This event was originally one of the best of 2011 - an 8.5 magnitude star with high rank and large diameter predicted to pass straight over Cabrillo Observatory. However, weeks before the event, the diameter was listed by two different sources and the now instead of being 66 km across as determined by older IRAS satellite infrared data, it was listed as only 25 km across. Also, the path shifted north, now expected to cross the SF peninsula, with Cabrillo 68 km south of the centerline and south of the expected path. The rank was now in the mid 40's, and the odds of the event being visible from Cabrillo dropped to only 6%. It happened on a Monday night, November 8th, at 10:16pm. That was only a little over an hour after my 6-9pm Astro 3 class let out. So driving north to get into the predicted path wasn't an option. The star was bright and the event was important as it would shed light on the validity of the two different measures of the diameter. David Dunham flew out and joined Rick Baldridge from Foothill College. Also observing was Chris Kitting at his home near CSUEB in Hayward, only a hundred meters from the predicted centerline. Plus two stations from Walt Morgan, and Ted Swift in Davis, Derek Breit from home in Morgan Hill, among others.

The skies were clean, clear, cold, and damp from the recent rain. I brought Becky and Gene from Astro 9 and had them set up to do astrophotography projects and be there, so I could set up the 10" scope and bring out the video recording gear and leave them while I went off to do my lecture (on global warming!) in Astro 3.

I returned after class and found Becky and Gene were doing well, getting lots of nice photos despite the bright moon. I got the 10" scope up and running without trouble, gave it the coords of the target and I found the star without trouble. Got it in the LCD screen of the camcorder, and 2 minutes before the event, Gene and Becky came out and we all watched the predicted moment - 6:18:31 UT - come and go without an occultation happening. Just as I was about to comment on the recording about the expected miss, the star winked out for 1.777 seconds. Success! Derek got the event also, for 2.0 seconds from his home in Morgan Hill on a track a fraction of a km north of mine. As I write this, there are no other positive chords. Chris had a miss, as did Baldridge at Foothill College and a few others. And Walt Morgan's two stations were also misses. Derek's track was quite close to mine, so the fact that his event was 12% longer than mine suggests either a lumpy asteroid, or that we were close to the southern limit.

Me, Gene, and Becky with my timing gear, just after a nice success

Becky and Gene, imaging a planetary nebula inside the 12" Observatory's "warm room", with standard red-lights on for observing. The non-red computer LCD screen illuminates Becky's and Gene's blue jackets.

A fun night of astronomical success deserves multiple photos...

....victory is sweet! My first successful asteroid occultation of 2011

Here's the IOTA report for my station and for Chris Kitting's IOTA report

Tangra plot, using just the target to follow and not the faint companion. No gamma correction input.

LiMovie plot, using the faint companion star to guide with. While that was a bit jittery during the time the bright target was unocculted, the tracking was good during the critical frames of the D and R, when it's really needed.

Derek's LiMovie output

Below is the analysis from OCCULAR on the .csv file output by LiMovie.

The distribution of errors is pretty Gaussian - a good sign of good quality data

Brad Timerson then generated the sky plane plot of all of our observations. We are able to rule out the validity of the 66 km diameter determined from IRAS satellite data, and the smaller predicted diameter appears to be the right one.


Brad tried to fit the observations to a circular profile here.

Looks like Derek's and my observations rule out the IRAS-derived 66 km diameter and so the smaller 25km diameter was fit to our timings, which, again, unfortunately lie almost on the same track.