In the 16th century everyone knew that Earth was the center of the cosmos. But this made it impossible to predict the motions of heavenly bodies, even if they moved in elaborate circles within circles. Copernicus turned the idea on its head and put the Sun at the center. A revolution had begun!

Astronomy Day has been an annual celebration of astronomy for nearly forty years of "bringing astronomy to the people." See if you can find an event near you. If not, create your own event by skywatching with a friend - our Absolute Beginners guides will help you out.

On April 12, 1961 Yuri Gagarin saw what no human had ever seen before: the Earth from space. Now "First Orbit" allows you to imagine that you are making the historic voyage. Film shot from the International Space Station creates the views, but you'll also have Philip Sheppard's music.

Leo is a Zodiac constellation and its stars have represented a lion for over four thousand years. Leo contains one of the brightest stars in the sky and one of the dimmest, as well as a selection of spiral galaxies loved by amateur astronomers. And what was Regulus's dark secret?

Saturn is golden in the sky, and a telescope shows a ring system to take your breath away. If you could find enough water Saturn would float, and its moons are amazing. But if you don't like freezing weather, 1000-mph winds and lightning storms the size of continental USA, don't plan any visits.

What would it be like to leave Earth's protective embrace and journey to an alien world? Only twenty-four men have ever experienced this - Apollo astronauts. "In the Shadow of the Moon" uses original footage & astronaut interviews to tell the story of one of the defining events of human history.

Days lengthen, flowers blossom and it's starting to get warmer. Even if your spring weather is late, daffodil-colored star Arcturus says it's spring. Use the Big Dipper to find Arcturus, Polaris the pole star, the constellation of Leo the lion, and a number of galaxies and nebulae.

Mars has no little green men, but it's a fascinating place. It has a mountain three times the height of Everest and a deep valley that dwarfs the Grand Canyon. Although Mars has no liquid water on the surface, if the southern polar icecap melted, it could cover the planet 36 feet deep in water.

Nebulae are titanic clouds of gas and dust - celestial gossamer in the spaces between the stars. They're stellar nurseries, stellar graveyards and dark constellations. Some of their mysteries have been penetrated by infrared telescopes, but the cloaking dust still keeps some secrets.

Caroline Herschel was an intelligent young woman trapped in domestic servitude by her mother. Her brother William rescued her and trained her as a singer. After he discovered the planet Uranus, the two of them ended up forming a great partnership whose work revolutionized the study of astronomy.