While looking at the daily forcasts for the week on The Weather Channel app on my phone I noticed that today, Thursday the 18th, both moonrise and moonset are roughly half an hour to an hour BEFORE sunrise and sunset. I also noticed that the day after, Friday the 19th, that moonrise is roughly 15ish minutes before sunrise where as moonset is roughly 30ish minutes AFTER sunset. This weekend, starting Saturday, is when both moonrise and moonset are after sunrise and sunset, with moonrise being just shy of half an hour after sunrise and moonset being about an hour and a half after sunset on Saturday. With Sunday moonrise being just barely an hour after sunrise and moonset being two and a half hours after sunset. Can anyone explain this to me please?
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$\begingroup$ It's hard to understand from your question what it is you're confused about. The moon's motion can seem quite tricky since it's moves considerably just in one day, about 11 degrees on average. The Earth's axial tilt and your latitude also play a massive role in rise and set times, just like they do for the Sun. $\endgroup$– Greg MillerMay 18 at 14:59
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1$\begingroup$ I would put the daily motion at a little over 12 degrees on average. You need to go 360 degrees in the synodic period of 29.5 days. $\endgroup$– Oscar LanziMay 18 at 23:26
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2$\begingroup$ You seem to be asking two different questions. (1) Why does moonrise change from earlier than sunrise to later than sunrise? That is answered below - the Moon orbits the Earth and passes the Sun at New Moon. (2) Why is the time between moonrise-to-sunrise different than between moonset-to-sunset? That is more complex. See the question The moon rises at a different time each day, but that difference changes. Why? (astronomy.stackexchange.com/questions/48591/…) $\endgroup$– JohnHoltzMay 21 at 1:00
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1 Answer
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While one sunrise to the next is about 24 hours, one moonrise to the next is about 24 hours and 50 minutes. The extra 50 minutes are due to the Moon's orbit about the Earth. It therefore shouldn't be surprising that there are days where moonrise occurs shortly before sunrise and moonset occurs shortly after sunset.
answered May 20 at 13:05