Exoplanets
All of the planets in our solar system orbit around the Sun.
Planets that orbit around other stars are called exoplanets.
They are very hard to see directly with telescopes as they are relatively small and very far away.
In addition, exoplanets are hidden by the bright glare of the stars they orbit.
Astronomers have to use other ways to detect and study these distant planets.
One way to search for exoplanets is to look for 鈥渨obbly鈥 stars.
A large planet orbiting a star causes the star to orbit off-centre.
It is pulled to the side by gravity between the star and the planet.
From a long way away, this makes the star look like it is wobbling.
Only large planets can be detected this way but already hundreds of exoplanets have been discovered using this method.
To detect smaller, earth-like, exoplanets, a second method is used.
Astronomers look for the drop in the brightness of a star as an exoplanet, orbiting the star, passes between it and the Earth.
This is called the transit method.
As the exoplanet transits the face of the star, it blocks out some of the light reaching Earth.
The dip in brightness is evidence for the exoplanet.
The first confirmed detection of an exoplanet occurred in 1992.
As of 1 December 2018, there are 3,903 confirmed exoplanets.