The Hubble telescope, named for famous U.S. astronomer Edwin Hubble, was in development by NASA for years before it finally entered space on the Discovery space shuttle in 1990 [source: NASA]. For more than 20 years, it has allowed scientists to learn detailed information about the stars, black holes and more abstract mysteries, like the age of the universe.
The Hubble is a Cassegrain reflector telescope. This means that the Hubble has a long tube to let in light, plus various mirrors and lenses for focusing and magnifying the images. Light enters a hole and bounces off a primary mirror and onto a secondary mirror; the secondary mirror then reflects the light back through a hole in the primary mirror to a focal point behind it. The focal point contains three smaller, half-reflective and half-transparent mirrors that relay the light to various instruments [source: NASA].
The Hubble telescope has some special scientific instruments that allow it to view all the different wavelengths on the light spectrum. Some of the most important instruments are the Wide Field and Planetary Camera 2 (WFPC2), which is the telescope's main "eye;" the Space Telescope Imaging Spectrograph (STIS), which acts like a prism to separate incoming colors of light and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), which allows the telescope to see infrared light [source: NASA].
The NICMOS is actually made up of three highly sensitive cameras that can see infrared light and thus detect heat. If the Hubble is trying to track an object obscured by interstellar gas and dust, NICMOS can detect the object's heat and form an image. In 2002, the Advanced Camera for Surveys was added to the Hubble telescope, doubling its field of view and allowing astronomers to study some of the universe's earliest activity [source Hubble]. NASA plans a replacement for the Hubble, the James Webb Space Telescope, though the new telescope won't be ready to launch until about 2018 [source: Baer].
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