Tracking the rotation speed of solid planets, like the Earth and Mars, is a relatively simple task: Just measure the time it takes for a surface feature to roll into view again. But giant gas planets ...

Using new data from NASA’s Cassini spacecraft, researchers believe they have solved a longstanding mystery of solar system science: the length of a day on Saturn. It’s 10 hours, 33 minutes and 38 ...

Figuring out the day length of Earth is more complicated than you might imagine. While on average a day is 24 hours long, throughout the year the planet's rotation can speed up and slow down, with one ...