Hodgson Observatory

But having done this rescue of the valuable telescope, the challenge was not over. There were two immediate consequences of this accident: (1) the optical alignment of the big telescope had to be reestablished, using a special

The second consequence of the accident (2) was that the very good Argo Navis alignment made last January was invalidated. Thus we needed to re-align the Argo Navis computer with the realities of the night sky. We had problems getting a good fix on our second alignment star (Altair) — the hazy sky conditions in the

On Monday evening, June 18 (CDT) JJ returned to Hodgson Observatory late afternoon to fix the big Obsession. (He brought his own Obsession along but never unloaded it.)  The trees at Sunniside largely sheltered the Observatory from the strong NW winds of the evening, and the skies were largely clear most of the evening and night. The telescope’s optical alignment was the focus of attention. It was immediately clear from an examination with the

The secondary mirror also needed to be on a longer 3/8th inch bolt than its original. We had no spare longer bolts in inventory, so we pulled one over-long carriage bolt out of a Observatory roof track support (substituting a shorter bolt pro tempore), hacksawed its end off, and attached the secondary mirror to it. Then the secondary mirror was repositioned, and carefully checked with the LaserMate laser, then tightened down, rechecked, readjusted, retightened, rechecked, readjusted, retightened, etc. JJ is a perfectionist when it comes to optics – one of the best in

Then we went on to the primary mirror, guided by the LaserMate device. The primary mirror was rehung in its supporting strap for better support. Then it was adjusted inward until all of the big mirror was reflected in the secondary mirror and was being received by the eyepiece. The track of the laser beam through the optical system then hit the tiny cross in the exact center of the big mirror. Then everything was tightened down, rechecked, adjusted until perfect, then tightened down, rechecked, etc. You know the
litany. It goes on until the rechecking with the laser shows the last tightening has done no harm whatever to the alignment.

It was then sundown. We thrilled we had gotten the optical realignment achieved, and achieved before dark. The view in the big telescope had never been as good.

We paused for coffee and brownies at the house as night fell. Then back at the telescope we did the necessary star alignment for the Argo Navis/ServoCAT system. We used Polaris and Spica in the southwestern sky as alignment stars, centering them initially in the field at 84x, increasing power to 201x, and re-centering, then sending the location by wireless to the Argo Navis. Almost magically, at the same time, JJ managed to achieve
the best optical alignments ever of the 120mm f/8.3 refractor which rides on top of the Obsession, and of its 8x50mm finder scope with that of the big telescope. We were both thrilled.

This resulting star alignment for the Argo Navis initially was an only fair-to-good one. That was not good enough. We wondered if we would have to go back to square one an repeat the job. Then JJ did something not mentioned in the literature that was brilliant. While the Obsession was tracking the sky, he suggested we do an extra star alignment, this time using Altair in the eastern sky. I centered Altair in the center of the field at 201x and called out to JJ who immediately hit “enter” at the console. (We found that using the wireless in this case with the telescope already running did not work, but with a second person at the console, it could and did work.)  In effect what we had done was to substitute in Argo Navis’ mind the Altair data for that of Polaris which lacked the precision we needed.   ALL ARGO NAVIS / ServoCAT SYSTEM OWNERS SHOULD BE AWARE OF THIS TRICK!

By midnight (and a second round of coffee at the house) we were ready to do some testing on several objects to see how well the Argo Navis system was aligned. We ran several objects, using a fairly narrow field

Just for your information, the next SEAC New Moon Saturday gathering will be held at Hodgson Observatory in rural Beresford, SD, on July 14.  In August it will be held in the same place on August 11. Mark your calendars and plan to join us if you can. More details on these events will be sent later.

Remember also that the 2007 South Dakota Star Party will be held on the Hodgson Observatory grounds from Friday, September 7 to Sunday morning, September 9.  Keep checking the SEAC website for more information as the annual SD Starry Party draws closer!

Wishing us all clear skies, Dick Hodgson

Last night was one of the best. Cloudless, almost windless, low humidity, temperatures declining slowly into the upper 50′s F. Seeing was very good although we were not focused on very high magnification work. Totally gone was the haziness of the past week. At midnight a joint examination of the bowl of the Little Dipper (Ursa Minor) showed stars clearly down to ~ +6.5 magnitude against a black sky.

John Johnson (“JJ”) joined me about 7:30 p.m. and set up his 508mm (20-inch) Obsession ENE of  Hodgson Observatory. Then he installed the Student version of “The Sky” astronomy software in the Observatory computer (the one located in the alcove (i.e., “The Cave”).  Then the Sun set.

After a brief coffee break at the house, we commenced operations about 45 minutes after sunset. The Argo Navis / ServoCAT alignment secured last night proved to be very good, well within the mark using the 38mm 84.6x primary eyepiece.  (See a separate e-mail called “635mm (25-inch) Obsession Telescope Repair & Upgrade” for the story). Here we recount briefly highlights of this exceptionally fine night for observing.

JJ looked at a considerable number of Messier and New General Catalogue (NGC) objects. He tended to look often at objects fairly close to zenith. After initial set-up, JJ’s telescope showed a magnificent view of the Great Globular Cluster in Hercules, M13, the finest globular star cluster in the northern hemisphere, containing about 500,000 stars. This was followed by a fine view of M27, the Dumbbell Nebula in Vulpecular, an expanding nebula resulting from a stellar explosion in its central star a few thousand years ago.

A highlight of the evening for both of us was Jupiter. Three satellites were visible initially, but a fourth emerged from behind the planet in the late evening. Using a 42mm eyepiece borrowed from JJ (yielding 78x) and comparing it with my own 38mm eyepiece (84.6x), Jupiter at low power was very impressive in the 635mm (25-inch) Obsession. Atmospheric belt details were exquisite in both eyepieces. Wow!!  The satellites were seen as beautiful round spheres, with no effects of coma or optical distortion, probably the result of very good seeing conditions, atmospheric clarity here in South Dakota, and the new optical alignment of the telescope recently achieved. At 201x (

The other highlight of the evening for both of us was the sight of the TWO brightest component super-galaxies in the Great Hercules Galaxy Supercluster of tens of thousands of galaxies, NGC 6166 — the brightest of all – and NGC 6160, both well seen in JJ’s telescope at 120x in spite of the waxing crescent Moon. Both of them are ~ 430,000,000 light years distant (based on a 71 km/sec/ Megaparsec value for the Hubble constant). That takes us back to the end of the Ordovician Period in Earth’s geologic history, a time
shortly before life began to live on land and breathe Earth’s atmosphere! Wow!   (I had seen NGC 6166 previously as mentioned in an earlier note, but never NGC 6160. JJ had seen neither previously.)