Blue Flame, Colour photograph (Giclée) by Shane Lamb. Alaskan night sky is dark from August to April. The Aurora is a natural light display caused by charged particles from the sun interacting with the earth's atmosphere. When these particles collide with oxygen, yellows and greens are produced, with nitrogen they produce reds, violets and rarely blues
The night sky is a dark place, with only the moon and stars to cast any light. But throughout the long winters high in the northern hemisphere there are nights that are illuminated with spectacular displays of green and blue light dancing across the skies. We are talking, of course, about the Northern Lights. The Aurora borealis, to give them their proper name.
Located 500 million light-years away in the constellation Sculptor, the galaxy looks like a wagon wheel. The galaxy's nucleus is the bright object in the center of the image; the spoke-like structures are wisps of material connecting the nucleus to the outer ring of young stars. The galaxy's unusual configuration was created by a nearly head-on collision with a smaller galaxy about 200 million years ago.
When the Voyager 1 and 2 spacecraft flew by Saturn in 1980 and 1981, they were able to pay only fleeting attention to Titan, the second largest moon in the solar system (larger even than the planet Mercury) and the only solar system moon with an appreciable atmosphere. These images are from subsequent Titan flybys in 2005 and 2006. - Image credit: NASA / JPL / University of Arizona