My encounter with the Horsehead...
Posted 09 February 2013 - 05:35 PM
My first target was Jupiter. The GRS was almost at transit. At 100x, there was much detail to see, including the ruddy colored area in the center of the GRS, as well as the partial band that appears to be connected to the GRS. The two equatorial belts were showing a considerable amount of detail. The four moons were resolved into tiny disks with very little flaring. There was a little more blue fringing than usual around Jupiter, indicating that the scope was still in the process of cooling down.
Next up was the Trapezium in M42. The four main stars were like tiny little jewels against a background of faint nebulosity. The E and F components were both resolved with little difficulty at 80x.
Since conditions were favorable, I decided to check out the Flame Nebula. The Flame was dim, but easily visible at 60x. It was even better when I moved Zeta Orionis out of the field of view.
I then spent the next hour or so trying to coax the Horsehead out of hiding. During that time, I observed as the nebulosity started to grow around HIP 26816. At first, I could not make out any of the reddish colored nebulosity (as seen in photographs) that serves as the background of the Horsehead. After about forty-five minutes of staring into the eyepiece (along with many intervals of simply closing my eyes gently to both dark adapt and prevent eye-strain), I noticed that faint nebulosity was sweeping out of HIP 26816 and into an area just below and past HIP 26756. I knew that the Horsehead should show up on the boundary of this nebulosity, so I was beginning to feel a little hopeful. I also noticed that the reddish colored nebulosity (as seen in photographs) that runs from north to south and located just to the west of HIP 26756 was becoming very faintly visible. I remembered from pictures where the Horsehead would be located and I concentrated all my efforts there. After about fifteen more minutes, there was still no Horsehead. I tried different eyepieces and magnifications, but 60x seemed to present the best view of the faint nebulosity. I tried one more technique for coaxing faint details, and that was to use averted vision to find stars anywhere in the field of view that were just on the edge of visibility. I then used averted vision to refocus the telescope on these stars. Closing my eyes gently for a few seconds to relax seemed to help me lessen the strain when focusing. At some point, I began to notice that a very distinct inky black spot was popping in and out of view in an area to the south and east of where I was concentrating my efforts. I also noticed that the nebulosity over the entire field of view was beginning to exhibit faint traces of texture, and I assumed that the dark spot was simply part of this texture. Still, there was no Horsehead to be seen, at least where I was looking. About that time, I got to wondering if maybe I was looking in the wrong place. That dark patch seemed to be way too persistent to dismiss. I noted its location within the field of stars and prepared to shut down for the evening.
Before I moved away from the eyepiece, I decided to check out the Flame Nebula one more time (while trying to avoid Zeta and blow my night vision). I assumed it would look brighter, but I really wasn't expecting what I saw. The nebulosity seemed almost bright and the tree-like darkness in the middle of the nebula was very evident. There was very little actual detail present, but the nebula was still very impressive.
I put my glasses back on and looked up at the Hyades to see how well my eyes had dark adapted. I was able to easily see 5.6 mag stars, but that was about it. I took my glasses back off and got the impression of many more stars being present. I can't say how many, since my astigmatism gets in the way and creates a smeared mess. Still, I would have to think that it was an easy mag 6.0 to 6.5 for naked eye.
After getting everything put away, I checked out a detailed photograph showing the Horsehead and surrounding stars. To my amazement, the Horsehead Nebula was centered exactly where I was seeing the inky black patch and not where I was concentrating all my effort! Of course, since there was no detail present, I can't say that I saw anything that resembled a horse's head. I think what I can do is log this as my very first visual encounter with the Horsehead Nebula.
All in all, I feel this to be a real accomplishment considering I was observing from a location that is in the middle of a yellow zone using an inexpensive 102mm achromatic refractor that I permanently stopped down to 90mm.
As a side-note, after reading back through all of this, I'm left wondering how much, if any, that my color-blindness contributes to what I can or can't see.
Posted 09 February 2013 - 08:14 PM
Which scope did you use and were you using a filter for your Horsehead observation? Regardless, your patience and technique at the eyepiece is marvelous and shows what determined effort can do - well done.
Posted 09 February 2013 - 10:19 PM
I've been chasing the Horsehead for quite awhile using a Celestron C8, but as of yet have not been able to get there with that scope.
The scope I tend to use most often, and the one I used here, is a fairly recent Celestron C102 achromatic refractor that I purchased used as an OTA. I was very disappointed with the performance when I took it out the first few times. It never seemed to achieve sharp focus and the residual color was awful. I purchased a v-block filter, and this did help with the residual color, but I didn't care for the yellow cast. I was going to get rid of the scope, but after doing a little research, I decided to investigate, and I'm really glad that I did.
The problems that I found included a focuser that was pointing at a spot almost at the edge of the objective. It was so far out, I had to remove the focuser assembly and file the holes in the tube to create adjustment slots in order to get it centered. I then cobbled up a Cheshire eyepiece from various items I found around the house. This showed that the objective was way out of collimation The two circles that should have been one circle in the middle were separated by half the diameter of the objective. Since there was no provision for collimation, I had to come up with some way to square it properly. I removed the air-spaced lens from the cell. I was careful to mark the two elements as to their orientation to each other and to their placement in the cell. Examination of the cell showed that the cell was not squared properly when the second side was machined. I had to shim the cell in order to square up the objective. I also drilled and tapped the threaded portion of the cell where it attached to the tube for set-screws. I did this for fine collimation adjustment.
After reassembly, I was able to collimate very closely using the Cheshire. Detail that was lacking from Jupiter now seemed to pop. The double-double in Lyra separated easily, but showed that there was still a problem. There was an odd smearing off to one side that moved as the tube was rotated. My investigation of this showed that the tube was not straight. Removing the lens cell and focuser, I found that the middle of the tube was almost .15" off center. Light striking a baffle was causing the smearing effect. It didn't help that the tube diameter was smaller than the objective. I tried to straighten the tube, but it wouldn't budge. I finally settled on stopping down to 90mm. The unobstructed aperture prior to this was 99mm, so I lost 9mm or about 18 percent of the total light gathering power (it is noticeable). In my opinion, however, what I gained in contrast more than made up for the loss of light.
The OTA is now setup on a home-built GEM. My total setup time is less than five minutes with very little cool down time required. Therefore it gets used quite often.
As for this observing session, I was not using any filters.
Posted 10 February 2013 - 12:30 AM
Posted 10 February 2013 - 02:34 AM
Just as impressive is the work you did to get your scope in working order. Most people would have given up on it and sold it, but you stuck with it and found ways to make it work as well as possible. Well done all around!
Posted 10 February 2013 - 10:00 AM
As for the scope, the main reason I still have it is because I didn't want someone else to get stuck with it. Perhaps one day, if I get ambitious enough, I'll remount the lens assembly into a new cell and tube so I can reclaim the lost aperture.
Posted 10 February 2013 - 11:32 PM
Jupiter looked very good, but maybe not quite as sharp as it did Thursday night.
The E component of the Trapezium was very easy at 80x but the F component required 100x.
The Flame Nebula was easy, but not quite as bright as I remembered. It did get somewhat better after about thirty minutes, however.
The nebulosity sweeping out of HIP 26816 toward HIP 26756 was faintly visible, and got somewhat brighter with the passage of time. Still, it didn't seem to develop the amount of contrast I was seeing Thursday night. The reddish colored nebulosity (as seen in photographs) that runs from north to south and located just to the west of HIP 26756 was just becoming visible, so I thought I might stand another chance to see the Horsehead. I thought that since I knew better where to look, it might be easier this time. Unfortunately, the inky black spot I was seeing the other day never materialized, so I finally gave up. There were a couple of times when I got the vague impression that something might be there, but that could easily have been my imagination.
My impression of tonight on a scale of one to ten would have been about a seven or eight, whereas Thursday would have been closer to a nine. They both were very good nights, but I think an exceptionally good night is required to stand a chance.
Posted 12 February 2013 - 04:57 PM
A few nights ago I did a little better with my 18-inch, but from a much less dark site, no better than mag 6, say. This time, I could clearly see the top of the head and the back of the neck (that is, the south and west boundaries of the nebula), but discerning the nose or chin was not in the cards--again, a UHC filter with 20mm and 14mm eyepieces, in the f/4.2 scope (no paracorr).
One of these days, I'll spring for an H-beta filter!
Thanks again for your report.