https://www.wired.com/story/how-two-nobel-laureates-spotted-the-first-exoplanet/

The 2019 Nobel Prize for Physics was awarded yesterday in part to Michel Mayor and Didier Queloz for an amazing discovery they made back in 1995: the first detection of a planet orbiting a far-away star similar to our sun. Before that, the only planets on the map were the eight in our own solar system. We didn’t even know if planets were common or rare in the universe—a question with big implications for the possible existence of alien life.

It was quite a feat of scientific sleuthing. Mayor and Queloz looked at a star in the Pegasus constellation called 51 Pegasi, which is 50.45 light years away. We can see the light given off by the star, but at that distance the angular size of the source is too small for telescopes to resolve. In other words, we can’t really see the star itself. And if you can’t see the star, you certainly can’t see a much smaller planet circling it.