New Optical Search:
Different Telescope,
Same Small Comets
Part 3

The primary purpose of this search was to confirm the results of a previous optical search for the small comets more than a decade ago. The first optical detections of the small comets were acquired with the Spacewatch Telescope at Kitt Peak in Arizona in 1989. This search, conducted by Jet Propulsion Laboratory physicist Clayne Yeates, yielded positive results. Taking into account the fact that the primary mirror of the IRO is significantly smaller than the primary mirror of the Spacewatch Telescope used in the 1989 search, the average number densities of small comets detected with the IRO are similar to that observed previously by the Spacewatch search within a factor or two or three.

The small comets are small, dark objects which are moving in a prograde streams with speeds of 10 km/s near the Earth. A telescope with field of view staring in fixed directions on the celestial sphere, which is the usual mode of observing, is not able to record the presence of the small comets because of their rapid apparent motion across the image. Thus it is necessary to move the telescope's field of view so that the image of the small comet dwells at nearly the same location in the telescope's detector array. This "skeet shooting" mode of observing the small comets was devised by the late Clayne Yeates for the 1989 Spacewatch Telescope search. The closer the small comet is to the telescope, the brighter it is, as long as it is outside of the Earth's shadow where the small comet is illuminated by the Sun. With the IRO the small comets are observed at a distance of about 30,000 miles, with one series of observations at 55,000 miles.

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