Fourth of seven documentaries that will bring you the magic of music and a motor-car capable of a mile in six seconds.
But tonight: Spy in the Sky
Every hour of every day dozens of spy-in-the-sky satellites are peering down at us from space.
What are they looking for and what can they see?
Apart from the weather satellites, other spacecraft are busy sending back spectacular pictures of the earth's surface, particularly for oil and mining companies. But the real super spies are the military satellites used by Russia and the USA. What they can see of each other from space is top secret, but there's enough evidence to show they can see an awful lot more than you think.