Years ago, if you weren't serious about being an astronomer, a good career-killer would have been hunting for exoplanets. It's different now. Stuart Clark tells the story from the first discovery of a planet orbiting another star to the current Search for Earth's Twin.

Mimas is named for a giant in Greek mythology, but Saturn's moon is no giant. It's less than 400 km (245 mi) across and the smallest body we know of that's rounded by gravity. The moon also has a bizarre resemblance to the Death Star in George Lukas's Star Wars films.

If you look at your calendar to find today's date, you can see the month, days of the week and maybe some appointments. But you're also looking at something that tracks Earth's journey around the Sun, reflects three thousand years of history and helps to hold our society together.

Earth's moon is “the Moon” because it was the only one humans had ever seen until 1610. That's when Galileo discovered moons orbiting Jupiter. By 1876 astronomers had found moons around all of the outer planets. So why did it take until 1877 for someone to find the moons of our neighbor Mars?

Imagine yourself under a dark autumn or winter northern hemisphere sky. You're looking towards the “W” of Cassiopeia, and notice a hazy patch between Cassiopeia and the constellation Andromeda. That is the Andromeda Galaxy (M31). Here are some fascinating facts about this stunning object.

We're used to having just one Sun, so the planet Tatooine in George Lucas's Star Wars was exotic with its double sun. Yet at least half the stars we can see in the sky are doubles. But a "double star" can be a true binary or just an optical double, which is a chance alignment of unrelated stars.