Question: how can you tell if there a planet or a star?

Hugh Osborn answered on 21 Nov 2014:

Stars, like our sun, are pretty bright things! Anything that glows bright enough to be detected by our telescopes is likely a star.

Planets are a lot more difficult – they are incredibly small, very close to their stars and dont give off their own light. So we cant see them directly by looking through a telescopes. Instead, we find them indirectly. For example, the planet, even though it is much less heavy, has a gravitational effect on it’s star and we can detect the slightest tug from the planet in the starlight (specifically it’s colours, which get shifted due to the stars motion).

In a few cases, the planet passes in front of it’s star, blocking some of it’s light (a bit like how the moon eclipses the sun once in a while). We can spot this from Earth as repeated dimmings in the starlight, and can work out how big the planet is. This is the way I find planets, and our group have discovered more than 120 new planets this way.