Great comet

[2] The vast majority of comets are never bright enough to be seen by the naked eye, and generally pass through the inner Solar System unseen by anyone except astronomers.

When they approach the Sun, large amounts of gas and dust are ejected by cometary nuclei, due to solar heating.

All these temporarily made comet 17P the largest (by radius) object in the Solar System although its nucleus is estimated to be only about 3.4 km in diameter.

However, comets behave differently, due to their ejection of large amounts of volatile gas which then also reflect sunlight and may also fluoresce.

Halley's Comet, for example, is usually very bright when it passes through the inner Solar System every seventy-six years, but during its 1986 apparition, its closest approach to Earth was almost the most distant possible.

On the other hand, the intrinsically small and faint Comet Hyakutake (C/1996 B2) appeared very bright and spectacular due to its very close approach to Earth at its nearest during March 1996.

Its passage near the Earth was one of the closest cometary approaches on record with a distance of 0.1 AU (15 million km; 39 LD).