This past week has been busy with work on several small details and one major step.
Sunday 20 Feb
The planetarium software that I use (TheSky6) allows a local horizon to be defined so that the display of the sky can be masked to represent the view from your viewing location. I did this a couple of years ago for my open viewing platform. It proved very useful. To achieve some accuracy I built a very crude transit and placed it on top of my tripod at the level where the mount’s right ascension (RA) and declination (Dec) axes of rotation intersected. I wouldn’t use it to navigate to the local Tom Thumb but an object would clear the trees within a minute of when the horizon mask showed it would.
Visible in the above photo is the chimney that obscures some of my northern horizon. Also visible in the photo are some sighting strings I used to find out where the center of the dome actually is in relation to the telescope mount. There is some fairly stiff math needed to position the dome slit directly in front of the telescope and several offsets are needed to fine tune the positioning algorithm.
When I was observing from the open platform I installed some brackets on the deck that the tripod legs would settle into. This aided in alignment and provided a constant location for the observations.
Prior to the construction of the dome, I did two things to ensure I ended up in the same place when construction was finished. After fine tuning the telescope mount to the sky each night, I shot a laser spot onto the side of the house and marked it. This gave me a reference line from the mount to the North Celestial Pole (NCP). This line would be crucial in placing the bolts into the concrete pier footing. The pier has some adjustability as well as the mount, but the net is full of observatory horror stories when a compass and offset were used and the adjustments could not handle the positioning error. The second thing I did was drop a plumb line through the platform and pound a carriage bolt into the ground at that location. This established the center of the pier and thus the desired center of the dome.
We used the carriage bolt references to position the pier footing and the laser references to position the bolts. Based on the sighting strings we got the positioning very close to where we wanted it. Although we established the NCP line right on, we dropped the bolts into the footing 2/16 of an inch west of center. When I installed the dome onto the building, I got the dome 5/16 of an inch east of center. Within the resolution of my measuring devices we have no North/South offset.
Monday 21 Feb
Since the telescope would interfere with the horizon characterization and sighting-in the dome, I had to wait for those tasks to be completed. But Monday evening the mount and telescope were installed.
I set both the pier and mount in the middle of their adjustment ranges and started the alignment procedure. I’ve been using PoleAlignMax to align the mount. It works by querying the mount as to where it thinks it is pointed. The program then takes a series of three images offset from each other by a specific amount. Based on analysis of the images the program displays how far off of the NCP and in what direction the error is. You then adjust the manual alignments and start over. Eventually, you converge on the NCP. The initial alignment was off by 15 arc minutes in Dec and 24 arc minutes in RA. That is amazingly close. Within a half-hour the mount was off by about an arc minute in both directions. There is always fervent discussion as to whether or not to align mounts perfectly. One argument is that the perfect alignment eases the mounts job, the other side says leave some small misalignment to get the guiding out of a null area. My experience is that this mount guides a bit better with a slight misalignment and so will leave it here for now. I will recheck the alignment over the next couple of weeks just to see how stable everything is.
Visible in the above photo is the window and the door into the control room. You can also just see the door to exit the observatory.
Wednesday 23 Feb
I couldn’t wait any longer so I accomplished the observatories first light exposure tonight. The actual first image was a luminance frame for M 46. There wasn’t an overly exciting object in view but M 46 was fine by me. M 46 (AKA NGC 2437) is an open star cluster in the constellation Puppis. What is unique about M 46 is the chance alignment of the planetary nebula NGC 2438. This image is 100 ten second exposures.
Thursday 24 Feb
I had suspected that I would need to install some lighting in the dome room for use when observations were underway. Last night proved my suspicions correct and that they would be needed right away. I purchased a set of 12 volt deck lights from the local do-it-yourself store. I installed them around the perimiter of the room, on the floor, between the exposed 2x6s and turned them against the wall to limit glare from the exposed bulb.
Friday 25 Feb
I took Friday off to meet with the plumber who will install the valves necessary for the camera cooling lines, so I was able to get more done than I could normally do after work.
To start with, I finished the caulking; the building exterior is now complete.
I wired the dome room lighting and installed red bulbs in each fixture.
The consultation with the plumber went well and he will be back Monday to install the equipment. The primary inlet valve will be a sprinkler control valve that I can control remotely (one more part of the observatory automation).
Then after dark I tested the new dome room lighting. I was afraid that the lights would be too bright and I would have to install a dimmer, but the lighting was perfect. The floor is outlined with soft red light but with no detectable glow on the inside of the dome. Then I was able to get some real observations done. I was able to get imagery of minor planets 2011 CG2, 2011 CH71 and 2011 CY46. I processed that imagery and was able to submit my first observations since November 12 of last year. I didn’t think it would take this long.