Because the Earth is doing the work of increasing the Moon's momentum, the Earth's rotation slows down in turn, as its momentum goes to the Moon. To put it another way, as the Moon's orbital momentum ...

All planetary systems have this point, called a barycenter, where their mass is perfectly balanced. For some systems - like Pluto and its moon, Charon - the barycenter is outside the planet. See more ...

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to ...

The moon has been Earth's close companion for billions of years, and while our view of its shape and size varies somewhat as it orbits our planet, it remains a constant presence in the sky. But could ...

NASA's Juno probe has flown closer to Jupiter and its largest moon, Ganymede, than any other spacecraft in more than two decades — and the images it beamed back of the gas giant and its icy orb are ...