A few months ago I was in car and noticed moon. You could see bottom half (in crescent shape) but not top half.
How is this possible to look up into night sky and see only bottom half of moon?
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2$\begingroup$ A cloud obscuring the top half? $\endgroup$– jamesqfJul 19, 2017 at 18:19
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$\begingroup$ I can't speak to the processes (I've looked into them and understood them before, but don't work with them enough to be on top of them, certainly not to be comfortable in describing!)... but do have a nice link that will give some credence to what's possible. And found a date with indeed an almost total bottom half crescent: mooncalc.org/#/28.5383,-81.3792,11/2019.12.21/02:38/1/0 The crescent direction doesn't seem to be keyed by time of year, so must have something to do with variations in the earth-moon planes? $\endgroup$– JeopardyTempestJul 19, 2017 at 21:20
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$\begingroup$ I think you need to clarify what you mean by "bottom half". Do you mean half of a crescent (my original assumption), or just a crescent near the horizon, as in this artwork: blogs.discovermagazine.com/badastronomy/files/2011/11/… $\endgroup$– jamesqfJul 20, 2017 at 6:42
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1$\begingroup$ As you can see from the answer, please edit your question and add your location at the time. And do us the courtesy of making a few months ago specific (Yes, we can deduce it from the date your originally asked) $\endgroup$– Jan DoggenJul 20, 2017 at 10:28
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2$\begingroup$ Related: astronomy.stackexchange.com/questions/1539/… $\endgroup$– Jan DoggenJul 20, 2017 at 10:34
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2 Answers
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It depends on the season and even more on latitude.
At any given time, the same side of the Moon faces the Sun. Where you stand on Earth doesn't change which part of the Moon is lit, but if you think about the orientation of people on the earth, people in the Northern and Southern Hemisphere are "upside down" to each other and people on the equator are perpendicular. The Moon doesn't change but the point of view of people on Earth relative to the Earth's surface makes a full 360 degrees of rotation based on latitude, so the same moon at the same time can appear as a left crescent, a right cresent, a boat and a yamaka depending on the person's latitude at the time of viewing.
Also explained here.
And this should probably be astronomy.
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The explanation would be that the sun at that moment was deep below earth's horizon (in other words, at the place the asker was looking at the moon it would probably have been around midnight) and illuminating the moon from that point.
The crescent itself shows the direction from which the sun is shining at that moment. If, keeping looking in the direction of the moon, you had lowered your gaze towards your feet, and you'd been able to see through earth, you would have seen the sun.
