Over the last few years I have taken an interest in the timing of occultations, specifically minor planet occultations. This is a fascinating corner of the world of amateur astronomy where an observer, equipped with rather modest equipment can measure the diameter of an asteroid and if a group of amateurs combine resources they can plot the asteroid's profile. My observations to date have been visual and despite the high accuracy of my GPS timing equipment my timings are subject to vagrancies human reaction. Visual timings are only accurate to 0.1 to 0.2 second and the speed of the projected shadow from the asteroid across the ground is in the order of 120,000 kilometres per hour, the error margin could be in the order of 20 percent of the asteroid's diameter. Not a good basis for scientific observations.
More accurate methods of timing occultations are required and high sensitive video cameras are perfect for this application. There are a number of cameras available that are rated at 0.0003lux and when used with telescopes of 8 to 10 inch amateur the recording of magnitude 10 or 11 stars is within grasp. When combined with a image rate of 25 frames per second and high quality timing signals from the GPS network then here is the perfect solution. This telescope will be my platform for exploring the world of video occultation timing as well as other aspects of video astronomy.
The smoothing and polishing tools.
My machine called Donkey at work.
All grinding and polishing was done on Donkey and it sure was nice to watch the work instead of working leaving me free to get onto other things. Grinding was fairly uneventful, except for a recalcitrant pit that took forever to leave.
Polishing was done in two stages, the first 1 hour session produced a flash polish all over. The second session started at 12:30pm and the tool was not removed from the mirror for the next 10 hours and the machine was only stopped to shift the mirror on the turntable every 1/2 hour or so. I was left with a beautiful black polish and the beam from a laser pointer could not be detected entering the glass.
It was a relief and pleasure to do the figuring by hand and the process went well with 12 sessions to reach a good figure.
As with my previous mirror I set up a shelf in the loungeroom that was at a comfortable standing height and I could leave the tester and stand setup on the shelf. My routine was as follows:
| Last updated - 24nd September 2003 | Return to Dave's HomePage | email Dave (d a v e g @ t p g . c o m . a u) |