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You can find scientific and technical information on the telescope under
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DLR, in partnership with NASA on the SOFIA project,
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Home > About SOFIA > SOFIA Telescope


SOFIA Telescope
Click on image for enlarged view.

Like most modern research telescopes, the SOFIA telescope uses a mirror to concentrate and focus the incoming light. When it comes to large telescopes, mirror-based systems (called "reflectors") have proven to be much more practical than lens-based telescopes (called "refractors") because they are much easier and less expensive to build and use.

SOFIA’s primary mirror, located near the bottom of the telescope, is 2.7 meters (almost 9 feet) across. The front surface, which is highly polished and then coated with Aluminum to ensure maximum reflectivity, is deeply concave (dished inward). Incoming light rays bounce off the curved surface and are all deflected inward at the same time they are reflected back up toward the front of the telescope.

Before the light reaches the telescope’s front end, however, it is intercepted by a small secondary mirror (about .4 meters across), which sends the light back down toward the center of the main mirror. About a meter above the center of the main mirror, a third mirror sends the light out through the side of the telescope, down a long tube which projects through the main aircraft bulkhead into the interior of the SOFIA aircraft. There, at the telescope’s focal point, the light will be recorded and analyzed by one of several different instruments.
The SOFIA telescope's main support structure being tested in Augsburg Germany in October, 2001. Photo courtesy Man Technologie. Click on image for enlarged view.

Astronomers tend to compare telescopes based on the diameter of their primary mirrors. SOFIA’s telescope is usually referred to as a 2.5-meter meter telescope, rather than 2.7 meters, because the optical design requires that only about 90% of the mirror’s reflecting surface (called the "effective aperture") can be used at any one time. Although SOFIA’s telescope is by far the largest ever to be placed in an aircraft, compared to normal ground-based research observatories it is only medium-sized (the world’s largest single-mirror telescope, the Subaru, is 8.2 meters across).

International Cooperation

Under an international agreement between the United States and the German governments, the SOFIA telescope is being supplied by the German Aerospace Center (DLR). DLR is supplying the telescope and additional operation support in return for a portion of SOFIA's valuable observing time.

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Page Last Updated: February 19, 2004

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