Last night during Earth Hour, Ted Dobosz, a good friend, took this lovely image of star trails circling the south celestial pole. In an email to his various astronomical-minded friends, Ted remarked that he took images of the Sydney sky glow during and after Earth Hour (local time: 8:30-9:30 pm) and found that there was no noticeable reduction in Sydney's light pollution. In asking for Ted's permission to use this image to liven up my blog, he supplied some additional information: "Hi Pete, ... It was taken from the rock looking south. It was taken with a Canon 40D at 400ASA for 30 mins at F4.5. The lens was a Tamron 17-55mm and it was taken at 17mm. ... Conditions last night ordinary with a brown haze and 30% reduction on brightness of all objects. ... Ted." The rock is Linda Rock in the Blue Mountains to the west of Sydney, Australia; Sydney is about 100 kms (62 miles) distant. In the image the star trails have obvious colour, and the two pieces of 'fog' at two and five o'clock are the Large and Small Magellanic Clouds, satellite galaxies of the Milky Way.
If you enlarge the image the star colours show more clearly, as does the pale blue of the LMC; the colours are real and indicate the temperature of the star making the trail (red through orange 3-5,000 deg C.; white: 8-11,000; blue: 16-50,000). For the LMC the pale blue indicates that the majority of its stars are young and have temperatures above 16,000 degrees centigrade. As a comparison our sun is yellow indicating that the disk we see has a temperature of 5,900 degrees centigrade. The yellow glow at the bottom left (south-east) is from the Sydney metropolitan area, the fainter glow at bottom (south) originates in the suburbs making up the Campbelltown area.
Unlike the north celestial pole there is no bright pole star. To see an untrailed image at similar scale look at this August 2006 image from Astronomy Picture of the Day.
Image (used with permission): © Ted Doboz, 2009.
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