HatNet is a project where a group of people work together to find new planets in space. They do this by using special telescopes that look up into the sky at night. Imagine you're lying on the ground and looking up. It's the same thing, but the telescopes are much bigger and they can see things that we can't see with just our eyes.
When the telescopes spot something strange in the sky, like a star that seems to be dimming or getting brighter, the scientists who run the project take a closer look. They study the light from the star to see if there is something passing in front of it.
If they see something, that could mean that there is a planet orbiting that star! The scientists keep watching the star to make sure it's really a planet, and they use fancy math to figure out how big the planet is, how hot it is, and what it could be made of.
This is important work because finding new planets helps us learn more about our universe and whether there might be other planets out there where life could exist. HatNet has helped discover hundreds of new planets so far, and the scientists are always looking for more.