Occultation by the Asteroid Dido - June 6, 2006


This occultation of 2UCAC 17361090 (mag= ) was pretty much a "sure thing" as far as the rank and path. We were dead center and the path predicted uncertainty was very low. But the star was faint and the altitude low. Karl carefully figured out where the occultation would be visible from his property, as this was comfortably above any fog. My plan was to come up for a visit the night before, then sleep there and get up in the early morning for the occultation.

We had challenges... didn't get the VTI working, with heavy tree cover and no satellite synch; I forgot the f/3.3 and couldn't locate and focus the star quickly enough on the screen. So pulled and went visual at the last minute. I lost the star probably because it disappeared; probability of an occultation at my location was 85% according to the predictions. Star only visible with averted vision, and it's visibility noticeably deteriorated during the 3 minutes or so of concentrated observing. "R" appeared definite and quick reaction time, perhaps because diffraction made it momentarily brighter. However, my first impression of the location of the "R" was a tad (less than 1 arcmin) north of the expected position, but this is uncertain as the tiny cresent of stars marking the reference was itself getting pretty hard to see in the lowering altitude and rising dawn. Derek Breit had an 8 sec occultation from well north of me, consistent with a slight south shift, and suggesting that I indeed should've gotten the full 16 second occultation predicted. His "R" was at 11:39:35.0, so adding 2.0 seconds for the delta in midtimes for our locations, and 4 seconds to account for my being on the centerline, gives a predicted "R" time for me of 11:39:41.0, so this seems consistent with my "R" being real. My IOTA report is here.