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MKO Provides Measurements of Comet's Position

Astrometry is the branch of astronomy that is concerned with measurements of the celestial bodies, especially those made to determine their positions and movements.

Measuring the precise position of an asymmetrical object at a distance of 83 million miles away is not an easy task. The Deep Impact Navigation Team at the Jet Propulsion Laboratory (JPL) in Pasadena needed accurate data on the position of Comet Tempel 1, and Mauna Kea Observatories (MKO) and IfA personnel played a key role in this.

A total of 5171 position measurements were made of Comet Tempel 1 since 1994, according to Steven Chesley, who did the orbit calculations for the mission at JPL. MKO provided 374 of these measurements. Of the total observations, only 951 were of high enough quality to be used in these calculations, including nearly all of the MKO data, so Mauna Kea provided 40 percent of the astrometry for the final orbit calculation. During the active phase of the comet, Mauna Kea data comprised 74 of the 671 observations, or about 11 percent.

IfA astronomer Karen Meech made most of the Mauna Kea observations, and graduate student Nick Moskovitz did most of the astrometric measurements on them, with some help from postdoctoral researcher Jana Pittichová. IfA astronomers Yanga Fernández and David Tholen also contributed some of the observations and astrometric measurements, respectively, in the final days before impact.

The time of the impact was only 10 seconds early, well under JPL's 17-second uncertainty estimate.