The Theobalda Occultation

Nov 7, 2015

Planning page


Chris Angelos joined me for this event, one of the bigger events of 2015, with 13 chords planned out from SF Bay to Tucson, Arizona. I set up at Cabrillo Observatory, planning to use the 10" scope with Watec as is my new procedure. Skies were clear and cold, but a bit damp. The event was at 2:21am. I arrived at the observatory after printing up charts in my office, a little after midnight. I first got the 12" dome computer and scope powered up and running. However, this event was going to be a challenge - the object spend the previous 70 minutes or so nearly overhead and was still 75 degrees up at event time. The 12" scope doesn't point well at such high elevations, and the Meade 10" will not allow the usual f/3.3 + video camera straight through without hitting the fork bottom. I'd planned to try using a diagonal. But first was finding the target. There was a tight 9th magnitude double star not far away so I thought it would be easy. But the pointing was poor and I eventually toggled off the power and did a new 2-star alignment, which at least seemed to point well at M45. But to the zenith, I couldn't recognize the field. It didn't help that I had still not made a field marker in C2A which would show the eyepiece size projected on the chart. That was a critical mistake. Chris Angelos drove up with about 45 minutes to go. I was beginning to rush still trying to find the target, and eventually gave up and decided to bring in the video gear box and gel-cell into the warm room. I was able to feel some confidence I had the field right, in the PC165dnr field mounted on the ST80 finder scope. I got the recording started and waited.... Chris watching the ST2000xcm CCD image of the area downloading every second, and I watching the LCD screen on the ZR45mc camcorder..... and.... no occultation. What? I was on the CENTERline of this high rank event! Odds were 75% for a "hit". But I verified the proper field afterwards and the targe was indeed right in the center of the recording. A miss, from the centerline. All sites north of me (most of the 13 total) also had misses.

I've now heard that Ted Blank in Tucson had a short occultation. My track might be the nearest "miss" chord. A "successful miss" if you will.

I learned that I still had more work to do on fine-tuning procedures, especially for these high-altitude events. My evolving general procedures page is here.

Some long faces, as target-finding at the 10" wasn't going well, even before mounting the videocam

After the event, at least a definitely on-target recording, even if a "miss"

I hadn't realized that Chris had spent such attention to building this very well made OccBox, with TV monitor, wireless communication to the video camera and DVR... well done!

The nicest planetary conjunction of the year was also early this morning, as the crescent moon joined Venus and Mars, with Jupiter not far above. Chris and I drove up to the entrance to the Horticultlure complext for some pictures at 4am

The overexposed moon and Venus above, Mars much fainter just above Venus, and Jupiter at top


Here's my IOTA report on this "miss".