Christa

The Occultation of a 9.3 magnitude star by the Asteroid Christa

July 13/14, 2018

This is the event around which we're building our summer Astro 25 class The star is, for these sorts of things, quite bright - magnitude 9.3 - and therefore should not be hard to locate and get good data for. Our plan is to try to get this from two stations. One will be our campsite, and the other will be some miles away, set up by me south of the campsite, perhaps closer to the CaneBrake/Main road intersection. The star will disappear behind the asteroid for just a few seconds, and the edge of the path is not that far north of our campsite, so getting a second station will be very valuable to precisely pinpointing the asteroid and determining it's exact size.

There's a new "app" for iOS which will also make it easy for visual observers to get good timings. More on this later, but basically, you use your iphone to record video of a person as they look into the telescope and wait for the star to disappear, and record him shouting "D!", and then "R!" a few seconds later. Each frame of video will be time-stamped to a few milliseconds accuracy. It's a great backup for the more sophisticated system I'll demonstrate with the IOTA VTI and Watec 910hx video camera.

I'm hoping that Kirk and JP will also be involved, and also we'll see if we can bring a second Celestron video-equipped telescope for this.

There's how the asteroid occultation path crosses the United States. At thie point, in mid May, there is one other observers - Steve Messner in Minnesota. There will likely be others for this favorable event as the time gets closer

The green line is the predicted centerline for the path. The blue line north of camp is the predicted northern limit. The actual path has an estimated 66% chance of being inside (south of) the red line, and our odds of a "hit" at our camp are calculated to be 74%

Field of view for Dobsonians (but image rotation will be different depending on how you hold your head and telescope tilt!

Field of view for the 8" SCT's with Orion Q70 eyepiece circle drawn, about 1 degree Field for this eyepiece. Target is in the center of the circle at magnitude 9.3. This system has 3 mirrors and so is left-right inverted. For those using an SCT in alt/az mode, this is the proper orientation and size for 32mm Q70 eyepiece

Field of view on the Watec 910hx chip on the Canon ZR45mc camcorder LCD screen (box). This is "straight through" a 2 mirror system, so not left-right inverted

The target is in the middle of the handle of the "Teaspoon" formation just above and left of the Teapot of Sagittarius. The altitude will be about 32 degrees in the south

Results:

A passing cloud covered the target starting 20 sec before predicted D, and lasted for several minutes. "Nasoned"!