Comets are bright objects with long tails, which we sometimes see streaking across the night sky.
They may look spectacular, but a comet is just a dirty ball of ice a few kilometers across.
Many comets orbit the Sun, but their orbits are very long and they spend most of the time in the far reaches of the Solar System. We see them when their orbit brings them close to the Sun for a few weeks.
A comet’s tail is made as it nears the Sun and begins to melt. A vast plume of gas millions of kilometers across is blown out behind by the solar wind. The tail is what you see, shining as the sunlight catches it.
Comets called periodics appear at regular intervals.
Some comets reach speeds of two million km/h as they near the Sun.
Far away from the Sun, comets slow down to 1000 km/h or so – that is why they stay away for so long.
The visit of the comet Hale-Bopp in 1997 gave the brightest view of a comet since 1811, visible even from brightly lit cities.
The Shoemaker-Levy 9 comet smashed into Jupiter in July 1994, with the biggest crash ever witnessed.
The most famous comet of all is Halley’s comet.
Comet Kahoutek streaks through the night sky.
The tail of a comet always points away from the Sun.