Wanting to catch a look at last night’s lunar eclipse, I found myself wondering whereabouts it would be in the sky so I knew which window to look out of. None of the news articles I found gave that information, so I decided to calculate it. A question came up.
According to my ‘Personal Weather Station’ gadget, moonrise tonight is at 18:08, and moonset at 07:21 (both GMT, and based on a Newcastle-upon-Tyne location, which is close enough). If my arithmetic’s correct, that means an elapsed time of 13h13m. Sunrise, however, is at 07:18, sunset at 17:23 - a difference of 10h03m. Now, that sounds reasonable at this time of year.
Since I’m obviously missing something obvious, and my brain seizes up every time I try to imagine what’s happening here, could someone please explain in simple terms why this difference?
And no, I didn’t see the eclipse. Damn the clouds and damn light pollution. Why have all those streetlights on anyway? In case some Home Secretary wants a kebab? This ain’t Peckham.
First of all, the moon is travelling “eastward” across the sky during the night, so it always takes longer to travel from East to West than the sun does for that reason alone. Almost a half-hour each night, IIRC.
Secondly, the sun’s position in the sky in Winter is why it takes less time than 12 hours; for the same reason, the moon’s position in the sky right now causes it to take more than 12 hours. You will note (if you could see it) that the moon is fairly far “north” in the sky.
The seasonal variation of the day length in a given location depends on the orientation of the earth’s rotational axis relative to the plane of the earth’s orbit around the sun, the variation of the moon’s up time n a given location on the orientation of the earth’s rotational axis relative to the plane of the moon’s orbit around the earth.
Very observant of the OP. This reply is on the money. The short answer is this: When you looked at the full moon last night, you were looking at where the sun will be in one of the summer months. - Jinx