Oct 19, 2011
At about one o'clock in the morning of July 1, 2011, Manuel Claro pointed his camera up at the night sky above Alentejo, Portugal, and opened the shutter for 30 seconds. Then he did the same thing again and again and again, 430 exposures over the next four hours, and combined all the images to create this picture.
During each 30-second exposure, the earth rotated a little, while the stars pretty much stood still (by comparison). So the image of each star is smudged as the camera moves a bit; when all 430 of the smudges are shown together in a single image, we see what looks like startracks but is actually a single earthtrack, circling Polaris, the North Star.
The different colors of the different startracks reflect differences in temperature of the various stars.