Canadarm and the Seven Sisters
Credit: Don Pettit, ISS Expedition 6 Science Officer, NASA
Explanation: Sometimes a picture is worth a thousand words.
International Space Station (ISS) science officer Don Pettit took this one on January 18, 2003. In the foreground is the space station's Canadian-built robotic arm, "Canadarm", which helps astronauts with construction of the growing ISS. Just above Canadarm's elbow are the Pleiades, also known as the Seven Sisters. These seven stars, arranged like a little dipper, are just the brightest members of a cluster of more than 3000 stars lying 400 light years from Earth.
Between Canadarm and the Pleiades is Earth itself. Below, the cloudy landscape is lit by a nearly-full Moon (off camera). Above, the edge of Earth's atmosphere is defined by a layer of glowing air--a brownish-yellow band of light stretching all the way across the image. Airglow is caused by chemiluminescent reactions in Earth's nighttime atmosphere. The reactants are atoms and molecules broken apart during the day by solar ultraviolet radiation. And finally, just under Canadarm's elbow, is a streak of green--the aurora borealis. There was no big geomagnetic storm underway when the picture was taken. Nevertheless, the Northern Lights were there.
Breathtaking... x 1000.