The Hubble Space Telescope (HST) was launched from on-board the Space Shuttle Discovery on April 24, 1990. This photograph was taken by a Discovery astronaut shortly after the telescope had been released into a circular orbit 610 kilometers (380 miles) above the Earth. The solar arrays, which collect solar energy to power the telescope, have been unfurled. These are the paddle-like objects on either side of the telescope tube. The high-gain antennas, used to communicate with the ground, have also been extended. But the door over the end of the telescope tube is still closed to protect the delicate mirrors and instruments from contamination. The shiny door reflects clouds in Earth's atmosphere far below.
The HST was named in honor of the American astronomer Edwin P. Hubble (1889-1953), who discovered that the universe is expanding. Its main mirror is 2.4 meters (94 inches) across. When first launched in 1990 it was equipped with five instruments: two cameras for taking direct pictures, two spectrographs for analyzing light, and a high-speed photometer for measuring the brightness of stars and galaxies. The Fine Guidance Sensors, used for pointing the telescope very accurately, can also be used to measure the positions of celestial objects.
