What is a Comet Tail?
Every active comet has a tail — that’s part of what makes a comet a comet. Where does a comet’s tail come from? For most of their lifetimes, comets are ice-cold objects on the fringes of the solar system, and lack tails. They are space rocks primarily made up of ice and dust — when a comet is active, this rock is called the nucleus. As the comet orbits the Sun, it eventually passes into the inner solar system, where the solar wind and sunlight becomes intense enough to start vaporizing some of the comet’s ice and dust, which subsequently ionizes and becomes the long, stretched-out comet tail. A comet tail can become extremely long — one astronomical unit (Earth-Sun distance, 150 million km or 93 million mi) — the coma, or immediate atmosphere around the comet, can be larger than the Sun. All this from a nucleus anywhere between 100 meters (328 ft) and 50 km (31 mi) across, with a 10 km (6 mi) diameter being typical for comets visible to the naked eye. Because comets only spend a sm
