On Jan. 26, the asteroid 693 Zerbinetta, a 40-mile wide rock that orbits the sun in a five year orbit, passed in front of a faint star in the constellation Auriga casting a thin shadow on the Earth that blocked the star from observers in the southwestern United States. As it happened, Sierra Vista fell close to the centerline of the predicted path of this occultation.

By precisely timing the blocking of the star at several points along the asteroid shadows path, scientists can build a map of the asteroid. With enough data points, the shape and size of the asteroid is revealed and knowledge of its rotation rate and orbit can be refined.

Members of IOTA, the International Occultation Timing Association, travel the world over filming and timing these occultations to build a database of asteroid measurements. They often enlist the help of other amateur astronomers along the predicted path of the event.

On the night of Jan. 25, members of the Huachuca Astronomy Club (HAC) were enlisted by IOTA member, Paul Maley of Carefree, Arizona, to record the passage of Zerbinetta in front of the faint star known by the catalog designation 2UCAC 46262076. The asteroid would block the star for only a few seconds, just minutes past midnight on the morning of Jan. 26. The measurement had to be perfect or the data would be useless.

The Patterson Observatory, on the campus of the University of Arizona Sierra Vista, was deemed to be just 1.98 miles from the centerline. HAC members David Roemer, Rick Burke and Ken Duncan manned the observatory and operated a video camera attached to an 8-inch telescope that rides piggyback on the observatorys 20-inch telescope. Special software was downloaded into the observatorys computer to insert a precise time stamp into the recorded video.

Mr. Maley set up similar equipment at my own observatory about eight miles east of Patterson and about three miles from the centerline.

Reducing the recorded video data to a graph of time versus brightness, a scientifically valuable data set is produced. Comparing that data from several sites along the path yields the desired information that can then add to our knowledge of this asteroid.

The Patterson Observatory is owned by the University South Foundation, Inc. and is operated by volunteers from the Huachuca Astronomy Club. This is not the first time that valuable science has been collected at the Patterson. It has been used previously to record an asteroid occultation, it is occasionally used to record asteroid observations for the Lunar and Planetary Laboratorys Target Asteroid Campaign and HAC astronomers used Patterson to participate in the worldwide Comet ISON observing campaign. Plans to participate in LPLs 4*P comet coma morphology study are ongoing as well. The observatory is open to the public once a month for a free open house observing session called Public Night.

The next Public Night is March 2. Doors open at 7 p.m.

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Local astronomers help map asteroid - Sierra Vista Herald