The Occultation by the Asteroid Pomona

Nov 18/19, 2015

Planning page

This was a good event - a v=11.0 star (10.0 in r band) occulted right as twilight was ending, 24 degrees above the horizon in Sagittarius. The predicted duration was only 2.2 seconds. The path for this event was right across Monterey Bay, with the predicted northern limit crossing San Andreas Rd south of Aptos. I had a busy day, teaching in the morning, returning by bike, and still groggy from a cough-syrup induced sleep late the night before. After getting back from Cabrillo at noon, and finishing up some financial decisions, I lay moribund until 3pm, then roused and got in a 2 mile run finished by shopping at the Farmer's Market downtown. Then shower, tossed the right stuff in the car, and hit the road. Traffic was brutal, and by the time I arrived at my office, printed the charts I prepared the night before, drove to the Observatory and packed up the 10" scope and gear, it was now only 50 minutes until the event. I'd not have time to get to my earlier plan of observing from Moss Landing, where odds were 38%, instead, with still bad traffic, I got off at San Andreas Rd with the intent of setting up in an open field I knew of just southeast of Manressa Beach. Skies were clear, just a little wispy cirrus which seemed to disappear at sunset. Temps in the 50's. I got set up quickly, 2-star aligned the 10", swapped in the Watec videocam with f/3.3 reducer, and found the target without any problem. I was ready to tape 11 minutes before the event. I tweeked the integration to 4x (2-frames) since the S/N looked good enough to get the additional time resolution. I snapped a few pix, watched as the predicted time of 2:09:09UT came and went, and no occultation. A miss. Oh well, not a great surprise. I packed up quickly and drove home, then one more short run to Bookshop Santa Cruz where I promised to meet students where we'd listen to cosmologist/particle physicist Lisa Randall give a talk.


The moon is just above the left corner of Capricorn, which is well outlined here. My target star is in the "teaspoon" formation of Sagittarius (teapot) to the lower right and off the frame

This is about 4 minute before the event

The target is below, the brighter tracking and comparison star is above.

The target star light curve is in blue, and clearly shows no occultation. The brighter comparison star is above. I let the tracking radii "drift" for each, since there was at most I knew only the possibility of the briefest of occultations. As it turns out, not even that. The time resolution is 1/16 sec.

Here's my IOTA report

My Coordinates from the IOTA VTI

Long=121 51.1390
Lat= 36 55.6522
Altitude=33.4 meters