Asteroid 2000 RD 53 can be seen streaking from left to right in this sequence of images. The three images were taken about 2 minutes apart. Photo: Spacewatch

University of Arizona Spacewatch Project founders just realized a 20-year dream.

Spacewatch astronomers led by Tom Gehrels and Robert McMillan have used a 36-inch (0.9-meter) UA telescope on Kitt Peak to electronically scan the skies for asteroids throughout the solar system since 1984. Before Spacewatch, astronomers used photographic plates to hunt asteroids.

Spacewatch has been a striking technological and scientific success. But Gehrels' and McMillan's original hope in 1980 was to use a 72-inch (1.8-meter) telescope in their electronic asteroid survey.

A couple of weeks ago, perseverance and hard work paid off. The new 72-inch Spacewatch telescope captured its first light from an asteroid, asteroid 2000 RD 53, on Sept. 14. The Spacewatch team took first digital data with the telescope on the same very fast moving near-Earth object on Sept. 19.

Then on Sept. 28, the Spacewatch team made its most interesting observations yet. Telescope-drive software tracked the fast-moving asteroid 2000 SM10 for more than three hours.

"I think the 1.8-meter will be the biggest telescope in the world dedicated full time to asteroid discovery and astrometry," McMillan, Spacewatch director, said. (Astrometry is a branch of astronomy that measures the positions and movements of celestial bodies.)

Astronomers refer to brightness in terms of "magnitude," with larger magnitudes corresponding to brighter objects. The unaided human eye when dark-adapted under clear, dark sky sees objects at about six-and-half magnitude brightness. The 36-inch telescope detects objects down to 21.7 magnitude. (That's roughly equivalent to photographic film rated at ASA one million, McMillan noted.)

The 72-inch will detect objects down to 22.7 magnitude, or two-and-a-half times fainter than the 36-inch can detect. The bigger telescope will discover twice as many asteroids as the smaller telescope now finds, McMillan said.

The 1.8-m Spacewatch telescope in its upright position. Photo: Alain Maury

Plans are to upgrade - not retire - the 36-inch telescope, McMillan said. Now that the 72-inch telescope is coming on line, the 36-inch can be temporarily shut down late next year so new detectors can be installed. The new detectors are 10 times larger than the detector that has been used in the telescope since 1989. "That upgrade alone will boost our discovery rate by a factor of 6 to 10, depending on how we use it."

"The telescopes will be complementary. The smaller telescope, when upgraded, will get a much wider field of view, or cover 10 times as much sky. The 1.8-meter will concentrate on finding the very faint objects," McMillan said. Faint targets for the new telescope include the small Near-Earth Asteroids, some of the bigger and brighter Trans-Neptunian Objects in the Kuiper Belt, and Near-Earth Asteroids that have previously flown by Earth as these objects usually appear fainter on successive swings by the planet, he added.

The 72-inch telescope looks radically different from its white, single-barreled 36-inch elder sibling. UA originally acquired the 72-inch, f/2.7 fused silica mirror blank from the military for an asteroid telescope, but the mirror blank was loaned to the Multiple-Mirror Telescope on Mount Hopkins, Ariz., until 1993, Gehrels noted. The mirror is mounted in altitude-azimuth type mount in a mirror-support cell contributed by the UA/Smithsonian MMT Observatory. The telescope itself was built at the UA's University Research Instrumentation Center. Telescope designers used "folded prime focus" rather than a straight prime-focus for a more compact telescope that could be housed in a smaller, less expensive dome. The telescope support structure is painted black to reduce light scattering, prompting engineers and astronomers to dub it the "Stealth" telescope. Contributions from foundations, corporations and private individual donors, and grants from NASA and the U.S. Air Force Office of Scientific Research paid for the $5 million telescope. The venerable 36-inch Spacewatch telescope, which was originally sited on the UA campus in 1921, moved to Kitt Peak in 1962. Among its distinguished accomplishments:

• First to use CCD scanning routinely in astronomy
• First to use CCDs to survey the sky for comets and asteroids
• First near-Earth asteroid detected with a CCD (1989 UP)
• First astronomical group to develop automated, real-time software for moving-object detection
• First to discover a near-Earth asteroid by software (1990 SS)
• First automatic discovery of a comet (C/1992 J 1)
• Detected smallest known asteroid (1993 KA2, about 4 - 9meters diameter)
• Detected closest known approach of an asteroid to the Earth (1994 XM1, at 105,000 km)
• Identified two new asteroid populations - small near-Earth asteroids and distant Centaurs (objects in unstable orbits between Jupiter and Neptune)
• Discovered fastest rotating and most accessible asteroid at time of discovery (1998 KY 26)
• Continues to detect 20 to 30 near-Earth asteroids annually
• Smallest telescope in the world for Trans-Neptunian Object discoveries. (Trans-Neptunian Objects, or TNOs, are primordial objects orbiting the sun beyond Neptune.)