2 (b.c.) Comets
One of the most glorious things you can see in the night sky is a comet. But what exactly is a comet? You can think of a comet as a “dirty snowball” about the size of a mountain. Comets are loose collections of ice, dust, and small rocky particles whose orbits are usually very long, narrow ellipses.
As a comet approaches the sun and heats up, some of its gas and dust stream outward, forming a tail. The name comet means “long-haired star” in Greek. Most comets have two tails—a gas tail and a dust tail. Both tails usually point away from the sun.
A comet’s tail can be more than 100 million kilometers long and stretch across most of the sky. The material is stretched out very thinly, however, so there is little mass in a comet’s tail.
As a comet approaches the sun and heats up, some of its gas and dust stream outward, forming a tail. The name comet means “long-haired star” in Greek. Most comets have two tails—a gas tail and a dust tail. Both tails usually point away from the sun.
A comet’s tail can be more than 100 million kilometers long and stretch across most of the sky. The material is stretched out very thinly, however, so there is little mass in a comet’s tail.