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It would have been possible roughly to estimate the 30-seconds
exposure-length of this beautiful photo by measuring the star trails.
If you look closely at the brighter stars in the top right corner and
especially the top left, you can just see that they are slightly
elongated. These short trails form concentric circles, with their
centres near the top of the auroral glow, in the middle of the photo.
As the earth turns, the sky rotates around a point close to the Pole
Star. Judging from the trails, it might be one of the stars visible
just above the cloud. The photographer was clearly facing due north.
http://antwrp.gsfc.nasa.gov/apod/ap060906.html[log in to unmask] * http://www.interactives.co.uk
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Give people facts and you feed their minds for an hour.
Awaken curiosity and they feed their own minds for a lifetime.
*
Ian Russell
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