Birthday wishes to the Hubble telescope, which is about to turn 21. This magnificent (newly released) photo is of galaxies UGC1810 above, and UGC1813 below, which are close enough to have distorted each other over many millions of years. The spiral arm of the upper galaxy has been dragged out, while the tip of the lower one has been smudged.
Hubble is our first orbiting optical telescope, and it has been hugely successful over the years. This is despite a huge error made during manufacture, in which the mirror was incorrectly ground. This flaw was only detected after it began operation, so was too late to do anything about the mirror. In the end, the clever boys at NASA used software tricks to to process the images, to the point where they are now fabulous images.
Hubble has been serviced a number of times by shuttle missions, to replace various bits and pieces, but is due to be retired in 2014. It is to be replaced with a next generation space telescope known as the James Webb Space Telescope.
Virtually all of the pictures taken by Hubble are available in the public domain – you can visit the extensive gallery here.