Asteroids: rocky travellers — Astronomy, 4–6 years
Asteroids are rocky pieces moving through space. Most travel around the Sun, and some are much smaller than a planet.
What an asteroid is
An asteroid is a lump of rock or metal travelling through space. It has no warm light of its own, and it can be as small as a pebble or much bigger than a house.
Why notice asteroids?
People study asteroids because they are ancient pieces left from the building of the solar system. Finding where they travel also helps us notice objects that could come close to Earth.
A simple asteroid count
Imagine three rocky objects in a picture: one is round, one is jagged, and one is tiny. Count only the objects with no light of their own: one, two, three. They could all be asteroids.
A common mix-up
It is easy to call every space rock a star because both can appear as bright dots in a picture. A star makes its own light, but an asteroid only reflects light from a star such as the Sun.
Asteroids outside school
Astronomers use cameras and computers to follow asteroids and predict their paths. Space missions have also visited some, taking close-up pictures and measuring what their surfaces are made of.
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