Mass has gravity, and gravity is a very social thing. Two bits of mass spy each other across the room (or the universe) and try to get closer. If they get close enough, they end up in an orbit around each other, possibly in a spiral until they collapse together, though this doesn't always happen if the escape velocity is sufficient to keep them from falling into each other. (That's what most orbits are: falling, but failing to hit the ground.)
The centre of gravity about which these object spiral about is called the barycenter.
Looks like this:
|Do-si-do. The barycenter is the red cross in the middle.|
|Pluto and Charon and their barycenter, the cross in the middle.|
When one object is distinctly more massive than the other, the barycenter will be located within the larger object, such as the Earth and the Moon:
This gives the Earth a little bit of a wobble, instead of a full-on do-si-do.
We noticed our Sun has a bit of a wobble, due to the gravitational influence of the planets about it. In fact, the Sun's wobbled quite a bit:
|Notice how sometimes the barycenter's inside the sun and sometimes its not?|
Yeah, not surprising, considering what we know about gravity. Then some clever soul thought, if our Sun wobbles due to planets pulling on it, wouldn't other stars wobble for the same reason?
Whoa! Mind blown! So we started looking at nearby stars with this Wobble Method (also called Radial Velocity or Doppler Spectroscopy Methods) to see if they had a wobble.
Ohmigosh, they did! Thus, we discovered exoplanets. And we said, "That's so cool!!!" (Then we felt slightly stupid because we hadn't figured something so simple out until now.)
Gamma Cephei Ab was the first exoplanet detected in 1989 (confirmed in 2002), and since then, we've uncovered evidence for thousands of exoplanets.
Nice to know we're not alone.
Now, there's lots of other methods for detecting exoplanets, but it all started with noticing how gravity made things wobble.
Wobbling isn't just for detecting exoplanets. Lots of other discoveries are due to the observation of wobbliness. Go hardcore and check out wobbliness from asteroids with moons to entire galaxy clusters. Even browsing through the list of titles is fascinating. Never be afraid to read an abstract. Save your freaking out for the paper itself.
Her Grace believes that love makes the world go round, but gravity rules the universe.