A block of ice and dust a few kilometres across which, as it nears the Sun, grows a coma and tails. The curved, yellowish dust tail and the straight, bluish gas tail point away from the Sun. Their brightness is hard to predict.
Related terms
- Meteor shower
When the Earth passes through the dust trail left by a comet, meteors multiply for a few nights. The Perseids peak around 12 August and the Geminids around 14 December, with up to 100 to 150 meteors an hour in ideal conditions. Watch them with the naked eye, lying down, away from lights.
- Asteroid
A small rocky body orbiting the Sun, most of them between Mars and Jupiter. In a telescope it looks like a star, but you can see it move from one night to the next. Vesta can reach magnitude 5.3 and become barely visible to the naked eye under a very dark sky.
- Messier catalogue
The list of 110 deep-sky objects, M1 to M110, that the comet hunter Charles Messier published from 1774 so as not to mistake them for comets (the last entries were added later). It gathers the finest clusters, nebulae and galaxies visible from mid-northern latitudes. It is the ideal observing programme for beginners.
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