The Hubble Space Telescope (HST) is a space-based telescope that was launched in 1990 by the space shuttle.

From its position 380 miles above the Earth’s surface, the HST has expanded our understanding of star birth, star death, and galaxy evolution, and has helped move black holes from theory to fact.

In its first 15 years, the telescope recorded over 700,000 images.
 

Photo:  The Hubble Space Telescope floats against the background of Earth, 2002.

The telescope’s instruments are the astronomer’s eyes to the universe. Its instruments include the

• Wide Field Planetary Camera 2 (WFPC2),
• Near Infrared Camera and Multi-Object Spectrometer (NICMOS),
• Advanced Camera for Surveys (ACS), and
• Fine Guidance Sensors (FGS).

When first launched, the HST’s primary mirror was out of shape on the edges by 1/50 of a human hair. This very small defect made it difficult to focus faint objects being viewed by the Hubble. Because the HST is in low Earth orbit, it could be serviced by a shuttle. The defect was corrected in one such servicing mission.  ^[2]

Hubble Space Telescope's  current complement of science instruments include three cameras, one spectrograph (not functional at this time), and fine guidance sensors (primarily used for accurate pointing, but also for astrometric observations).

Because of HST's location above the Earth's atmosphere, these science instruments can produce high-resolution images of astronomical objects. Ground-based telescopes are limited in their resolution by the Earth’s atmosphere, which causes a variable distortion in the images.

Hubble can observe ultraviolet radiation, which is blocked by the atmosphere and therefore unavailable to ground-based telescopes. In the infrared portion of the spectrum, the Earth’s atmosphere adds a great deal of background, which is absent in Hubble observations. 

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