The Moon (166 views)

[eric]

i.imgur.com/DLZCwjB.mp4

i charted how long the moon was in the sky over porto portugal from may 2016 to present and looked for patterns for N day cycles (thanks timeanddate.com!)

the moon turns from new to full in 29.5 days

22 days is nothing. 22 days has nothing to do with anything

and yet, there is clearly a 22 day cycle of some kind in the length of moon-days

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another weird thing, here's all the data

i.imgur.com/ehs7IBV.png

the longest moon-days are getting longer, the shortest moon-days are getting shorter

the distance from the moon to the earth is changing over time, but not that much over a five year period. i'll keep looking

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do either of these have to do with each other?



keep a weather eye on the moon, boys

[Yawn of the Dead]

Yeah but how long is the moon over my hammies

[Deleted]

It takes 27 days, 7 hours, and 43 minutes for our Moon to complete one full orbit around Earth. This is called the sidereal month, and is measured by our Moon's position relative to distant “fixed” stars. However, it takes our Moon about 29.5 days to complete one cycle of phases (from new Moon to new Moon). This is called the synodic month. The difference between the sidereal and synodic months occurs because as our Moon moves around Earth, the Earth also moves around our Sun. Our Moon must travel a little farther in its path to make up for the added distance and complete the phase cycle.

[eric]

Here are twenty years of lunar days over the skies of Porto, Portugal, and a zoom in for detail on the rightmost section:



There is clearly a periodicity here, but it's also really really long. First let's try to find that small period and see if that gets us anywhere…

i.imgur.com/cKwfSDp.mp4

Alright! Now let's look at just the max and min of each 26.4 day cycle and see how long it takes to line back up again…

i.imgur.com/40KDgo8.mp4

So if we go 26.4 * 250 = 6600 days apart, our graphs look like…

i.imgur.com/uvXNLv7.mp4

They line up almost exactly! 🥳 …but why? What does 6599 days have to do with anything? Well, it turns out that 6585 days is an extremely important number in lunar geometry because if there's a lunar eclipse on any given day, there will be another one 6585 days later. Put another way, due to the tilt of the earth and the tilt of the moon's revolution around the earth, it takes 6585 days from any given point in time for them to get back in the exact same alignment. O.K. but why 6599 and not 6585?

I don't know 😄

And why did we get such a cool pattern at 22? It divides into 6600 and more importantly 6600/6 (since Excel uses a six color palette and just keeps taking them in order) but so does 25 and that didn't look cool. Let's just do multiples of 22 and see what happens!

i.imgur.com/DfDFPyz.mp4

Aha! Maybe 264 was the key, let's see what happens around 13!

i.imgur.com/oPPj5Ss.mp4

This doesn't tell us anything but it IS cool looking!

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Next I'm going to repeat this experiment with data from the shores of northern Oslo. We know at higher latitude the extremes of solar days are more pronounced, will we see the same phenomenon in lunar days?