Occultation Timing:
Determining Asteroid Size & Shape

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A stellar occultation occurs when the light from a star is blocked by an intervening body (such as a planet, moon, or asteroid) from reaching an observer. Amateur astronomers have been using occultation timing to measure the size and shape of asteroids with high accuracy for many years. Until about 5 years ago, observations were limited by the ability to predict these events with enough certainty to reward participants with high probability of success. The Global Astrometric Interferometer for Astrophysics (GAIA) is a European Space Agency astronomical observatory mission. Its goal is to create the largest, most precise three-dimensional map of the Milky Way. Improvements in our knowledge of both star positions and asteroid orbits, driven by data from the GAIA mission, have allowed many more positive measurements to be made. Steve Conard describes how we use modest sized telescopes and relatively inexpensive cameras to collect occultation data, along with open source software tools to predict events and analyze the resulting data.

Steve Conard has been a member of the International Occultation Timing Association (IOTA) for 15 years and was recruited by Dr. David Dunham – famous for his work in celestial mechanics – when they both were working at Johns Hopkins Applied Physics Laboratory. He has participated in two NASA sponsored trips to Argentina to collect data on the Kuiper belt object, Arrokoth, that was used to plan the New Horizon flyby. He regularly uses his Bobcat Observatory in Wellsboro, Pennsylvania to collect occultation data.

Steve has been an amateur astronomer for more than 50 years. His love of telescope making as a teenager turned into a 40 year career working for the Johns Hopkins University developing optical systems as an optical engineer. Most of his career was spent working on NASA astrophysics and planetary missions. This includes being in the role of lead engineer for the LORRI camera on the New Horizons mission to Pluto for the past 20 years.

Partially retired and now living in Wellsboro, Steve recently founded the Pennsylvania Wilds Astronomy Club. He regularly volunteers at several Pennsylvania State Parks and is working to control light pollution in the Wilds by working with several advocacy groups. His other interests include hiking, railtrail biking, and his antique motorcycle.


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