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Spacewatch: Beginning in 1984, the 0.9-meter, Newtonian f/5 Steward
Observatory Spacewatch telescope has been used full time for surveying
comets and asteroids. First installed on the University of Arizona campus
in 1921, this telescope was moved to Kitt Peak, Arizona in 1962.
Subsequently, this instrument was donated to the Spacewatch team and
it then became the first telescope dedicated solely to the study of
planetary astronomy. The initial 320 x 512 RCA CCD detector was
replaced with a large format 2048x2048 CCD detector used during the
interval 1989-1992. This system had a field width of 38 arc minutes and
limiting magnitude of 20.5. The sensitivity of the CCD (quantum
efficiency) was doubled to 70% in 1992 when a thinned 2048 x 2048
CCD was installed and extended the limiting magnitude down to 21.0.
The 0.9-meter telescope is used about 20 nights per month to search for
near-Earth objects. By locking the right ascension axis in place and
allowing the star fields to drift through its field of view while the CCD
detector is constantly read out, this telescope scans at a rate that
covers about 200 square degrees of sky each month down to magnitude
21. Each region of sky is scanned three times, about thirty minutes apart,
to examine which objects have moved relative to the background stars.
Spacewatch has discovered many of the smaller near-Earth objects that
pass close to the Earth including a ten-meter sized asteroid (1994 XM1)
that has the record close Earth passage (105,000 km on Dec. 9, 1994).
In May 2001, the Spacewatch group discovered their first Potentially
Hazardous Asteroid (PHA) with a recently modified 1.8-meter aperture
telescope that has been designed to be a fast f/2.7 wide-angle instrument
suitable for more rapid monthly coverage of the skies for Near-Earth Object
discovery efforts.
In late 2002, a large-mosaic CCD camera (four 4608 x 2048 CCDs) was added to the 0.9 meter, and the optical
system has been modified to allow a wider field-of-view (2.9 square degrees). The new 0.9 meter design will operate in
a "stare" mode rather than in the previous scan mode.
In addition to the search for near-Earth objects and asteroid studies, the
Spacewatch team is involved with the study of the Centaur and
Trans-Neptunian minor planet populations and the sizes of short period
comet nuclei.
Robert S. McMillan: Principal Investigator
Robert Jedicke, Jeff Larsen, Joe Montani, and Jim Scotti: Research Specialists
Look here for additional information on the Spacewatch program:
http://pirlwww.lpl.arizona.edu/spacewatch/
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