Robert Vanderbei's observation and images of the near-grazing occultation of Good SAO 165346 on 2005 Dec. 7
The star appeared quite bright with a ToUcam camera with a 10" RC 10 km n.w. of the limit in Princeton, NJ
New: 2005 Dec. 9
From: Robert Vanderbei [rvdb@Princeton.EDU] Sent: Friday, December 09, 2005 9:50 AM To: Dunham, David Subject: Re: SAO 165346 graze video recorded from Chester, Maryland Hi David, I made a webpage that has images of both the disappearance and reappearance. I reported the times below as +/-0.5 seconds because I used the time-stamp on the file as a mark for the end time and then I counted backwards from there. A few hours before the event, I synced my system clock with NIST so I think my clock was accurate to a few milliseconds. I have since used software that allowed me to see the NIST time to a millisecond, so now I have determined the times to the +/-0.1 precision allowed by the frame rate; the more accurate times are on my Web site with link above. The star is bright in the two images because I stacked several frames. The first one is a stack of 192 frames (ie about 40 seconds of video). Since the dark side of the moon was utterly featureless, there is no noticeable blurring of details. The second one is a stack of about 20 frames (or maybe even less, I forget). Here, I had to use fewer frames to keep the bright side from trailing. I just posted frames 189, 190, 191, and 192 as individual frames on the webpage above to show the disappearance sequence; the reappearance was much more abrupt, not visible in one frame, and full in the next. I took your advice to use my 10" RC instead of my 3.5" Questar. That was good advice. The occultation of SAO 165346 was easy to record on my ToUcam. A friend, Rus, who was interested in visual observation, came over for the occultation. I set up the Questar for visual observation. He set up his binocs on a tripod. Because my 10" RC is not very portable, we observed from my driveway. That put us 10.2 km from the center line---on the north side. The coordinates of my location, calculated from the Google map, are Latitude 40.450931, Longitude -74.655425 (+/- 100 feet). (I have a GPS receiver so I could provide an alternative fix if needed.) That was apparently too far from the center line to get much interesting. The star disappeared at 18:46:11.6+-0.5 and reappeared at 18:55:00.6+-0.5. Frame rate was 5 fps. Individual exposures were 1/25th second. I tried 10 fps, but the star was quite faint at that rate (I don't know why the brightness changed since in both cases the exposure time was 1/25th second---perhaps the ToUcam accumulates multiple exposures for each download.) The disappearance was somewhat interesting. On frame 189 (and all earlier frames), it is there. On frame 190, it appears to be about half as bright as on the previous frame. On frame 191, it is almost gone but one can still see it. On frame 192, it is completely gone. I thought that, for each frame, the star would be fully there or completely gone. So, I was surprised to get those two frames of intermediate star intensity. My first thought was diffraction effects. But, the reappearance 9 minutes later seems to indicate otherwise. The star reappeared all at once---on one frame it wasn't there, on the next it was. Rus tells me he was able, just barely, to see the star through the Questar both before and after the occultation. However, it was very challenging requiring averted vision. It was too difficult to have visually been able to notice multiple disappearances and reappearances. So, it was good that we didn't attempt the observation from a remote location. -- Bob Robert J. Vanderbei http://www.princeton.edu/~rvdb "I sleep in the daytime, I work in the nightime, I might not ever get home" -- Talking Heads