Wednesday, January 26, 2011

The primary mirror is here

Two days ago, the event for which I have been anticipating for nine months had finally took place, the arrival of the primary mirror. The mirror was made by Optic Wave Laboratories, an optics company in California for a cost of just over $2,200. Now that it's here, I installed it temporarily in the mirror cell so I can determine the length the truss tubes have to have. Once that is done, the mirror will be returned to it's storage box until the telescope is ready for star testing.

According to the lab, the mirror has a P-V accuracy of nearly 1/9th wave in the wave front, and a Stehl ratio of 0.952, more than good enough for great views that are "diffraction limited." In other words, the only thing that should limit what is seen is the wave nature of light itself. Because of that, mirrors do not  have to be perfect, just made well enough to offer sharp views. The glass the mirror is made of is Pyrex, a low-expansion glass that will minimize distortion due to temperature effects.

Installing the mirror was straightforward, but the design of the cell I used results in a tight fit. Some spacers will be needed to leave space for the collimation bolts to screw in or out as well, but overall the cell appears to work well. To keep curious cats out of the mirror box and off the mirror, I left the cover on it then placed a heavy battery on top of that to prevent Merlin, the youngest and most curious of them from moving it.

Now that the mirror is here, in a month or less I plan to have the telescope fully assembled, tested and in operation. The mirror will reside permanently in the mirror box to minimize the risk of breakage or other damage befalling it. I could even wash the mirror while in the mirror box, after removing all electrical  and electronic components in it first. The clips have rubber bumpers and the side pins are surrounded by wooden dowels to pad the mirror from bumps and jars during handling, they will not touch it while I'm observing.

Saturday, January 22, 2011

Secondary mirror installed

Now that the primary mirror is due to arrive here the coming Monday, I have taken the secondary mirror which has been in storage for more than a year out of it's protective wrappings and installed it in it's holder. After inserting the mirror into it's aluminum sleeve, I inserted the dew heater for it next, then polyester batting. It then took replacing the four screws to secure it to the hub and keep the very fragile, and expensive too diagonal mirror in it's cell. The mirror will now remain there until it becomes necessary to disassemble the cell again, but because the batting is not a food source for fungi and other organisms, the mirror could be washed right in it's cell without harm to it, the heater or the holder.
Another  task completed was the location and drilling of holes in the front rocker board so the battery holder can be bolted to it. Three of them are free and clear, the fourth lies right above the battery for the cooling fan, which requires the use of a threaded insert. That is a minor problem that can be rectified for the cost of a few dollars and ten minutes of work. With the mirror box and the primary mirror in place, the weight of the battery will not make the rocker box wobbly.

Tuesday, January 18, 2011

Battery position

Now that the primary mirror is due to arrive any day at my home, I have another matter that requires attention. In order to power all the dew heaters and the digital setting circles too when I acquire them, I need a 12-volt DC power source. I already found a way to power the cooling fan, but I also found there is no way to fit enough batteries or a single battery powerful enough for everything in the rocker box without the tailgate bumping into it.

So I got out my welding machine and some 10-gauge flat mild steel stock, and spent two hours measuring, cutting, fitting and MIG welding a battery holder for a separate 18 amp-hour, 12-volt battery that will power the dew heaters and the digital setting  circles independently of the cooling fan, which will draw little power on it's own even at full speed.

What emerged was a holder that will be bolted as low as possible to the front board of the rocker to prevent tippiness. A cable will then run from the battery to the Dew Buster, from which power will be fed to the dew heaters and the digital setting circles. After all the welding and clean up was completed, I sprayed it first with a metal primer, then glossy black enamel paint to prevent rusting.

Sunday, January 2, 2011

More fall and winter objects

In early December the weather and the moon were favorable for a few days for observing deep sky objects. The weather the weekend after that was poor but nevertheless permitted observation of yet more galaxies and nebulae. Most of the objects I concentrated on were galaxies in the constellations Sculptor, Cetus, Pisces and Fornax, but I also looked at objects in Andromeda, Eridanus, Perseus and Cassiopeia. As before, I took my 10-inch Dobsonian to the usual landing strip to observe these objects, because none of them would have been visible from my home.

The first object is the faint and nearly round planetary nebula IC-289 in Cassiopeia. It's only about as big as Jupiter in apparent size, with a dimmer center that made it look a little like a ghostly smoke ring. This object is very tough to find because it's faint, no brighter than 13th magnitude and because of it's small apparent size easy to miss while sweeping the area. An eyepiece that gave a magnification of 150X and an Oxygen III filter made this difficult object for my local skies appear out of a star spangled background sky. Passing clouds merely made it even more time consuming to locate. Without the filter, the nebula was invisible, but I am sure from a very dark site it could be found without any nebula filters at all. Higher magnifications only caused it to become even harder to see.
Next was the Sculptor galaxy NGC-148, which is an edge-on lenticular sytem. These are disk shaped galaxies without spiral arms or large amounts of interstellar gas and dust out of which new stars form. As such it was fairly small, spindle shaped and fairly bright with a brighter center. At 188X it was easy to locate.
NGC-151 was another easy object. Unlike NGC-148, this galaxy is a barred spiral galaxy much like our own Milky Way. Although small in apparent size, it stood out from the foreground stars, with it's dense nuclear bulge apparent. No signs of the vast spiral arms were visible other than an oval disk around the nuclear bulge. This eleventh magnitude object benefits from high magnification, and should be visible through smaller telescopes from dark sites.
NGC-175 is another fairly bright Cetus barred spiral galaxy. It's face-on orientation shows the nuclear region as a brighter core surrounded by a fainter glow where the spiral arms are. Despite being smaller and fainter than NGC-151, it was still easy to spot and did not fade into the background sky at 230X.
NGC-210 is a bright, face-on spiral galaxy in Cetus. It's much more like the Andromeda Galaxy or M-81 in Ursa Major than our own, since it does not have a central bar from which the spiral arms extend outwards. Instead it has a very large nuclear bulge and spiral arms festooned with regions where star formation is ongoing. Indeed, they form a ring around the nuclear bulge. It shines at nearly 11th magnitude with the central core being most visible. The spiral arms and disk are much fainter and much of them was not seen, leaving the galaxy to appear as an oval object with rapid brightening towards the center at 188X.
NGC-254 is another spiral galaxy resembling the nearby and very bright M-81 in Ursa Major. The nuclear region is distinct and the disk is also quite bright in this compact galaxy. At 12th magnitude, it's small apparent size makes it much easier to see than it's apparent faintness suggests as 188X.
NGC-357 is another compact barred spiral galaxy with a large core and bar, and a small disk. Thus it dominates the small, round disk this galaxy appears as at 188X. It's fuzzy, comet like appearance at lower magnifications revealed it's presence. Once again it's compact size made it more visible than it's being nearly 12th magnitude suggests through the murky skies in my area..
This galaxy is different from the galaxies described so far, because it is an elliptical galaxy. These are systems made entirely of older yellow and red stars, with no blue giants and very little gas and dust. NGC-491 like many elliptical galaxies is a nearly round, featureless object, much like a super sized globular star cluster but with billions of stars instead of the million stars a large globular cluster would have. This galaxy was very tiny, almost star like when I came upon it. Despite the apparent magnitude of 13, the apparent size of 1.5 arc minutes made the surface brightness of this galaxy more than high enough to overcome the murkiness in the sky.
NGC-636 is another Cetus galaxy which is fairly bright and easy to see with a modest telescope from a fairly dark site. Like NGC-491, this system is an elliptical galaxy with no active star formation in progress due to the lack of interstellar gas and dust. It is however much brighter and larger in apparent size, and consequently easier to see. Like many galaxies, it looks very much like a distant comet or unresolved star cluster, with a bright core and a fainter halo around it at 230X. Like many galaxies of it's type, NGC-636 bears higher magnifications well.
NGC 467 is one of many elliptical galaxies in Pisces that is in range of 8 and 10-inch telescopes from good sites. Resembling a distant and unresolved globular cluster or faint comet, this is a very distant galaxy that in photographs is attended by a very faint edge on spiral galaxy, which was too faint to see through my telescope that night. It's small apparent size results in a high surface brightness and therefore it's quite visible even though it's a 12th magnitude object.

This barred spiral galaxy in Sculptor is another small but pretty bright object for its apparent size and magnitude. The nuclear region and central bar appear as a brighter core with a fainter oval halo around it being the expansive spiral arms of this more or less equal to our own galaxy. It was surprisingly visible despite the low elevation and murky skies at 188X.
NGC-1097 is one of the best and  brightest galaxies of the southern skies, and even from the northern hemisphere it is well worth looking for with a modest telescope. Located in the constellation Fornax, it shines at ninth magnitude and spans an area of sky almost half as wide as the full moon. It also has a dim and small companion in the outer halo or disk, which went undetected when I looked for it. Due to the low elevation this magnificent barred spiral resides at from my country, I was only able to see the inner regions of this galaxy but it is very bright and visible in even a small telescope. I had no trouble locating it with a 6-inch reflector on several occasions.
The last object I sketched was NGC-1201, another Fornax galaxy that's much smaller in apparent size but much more concentrated and compact than NGC-1097.  That makes it look brighter than NGC-1097 even though it's more than a magnitude dimmer, making this galaxy a good one for small telescope from more southerly regions of the world. The core is very bright and large, while the disk of the galaxy is also bright and oval in shape. A nice example of a bright galaxy that stands up well to high magnifications and doubtlessly would show a lot of detail in bigger telescopes at even higher magnification.