Occultation

Occasionally an asteroid, in its orbit around the sun, passes in front of a background star, briefly blocking the light from that star. When that happens, there will be a spot on the surface of the earth the size and shape of the asteroid within which the star cannot be seen—it is “occulted”. ”. This “shadow” moves across the earth at a known speed, and along a path that can be predicted with reasonable accuracy. If this event can be observed and timed to sufficient accuracy, astronomers can use the data to refine the orbit of the asteroid, and, if seen by several observers, it should be possible to determine the asteroid’s size and shape.

The following photos show the results of our observation of the Marghanna event. There is a full-length, uninterrupted trail from a nearby star just above the image of the target star, TYC-2936-00356-1. The gap in the trail of our target star records the occultation.

The image at left shows (the upper start trail) the exposure with a star which is constant throughout the exposure. The lower star trail is broken- caused by the asteroid occultation.

The map below shows the path of the event shown on the previous page. This event on March 11, 2008 when 735 Marghanna, a 15^th magnitude asteroid, occulted a 9^th magnitude star, TYC 2936-00356-1.

The predicted path crossed out observatory in Pueblo, although we were on the very edge of the expected track. From our fixed location, we usually get one or two opportunities per month to make an observation. It seems, however, that more than half of those chances get clouded out. Combine this with the fat that most of the possible events are low probability due to a large uncertainty in the astrometry. This is one of the more successful recording that we have done but with a little bit of perseverance, that will change.

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