And how do we know their sizes and distances?
In: Physics
If a planet passes in front of a star it causes the light from the star to bend slightly around it. This process is called lensing, and it makes the star look like it’s wobbling slightly every time the planet moves between it and us. By measuring how much the light bends you can work out how large the intervening object is. Distance is measured using parallax; how much the position of a star in the sky varies during the Earth’s orbit around our sun. The more a star seems to move, the nearer it is.
The size of stars is measured by looking at their brightness (how much light they emit) as well as their composition which we can find by analysing the different energy levels (called frequencies) in the emitted light. The relationship between all these things tell us what stage of life the star is in and how much stuff is in it, and hence how big it is.
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