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Spacewatch
Spacewatch: Beginning in 1984, and initially under the leadership of Tom Gehrels, 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 1923, this telescope was moved to Kitt Peak, Arizona in 1963. In 1983, this instrument was donated to the Spacewatch team and in 1984 it then became the first telescope to detect and discover asteroids and comets with electronic detectors (CCDs, as opposed to photographic plates or film).

The initial 320 x 512 RCA CCD detector used from 1984 to 1988 was replaced with a large format 2048 x 2048 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 23 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 ("drift-scan") while the CCD detector was constantly read out, this telescope scanned 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.

This system was the first to discover NEOs with CCDs, the first to discover comet with a CCD, and the first to discover an NEO with automated image processing software.

In 2001, the Spacewatch group began observing with a newly built 1.8-meter aperture telescope designed for follow-up of asteroids that get fainter after discovery. In late 2002, a large-mosaic CCD camera (four 4608 x 2048 CCDs) was added to the 0.9 meter, and the optical system was replaced to allow a wider field-of-view (2.9 square degrees). The 0.9-meter design now operates in the "stare" mode rather than in the previous "drift-scan" mode, whereas the 1.8-meter telescope continued to be operated in the "drift-scan" mode until 2011. From 2005 through 2008 the Spacewatch group gradually shifted their emphasis from NEO discoveries to follow-up observations that are critical for securing accurate orbits. In 2011 October the imaging detector on the 1.8-meter telescope was replaced with a "staring" CCD with finer pixel resolution, fast readout, and flatter focus. With it, 54% more observations of NEOs are being made, with astrometric residuals half the size as before.

The Spacewatch Principal Investigator is Robert S. McMillan For more information, see: http://spacewatch.lpl.arizona.edu/

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