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Log, Sep 27, 2000

2 staff: With clear and steady skies overhead Joe and Doug scheduled a work session at the dome to install "Bob's Nobs" (custom sized collimation screws) and to perform a thorough collimation of the 16". Removing the dew shield caused a temporary problem, as the scope refused to find HOME. It turned out that the tube balance was thrown off so much without the shield that the system refused to proceed. Joe quickly rebalanced things and the problem disappeared.

Installing the knobs was easy although the screws themselves could have been a smidgen longer. The guys centered the scope on Delta Aquila and gave it a look at 160X - it looked like a little comet, due to the changes the installation had caused to the secondary! Not to worry. With Joe at the corrector plate and Doug at the eyepiece, it was a simple matter to readjust everything so that the out of focus star formed a perfectly concentric "donut". Shifting next to 610X , the airy disc and diffraction rings were inspected. The air in the dome was still stabilizing as the night cooled but some final tweaking resulted in a very good collimation, noticeably better than the scope had been up until that night. Joe and Doug are now confident that making minor adjustments to the collimation in the future will be a snap - aided greatly by "Bob's Nobs".

We decided to do some observing to test the results of our efforts. First up was the often overlooked globular cluster M55 in Sagittarius. M55 is a large and bright, but loosely packed cluster (visually) that the 16" resolved right to the core. Next was NGC6818, a 10th magnitude planetary in Sagittarius known as the "Little Gem". It is indeed small, about 1/5 the size of M57, but has a high surface brightness. Very near to it are some faint field stars that look like sparkling from the "gem". Doug suggested that they next try for NGC6822, Barnard's Galaxy in Sagittarius. This irregular system, about 10th magnitude, is a member of the Milky Way's local group. It was dim in the 16" but the outline of its star patterns was clearly seen and later confirmed by Doug by checking a Palomar Sky Survey photograph.

Joe then mounted our new Oxy-III filter and turned the scope to M17 [Swan Nebula]. Whole new areas of faint nebulosity to the east of the main body jumped into view - neither observer had ever seen this except in long exposure photographs. Next it was on to M8 [Lagoon Nebula]. Despite the low position in the sky, this was the best view yet of the famous, and very large, nebula. Many new swirls of delicate nebulosity were clearly seen. M20 [Trifid nebula] did not benefit from the Oxy-III since it's a reflection rather than an emission nebula.

The next target was the famous Helix [NGC7293] in Aquarius with the Oxy-III still in place. The view was very impressive in the 40 mm Konig, with the large planetary taking up over 1/3 of the field! The circular shape was well contrasted against the sky background and the central hole was very pronounced. Despite the dimming effect of the filter, many faint stars were seen in the center and in the nebula's ring. The magnitude. 13.5 central star was not seen, but probably would have been easy without the filter. Nearby NGC7009 [Saturn Nebula] was impressive and very extended at 610X!

Joe and Doug closed out the night with a test of the optics on the planets. Well placed Uranus and Neptune were crisp at high powers. Uranus' moons Titania and Oberon were seen, as was Neptune's Triton (easiest of the three, despite the nearly 3 billion mile distance!) Saturn was checked, even though it was still low in the East. The air was getting rather hazy and so the planet itself was not especially impressive. Five moons were observed, however (Titan, Rhea, Dione, Tethys, and Iapetus) What was thought to be Hyperion turned out to be a 12th magnitude field star.

Before heading home, Joe remounted the tube derotator and did a full two star realignment - in preparation for the next big public Friday evening.

-Doug Stewart

Leslie Coleman
Author:
Leslie Coleman
Entry Date:
Sep 27, 2000
Published Under:
Leslie Coleman's Log
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