Skylab was an American manned space station which flew between 1973 and 1977. There were three crews who stayed on board Skylab, and they remained on the station for 28, 59 and 84 days, respectively. The picture shows Skylab as photographed by the third crew as they prepared to dock with the station.

The bit that you can see with the four solar panels shaped as a cross was called the Apollo Telescope Mount (or ATM for short), and contained several instruments that studied the Sun. Data from the ATM is still used today, over 20 years later!

Image courtesy of NASA.