Star Trails Over Vienna - 7/14/05

Comments and questions about the APOD on the main view screen.
smita
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Star Trails Over Vienna - 7/14/05

Post by smita » Thu Jul 14, 2005 10:58 am

Hello,
I am newbie, but how would these trails be so perfectly circular, given that the earth also rotates around the sun. Or can please anyone explain why?
Thanks.
Smita

http://apod.nasa.gov/apod/ap050714.html

makc
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Post by makc » Thu Jul 14, 2005 2:57 pm

it's only 1/365 of an orbit, that's less than 0.3% - how much distortion you would expect? consider also that even if you would suddenly appear on the other side of the sun, only few nearest stars would change their position considerably. try looking at the mountain, or distant building, and walking in 2-3m circle at the same time - how much would it change its image in your eye? same with photo.

ahuffman
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Post by ahuffman » Thu Jul 14, 2005 5:13 pm

Would not a single exposure of such a picture be possible above the Arctic Circle in winter?

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Orca
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Post by Orca » Fri Jul 15, 2005 10:11 pm

If you are asking why do the star trails appear circular, it's because the camera was focused directly on the pole star.

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Orca
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Post by Orca » Fri Jul 15, 2005 10:14 pm

ahuffman wrote:Would not a single exposure of such a picture be possible above the Arctic Circle in winter?
:?:

A single exposure? The issue is the length of the exposure. The longer the shutter is open, the longer the star trials.

gak
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Post by gak » Sat Jul 16, 2005 1:53 am

Would not a single exposure of such a picture be possible above the Arctic Circle in winter?
During the Winter solstice ( http://en.wikipedia.org/wiki/Arctic_Circle & http://en.wikipedia.org/wiki/Winter_solstice ), the sun will be below the horizon for at least 24 hours.

I'd say you'd be able to do a 24 hour exposure shot like this... assuming the sun is low enough so it won't affect the brightness of the sky too much. You'd be quite a keen person to do this though :)

Gerald Kaszuba