Friday, December 24, 2010

Finally finished!

I just got an e-mail from the optician today stating the mirror has been finished. All that remains is to add a coating of aluminum then a protective overcoat on top of that. Sometime after New Year's the mirror will arrive here, and that will allow me to complete the final steps on the telescope's construction. That will be first and foremost determing how long the truss poles have to be, and at what angle the pole blocks will have to be set. To do that, I will temporarily install the primary mirror and use a star to find out how far apart the mirrox box and the upper cage have to be. Once that is determined, I can drill the holes and bolt them permanently to the mirror box after returning the primary mirror to it's storage box. I will have to shim the bottoms of the blocks out, and likely shim the pole seats on the upper cage so the poles will slip into them easily before I tighten the wedges to secure the upper cage in place. I will cut the poles two inches too long to give me a margin for error, then I can trim them to the final length that will allow the eyepieces I now have to focus as well as leave leeway for eyepieces I will buy in the future. This way I'll avoid the risk of having to buy more aluminum tubing because I cut the truss poles too short. After these steps are done, the mirror will be pemanently installed in the mirror box and the sling attached to it with double sided tape to keep the sling from slipping off the edge of the mirror. I will then adjust the sling and side pins to support the mirror in the case of the sling, and to leave a 1/8 to 1/4-inch gap between the mirror and the side pins as well as the mirror clips. They serve to keep the mirror in place and prevent damage to it, they will not touch it normally unless the telescope is bumped or I am driving over a bumpy road. After that, I can then start making the shroud to keep out stray light, and the poles can be covered to make both holding them in the cold less rough on the hands and to supress reflections off of them. Many people use black foam pipe insulation for this, but I am going to try to use shrink wrap tubing that is normally used on large electrical cables to cover the shiny aluminum tubing. After all of these final steps are completed, at long last the telescope can be assembled, collimated then receive it's "first light" on a planet or other celestial object. The much larger aperture will make a big difference in how galaxies look, and the best time to see them is going to come soon. By the time February arrives, the M-81 group of galaxies, along with the clusters of them in Coma Berenices, Leo, Virgo, Centaurus and Hydra will be well placed for observation. There is at least 8,000 galaxies in range of a 15-inch telescope, and of those 8,000 at least 2,000 or 3,000 of them are visible in these galaxy clusters at a good site. The rest are distributed all over the sky including the apparently barren regions near the celestial poles. The massive light grasp will result in brighter examples resembling black and white photos from a dark site, with dimmer ones appearing everywhere wherever there's a galaxy cluster in our local region of the Universe.

Tuesday, December 21, 2010

Solstice total lunar eclipse

Last night's total lunar eclipse was the first to occur on the winter solstice for at least several hundred years, making it a very rare event. Since the weather forecast for my area promised at least relatively clear weather, I set up the 10-inch telescope because it had dew heaters and digital setting circles, which my 6-inch is not equipped with. I recently acquired a new dew heater controller called a Dewbuster, a device that pulses the current and also uses a temperature probe to prevent too much heat from interfering with the views due to heat blooms in the telescope. It also conserves battery power, a big plus for long observing sessions when the dew is extremely heavy like it often is here in coastal Alabama. As soon as it began to get dark, I set up the telescope, and turned the dew heaters on.

I was planning to look at Jupiter, Uranus and Neptune before they dropped behind the trees, but the seeing turned out to be horrible and Jupiter was a large, bright squirming blob. The moon looked like I was watching it from the bottom of a swimming pool. I also discovered the digital setting circles were acting in their usual temperamental manner and thin clouds were passing through, so I left the telescope outside and did other things until the eclipse began. It turns out there was a stationary front near my area, and weather fronts create bad seeing and annoying thin clouds. Had it not been for last night's eclipse, the telescope would have stayed inside last night and I would have been reading a book or watching television.

By 12:30 a.m. the moon was entering the umbra or dark inner shadow of the Earth, making it look like a cookie with a bite taken out of it. At last the horrendous turbulence let up somewhat  but the view was still shimmering from time to time. I opted to use a 32mm and a 21mm eyepiece that gave  magnifications of 41X and 63X respectively, until the coma corrector lens started to fog up. After taking it out, I was looking at the moon at 36X and 57X respectively, which is very low power for a 10-inch Dobsonian, but I had a nice view of the increasingly eclipsed moon. At first, the portion that was eclipsed was a dark grayish brown but as the moon passed deeper into the umbra, the moon took on a dark brownish red color. Around the edge of the umbra, the moon took on a bluish gray color. By 1:15 or so the moon was almost entirely in the umbra and by 1:30 it was completely immersed.

During this time the bluish gray color faded and most of the moon took on shades of brownish red. The stars that otherwise are washed out both to the unaided eye and the telescope came out and I looked at the bright star cluster M-35, which was only a few degrees away from the eclipsed moon. I also stopped to look at the sword of Orion, at the heart of which is the great Orion Nebula. As for the moon itself, it took on a three dimensional appearance as it drifted in front of background stars, dozens of which were visible. Normally the full moon is a whitish, glary object that looks flat and two-dimensional to me through any telescope. The huge light gathering power of a 10-inch Dob makes it almost painful for me to look at without a dark gray filter to dim the moon to a comfortable level. I was able to see with ease the moon's orbital motion as the eastern limb approaches then covers up star after star while others pop back into view on the western side.

By this time a most unwelcome visitor appeared for sky watchers like me, clouds. Few in number, they became steadily more numerous as the  eclipse progressed. By 2:00 a.m. the moon was past mid-totality and the eastern limb was beginning to brighten again. The moon made a wonderful sight as it was at the juncture of the constellations Taurus, Gemini and Auriga. The bluish gray color was starting to return as the planet Saturn was finally climbing above the tree line. Then the weather completely went down hill, and the entire sky rapidly clouded and fogged over. By 2:30 it was time to put away the telescope but as I carried the base back into the house I watched the eclipsed moon appear in a break in the clouds. I was most happy to had the opportunity to watch this rare event.