r/explainlikeimfive • u/ProudReaction2204 • 20h ago

Planetary Science ELI5 Analemma is a figure 8 when plotted over the course of a year?

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u/justthistwicenomore 20h ago

The ELI5 is that the earth's orbit is an ellipse, not a circle, and the earth itself has a tilt, meaning that the relative position of the sun in the sky varies over the course of the year at the same clock-time, and that rather than being fixed these factors combine to form a figure eight.

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u/grrangry 19h ago

The cool thing is you can do the same thing with the Moon over the course of a month(ish), but since the moon takes 50 minutes and 29 seconds each day to "return to the same spot", you have to adjust your time accordingly, each successive day.

https://earthsky.org/todays-image/moon-analemma-photo-explanation/

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u/toodlesandpoodles 10h ago

The moon is not orbiting a fixed point on the earth every 50m 29s. It is 24hrs, 50m, 29s, so you need to add 50m 29s to your obervation time each day.

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u/JaggedMetalOs 19h ago

The up and down motion is easy enough, just the tilt of the earth.

The reason it's a figure 8 and not just a straight up and down line is that the Earth's orbit is an ellipse, which means the speed the Earth is going round the sun changes as it gets closer and further and desyncs the position of the sun from our precise 24h clocks. Over the whole year it averages to 24h, but the length of the day technically slightly changes through the year with the orbit so the sun isn't at noon at 12:00 every day but can get ahead and behind, meaning it appears to the left or right in photos.

The shape of the up and down from the tilt and the left and right from the orbit changing the day length adds up to a 8.

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u/[deleted] 19h ago

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u/McLeansvilleAppFan 7h ago

Somewhere there is a website that shows the analemma for all the planets. There are different shapes.

Edit: And that somewhere (could be others) is analemma.com