So, what’s an exoplanet? It’s just a planet that orbits a different star. Unfortunately, Planets are really small compared to stars and this makes them hard to find.

In our Solar System the smallest planet is Mercury which is only 0.3% the size of the Sun. Jupiter is the largest planet in the Solar System and it's 10% the radius of the Sun.

Earth is 0.9% the radius of the Sun

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Not only are planets small compared to stars, they’re also not as bright! Stars are fusing hydrogen into helium (and later more things that I won’t get into…) and the energy released from that is why they are so bright.

Planets are not fusing elements, so they’re not as bright. BUT they are warm, and warm things also emit light. Not at colors of light we can see with our eyes like stars do, but at longer wavelengths of light like the infrared (where #JWST will observe).

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So, #exoplanets are small and dim. Meaning until recently we couldn’t just take out a telescope and stare at a star and hope to see a planet around it. The light from the star would just overwhelm everything!

Back when people started thinking about actually finding planets there were two main suggestions: (1) look at how the planet’s gravity pulls on the star and (2) watch for the planet to cross in front of the star and block out a little bit of light

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We call the first method the Radial Velocity method.

You may think of an orbit as the planet orbiting the star, with the star stationary at the center. This is *almost* the truth, but even though planets are small compared to their stars they “tug” on the star ever so slightly causing it to move around.

This happens in our Solar System too! Jupiter is the biggest culprit - check out this gif (not to scale) of how Jupiter tugs on the Sun.

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@_astronoMay
I recall this!

Several planets in our own solar system were discovered this way, weren't they?