Comets

Made of dust, ice, carbon dioxide, ammonia and methane, comets resemble
dirty snowballs. You may remember them as blurry smudges in the sky. Comets
orbit the Sun, but most are believed to inhabit in an area known as the Oort
Cloud, far beyond the orbit of Pluto. Occasionally a comet streaks through the
inner solar system; some do so regularly, some only once every few centuries.

Heads and tails

As a comet nears the Sun, its icy core boils off, forming a cloud of
dust and gas called a head, or coma. Comets become visible when sunlight reflects
off this cloud. As the comet gets closer to the sun, more gas is produced.

The gas and dust is pushed away by charged particles known as the
solar wind, forming two tails. Dust particles form a yellowish tail, and
ionized gas makes a bluish ion tail. A comet's tails, like these on comet
Halley, always points away from the Sun.

Meteor showers

When Earth crosses the path of a comet, even if the comet hasn't been
around for a few years, leftover dust and ice can create increased numbers of
meteors.

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