Comet authority Fred Whipple has dubbed them “dirty snowballs”—small bodies of ice and dust only a few kilometers across. On close approach to the sun this frozen material vaporizes and streams away from the comet forming a tail millions of kilometers long. Charged particles emitted by the sun travel outward at hundreds of kilometers per second (the solar wind) causing the comet’s tail to act like a weather vane, always pointing away from the sun.
Comet Hyakutake and Polaris
Taken March 27, 1996 at Carlisle, Massachusetts
Nikon F3, 50mm, f/1.8, 2 min on Kodachrome 200