出典:Wiktionary
出典:Wikipedia
出典:『Wikipedia』 (2011/07/25 21:14 UTC 版)
A comet tail and coma are illuminated by the Sun and may become visible from Earth when a comet passes through the inner solar system, the dust reflecting sunlight directly and the gases glowing from ionisation. Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye.