More than 20 years ago astronomers picked out the first sign of a planet in another solar system. Over the next few years new discoveries trickled in, but soon new technology and new techniques turned that trickle into a torrent.
Where we once thought space was most an empty void, astronomers now reckon that it's just jammed with planets. There's already a list of 1,741 confirmed exoplanets, with thousands more waiting for confirmation. The current estimate is that the Milky Way galaxy—just one little galaxy!—is home to 17 billion Earth-like planets.
While understanding the intricacies of searching for exoplanets is quite difficult, the core concepts are surprisingly simple. In the video above, Minute Earth runs through the basics of some of the ways astronomers look for distant planets.
If you're after more detail, Smithsonian's Joseph Stromberg has a more in-depth explanation of some of these exoplanet-hunting techniques.