '''dire moon''' or '''pork moon''' in the Google Books N-Gram viewer, which includes many works from the 1800s through 2008. A [[wikipedia:blood moon|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.
+
**While the popularity of '''skinny jeans''' ([[wikipedia:Slim-fit pants|slim-fit pants]]) does change over time, the idea that this is connected to a lunar cycle is also a joke.
 
*The '''{{w|Antikythera_mechanism|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."
 
*The '''{{w|Antikythera_mechanism|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."
  

Revision as of 09:07, 7 July 2019

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

Ambox notice.png This explanation may be incomplete or incorrect: Created by a MOONBOT. Joke cycle explanations need to be expanded and title text needs to be explained. Do NOT delete this tag too soon.
If you can address this issue, please edit the page! Thanks.

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

  • Nodal precession: The Moon's orbital plane is tilted slightly compared to the Earth's orbital plane around the sun (the ecliptic). This tilt is why we don't constantly see eclipses; most of the time, the Moon's orbital plane is tilted higher or lower than the Sun, so they generally don't cross each other. The two points at which these planes do cross are called lunar nodes. Nodal precession is the gradual rotation of these nodes over time, which for the Moon follows an 18.6 year cycle.
  • Apsidal precession: All orbits have two points where the orbiting body is either closest to, or furthest away from, the thing they are orbiting. These points are called apsides, and the imaginary line between them is called the line of apsides. Apsidal precession is the gradual rotation of this line over time, which occurs in cycles of around 8.9 years for the Moon.
  • Phase: Lunar phase describes the change in shape of the sunlit side of the Moon as viewed from the Earth's surface, which is caused by the changing angle between Moon and Sun as the Moon revolves around the Earth. The cycle of lunar phases takes 29.5 days, a figure referred to as the synodic month.
  • Distance: Because the Moon's orbit around the Earth is elliptical, its distance from the Earth varies slightly over the course of an orbit. This means that the moon's distance also follows a cycle which is the same as the length of one lunar orbit: approximately 27.5 days. This figure is referred to as the sidereal month. Note that the synodic month is (perhaps counterintuituvely) two days longer than the sidereal month - or to put it another way, it takes 2 more days for the Moon's phases to cycle than it does for the Moon to go around the Earth. This is due to the fact that the Earth is also moving around the Sun while the phases are going on, which means that the Moon has to spend 2 extra days "catching up" to the point at which the lunar phase cycle can restart.
  • Earth-Moon relative size: This is a joke cycle; the Earth and Moon do not change size, nor does the Moon ever become larger than the Earth. This may be playing on the idea that the Moon often appears to change size due to a various factors; most commonly, this is due to the Moon illusion, which tricks the brain into perceiving the Moon as much larger than it really is. There are also so-called supermoons, which occur when the full moon coincides with the Moon's closest approach to Earth; these actually do increase the Moon's apparent size, although by a relatively insignificant amount.
  • Lunar shape: Again, this is a joke cycle; the Moon does not actually change shape. A shape intermediate between circle and square is known as a squircle, a subclass of the superellipse.
  • Lunar mood: The moon does not have a mood, although humans can have moods that fluctuate over time, sometimes with a regularity akin to a cycle. 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 diagram shows many different cycles superimposed on each other, highlighting areas where several cycles are coinciding. This is likely satirizing the media trend of overhyping astronomical coincidences and giving them grand-sounding names (which get longer and more impressive the more cycles are coinciding).
    • Supermoon: see 1394:_Superm*n.
    • 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 actually work but occasionally seems to by coincidence.
    • A harvest moon is full moon closest to the autumnal equinox, possibly orange.
    • The Golden Age of Television is said to have occurred in the 1940s and 50s, and the 2000s.
    • A blue moon is the extra full moon in years with 13 full moons. An event that occurs once every two or three years. Blue moons don't look any different from regular full moons.
    • There are no occurrences of super blood moon, dire moon or pork moon in the Google Books N-Gram viewer, which includes many works from the 1800s through 2008. A blood moon refers to the moon during a lunar eclipse.
    • While the popularity of skinny jeans (slim-fit pants) does change over time, the idea that this is connected to a lunar cycle is also a joke.
  • 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.]



comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!

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)