[sac-forum] Two Pleiades stars occulted last night (?) -- Doin's at SAC ATM

  • From: Gene A Lucas <geneluca@xxxxxxxxxxxxx>
  • To: SAC FORUM <sac-forum@xxxxxxxxxxxxx>, Randy Peterson <rgpeterson@xxxxxxx>
  • Date: Wed, 04 Feb 2009 10:42:13 -0700

Greetings,

At the SAC ATM meeting at Paul Lind's house last night, Jimmy Ray set up his binocular mirror viewer in the driveway, and we looked at the Moon with his 9x60 binos. There were two bright stars near the Moon... this was about 8 pm, I think.... Got me wondering... after a bit I realized, the Pleiades grazes predicted on "Feb. 4th" were LAST NIGHT, Feb. 3rd MST -- the ol' UT time thing again!! The two grazing occultations were predicted to be visible in the vicinity of Casa Grande, well south of us, just at sunset.... I looked for, but did not spot, the star that was predicted to be occulted ca. 10:30 pm. Probably could not find it because of the streetlights around Paul's house. There is a long series of Pleiades occultations this year, but not many grazes close to Phoenix... These two last night were unfavorable, due to the time, and the later one was for a rather "flat" profile, and would have been visible near Tucson, probably not worthwhile driving that far. Total lunar occultations and grazes are still worth observing and timing. Predictions are available from the IOTA web pages.

Other doin's....

We set up and did a Foucault test on the 1995 Pierre Schwaar mirror from the EVAC 12.5 inch DOB telescope (which I am now Custodian for)... Paul Lind entered the test readings into his software, and printed out a nice graphical plot. (Thanks, Paul !) The test showed that, overall, it is an averaged 1/7 th wave mirror, with a calculated Strehl ratio of 0.9164 (meaning, about 92 percent of the light is focused into the center of the Airy disk, or a very good reading). The most important finding was that the mirror is very smooth, with no bad zones or other adverse indications. Measured R.O.C. is 131.8 inches, for a focal length of 65.9 inches, and an f: ratio of 5.27. It is a full-thickness (2 inches) Pyrex mirror, 12.5 inch diameter, good polish all the way to the edge.

From the discussion and some sketched diagrams, Jimmy Ray gradually came to understand the ideas behind the Foucault test and interpretation of the shadows... Nothing like a "hands on" optics demonstration !

Dave Fredericksen was pleased with the yellow paint on the upper tube section I brought along... (If you have seen his huge pickup truck, you would understand...) I will be doing some work on the scope to improve it a bit, and will try to bring that out to star parties as frequently as I can. I had it assembled and in operation up at the EVAC Boyce-Thompson two weekends ago, and it performed nicely. Good views of the Pleiades with a 56mm Super Plossl eyepiece -- I spotted the Merope nebula easily.

Another fellow (new member - name escapes) brought a 20-year-old, 8-inch Meade LX3 SCT (or possibly a model 2080), which was in serious need of collimation. The "SAC Optics Team" (Lynn Blackburn, Dave Fredericksen, and Jimmy Ray, AKA Curly, Moe and Larry, nuk nuk) fiddled with it (!!) and got it pretty well collimated. Nice images. From what the owner described, the telescope was in very poor condition when he got it (after years of storage under bad conditions), and it had to be cleaned up thoroughly, including the optics. He was pleasantly surprised that it now works so well.

I tried out my Ronchi eyepiece, and it showed test bands nicely on Sirius.

Rick Tejera brought his little 4-inch collapsable Newt (constructed by Pierre Schwaar), and re-cemented the secondary mirror.

As always, lots of good discussion, soda pop, and cookies provided by Paul's wife...

Gene Lucas
(17250)

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