Hubble Space Telescope
  • noun a telescope mounted on a satellite orbiting earth, launched in 1990.
  • One of the most successful instruments in the history of science, the HST was placed into orbit in 1990 after many years of planning and delay, especially caused by the 1986 Challenger space shuttle disaster. The 12 tonne spacecraft has a telescope with a 2.4m main mirror, which by being placed above the Earth’s atmosphere can be used to see objects as faint as the 31st magnitude. After launch the telescope, a joint project between NASA and ESA, has been serviced by visiting astronauts whose missions have included replacing its solar arrays, which were causing the spacecraft to shake as they expanded and contracted upon entering and leaving sunlight, and supplemented its optics to compensate for a slight miscalculation in the shape of its main mirror surface. The HST’s instruments include faint-object and wide-field cameras and photometers and spectrographs. It is used mainly to examine objects in deep space, including distant galaxies and parts of our own galaxy where activities such as star formation are going on, but has also produced startling images of solar system objects such as Mars, and Jupiter during the 1994 impact of comet Shoemaker Levy 9. The determination of the distance scale of the universe – in other words of the Hubble Constant – is, appropriately, its most significant mission. It is likely to last 15–20 years in orbit.

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