Why does the moon sometimes appear out-of-place?

21 October 2012





Quite often I go out in the morning and I'm in Milton Keynes, so I would expect the moon to rise in the east and set in the west. Sometimes at about 2, 3, 4 o’clock in the morning the moon is low in the east. I was just wondering how that worked out?


Chris - Well, let's zoom out for a bit and imagine you're off of the Earth and you're looking at the Earth and the moon from space. So you have the Earth as the bigger of the two bodies sitting, let's say, in the centre and the moon is in orbit around the Earth.

So the moon goes around the Earth, and the moon takes a month to do a complete lap of the Earth and get back to where it started: 28 days to do a complete orbit of Earth.

Also, inside the moon's orbit, the Earth is turning, and the Earth takes 24 hours to do a complete circle. So, therefore, as the Earth turns then it's going to see the moon from one side of the Earth go across the sky and then down on the other side. So, you're going to see the moon rise and set. But because the moon is also doing a lap around the Earth, the moon is going to appear at different points in the sky at different times of the day and night. So sometimes the moon will be up during the day.

Alan - So we see the Sun and moon at the same time?

Chris - Exactly; and so it's all to do with where we are in that so-called lunar cycle, which takes 28 days.


Excellent simple explanation of moon movement

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