Identifying space debris in the night sky

Before we look at these objects in more detail, it may be useful to describe the appearance of comets, asteroids and meteorites in the night sky, so that the visual difference is clearly understood and the observer will be in no doubt as to what they have seen!

Comets appear in our skies from time to time. They vary considerably in their brightness or magnitude. In fact, at any one time there are almost certainly several comets visible to astronomers with large telescopes, but more rarely are there comets visible to the naked eye. Briefly, a comet may appear as little more than a faint "fuzzy star" in the sky, difficult to identify if you aren't familiar with the constellations; or, in the most spectacular cases, the comet may be very obvious, with a bright head or coma and a long tail trailing away. In all cases, the comet moves very slowly, and several hours must pass before any significant movement can be noticed against the background of stars.

If, on the other hand, you look up into the night sky and see a brief streak of light, then you have witnessed a meteor. Once more these objects vary in brightness, from those far too faint to be seen with the naked eye, to the bright fireballs which occur very occasionally, and can be so bright that they cast shadows. At certain times of the year, many more meteors than normal can be seen, and these events are called meteor showers.

Asteroids are more difficult to observe than either of the first two objects discussed, and are particularly hard to identify unless you have a pair of binoculars or a telescope, a dark sky, and know exactly where to look. The easiest way of spotting an asteroid is usually using photography, identifying any stars on the frame which appear to "move".

Now that we've explained a little about what you'll see in the night sky when you look at a comet, asteroid or meteor, we can investigate these bodies in more detail.