Science Questions

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

Sat, 20th Oct 2012

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Alan, Milton Keynes asked:

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 oíclock in the morning the moon is low in the east. I was just wondering how that worked out?


Chris -   Well, letís zoom out for a bit and imagine you're off of the Earth and youíre looking at the Earth and the moon from space.  So you have the Earth as the bigger of the two bodies sitting letís 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 moonís orbit, the Earth is turning and the Earth takes 24 hours to do a complete circle.  So therefore, as the Earth turns then itís 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, itís all to do with where we are in that so-called lunar cycle which takes 28 days.


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