Comets are often referred to as "dirty snowballs" because they contain a mixture of ice and dust. When they approach the Sun, the heat from the star can cause the ice to sublime, or turn into gas, creating a glowing coma, or head, and tail.
Comet Borisov is expected to make its closest approach to the Sun on December 7. At that point it is expected to be roughly 186 million miles (300 million kilometers) distant.
The comet is expected to brighten during early December and may become visible to the naked eye by mid-December.
