# The Moo7 - difficult to see the stars close to the Moon but...

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The Moon How long does it take the Moon to orbit once around the Earth? It takes about 27.3 days. Why not 29.5 days (the time for the phase cycle)? Again, it has to do with the fact that the Earth is moving around the Sun. Take a peak at Figure 10. It shows the variation from one Full moon to the next. Remember, the Moon has to be in a straight line with the Earth and Sun for it to be Full. It starts out lined up with the Sun, but after 27.3 days, the Moon will have made one complete orbit of the Earth (again be located to the left of the Earth). At this time is it Full? No, because it is not in a perfect line with the Sun. You have to wait about 2 more days for it to again be aligned with the Sun and for it to be Full again. If you spend a couple of days watching the Moon relative to the stars you'd see that it moves about 12 degrees each night (since it has to go 360 degrees in about 30 days). You may not notice the motion of the Moon relative to the stars over the course of an evening since it is sometimes
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Unformatted text preview: difficult to see the stars close to the Moon, but you can certainly note the fact that each night it rises about 50 minutes than the previous night, so the Moon's position relative to the stars has changed. Figure 10. The Moon makes one complete orbit of the Earth in 27.3 days, but it will not be again Full until a total of 29.5 days has passed. One orbit of the Moon takes 27.3 Days. This would be the Moon's Sidereal Period since it is the time for the Moon to be back in the same location relative to the stars, and this is also the time for one orbit. How long does it take for one rotation (spin) on its axis? Does the Moon actually spin on its axis? If you said "no," then you're wrong. The Moon does spin on its axis, but it does it in 27.3 days. That's the same amount of time for one orbit - what does that mean? It means that one side of the Moon always faces the Earth - that the Moon has one side tidally locked with the Earth....
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## This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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