Astronomy Picture of the Day

Explanation: Launched thirty years ago, NASA's Voyager 1 and 2 spacecraft are now respectively 15 billion and 12.5 billion kilometres from the Sun, equivalent to about 14 and 11.5 light-hours distant. Still functioning, the Voyagers are being tracked and commanded through the Deep Space Network. Having traveled beyond the outer planets, they are only the third and fourth spacecraft from planet Earth to escape toward interstellar space, following in the footsteps of Pioneer 10 and 11. A 12-inch gold plated copper disk (a phonograph record) containing recorded sounds and images representing human cultures and life on Earth, is affixed to each Voyager - a message in a bottle cast into the cosmic sea. The recorded material was selected by a committee chaired by astronomer Carl Sagan. Simple diagrams on the cover symbolically represent the spacecraft's origin and give instructions for playing the disk. The exotic construction of the disks should provide them with a long lifetime as they coast through interstellar space.