Yesterday was a busy astronomy day, even before getting to the targets that this report covers. Today I set up the GM8/TV/ASI178 for shooting the Moon, and I put the ASI290 non the Meade for shooting the three planets.
On the path to getting ready, I set up to check the Meade’s collimation by putting out the artificial star and pointing the telescope at it at around 1400. Knowing that collimating is difficult in the bright daylight, I came out to actually do the collimation at 1700. There was some residual sunlight across the grass, but it was gone within minutes of my arrival at the scope. The diffraction rings were shimmering all over the place as a result the ground surface still radiating a lot of heat. This caused the center of the unfocused star appear as three for four centers rapidly orbiting about one another. I watched and waited, and everything got steady about half an hour later. I was surprised to find that the center of the unfocused image was about 1/3 of the way between the center and the outer diffraction ring. I made my best guess about which adjustment screw to turn, and that guess was correct.I was able to quicky make the necessary tweaks to get to good collimation. The sky was not dark enough to begin polar alignment when I finished collimating, so I went inside for dinner. What I learned here is that with prior setup, collimation can be done without delaying polar alignment. From now on I will do a collimation any time that the scope has been handled.
When I came back outside at 2030 it was rather chilly with the temperature in the upper 40s already. I put on my heavy blue parka and was just fine. First task was to check PA with PoleMaster. The Meade had settled a little, and the TV was about two degrees off. PoleMaster PA will be good enough for the lunar and planetary work that I have planned.
Finishing up the PA more than an hour before Jupiter came out of the trees, I came inside to warm up. I headed back out at 2130 to begin imaging. The temperature was 45 degrees, and the temp and dewpoint plots were converging, so I was expecting dew. There was no surface wind. Astrospheric was showing average seeing and average transparency.
At 2145 I came back outside to work with the G11/Meade on Jupiter. Its apparent diameter was 49.44”, and it was I could see more Jupiter detail on the FC display that I had ever seen before. Seeing appeared to be better than average, so that could help account for the better image. The Chroma filters and better collimation could have helped with this, which would have improved focus as well. I captured one RGB run on Jupiter with Io and its shadow about to move off of the western limb. After Io was well separated from Jupiter’s disk, I captured another RGB while the shadow was still visible.
Wanting to wait until Io’s shadow had moved off of Jupiter’s disk before continuing with my main capture of Jupiter, I moved to the GM8/TV to capture the moon. At the TV/ASI178 image scale, I could see no evidence of bad seeing. Since the moon is ever so slightly larger than the frame height, I captured one run of the top of the moon and another of the bottom. These two images will be stitched together in PS during processing.
The capture details are two OSC runs (one top and one bottom) with the ASI178. My exposure strategy for this target and this setup was to set a frame limit instead of a time limit for the capture. In this case, I shot 10,000 frames with 0.75ms exposures at 104 gain. The total duration for each run was about 165s. I was getting about 60fps capturing the full frame instead of selecting an ROI. The capture time was around 2300, at which time the Moon was about 1.5 hours before the meridian and 45 degrees elevated above the horizon with the Ra being N5 degrees. The Moon was about 2 degrees below the ecliptic. At 15.0 days old, it was 99% illuminated. Its apparent diameter was 31’54”.
While on the Moon, I found what appeared to be something pushing the scope slightly to one side, then releasing. This was accompanied by an audible tick that seemed to be coming from the Ra gearbox. My guess at the time was that the Oldham coupler was binding, but I don’t think that it turns that fast. I’ll need to investigate this.
Moving back to the G11/Meade to shoot ten RGB runs on Jupiter, it was about 90 minutes before the meridian. It’s Ra was just below the celestial equator. This time I remembered to verify that the filter wheel was actually turning, and found that it was not, and I might find that the filter wheel did not rotate during the first two runs that I did on Jupiter. I found the cause was a driver error that I was able to clear by restarting the computer. I think that this error popped up as a result of switching between the monochrome (needs filter wheel) and the OSC camera (does not need filter wheel), or perhaps switching improperly. For example, maybe I should have closed and re-opened FC between captures. I also found dew on the front glass of the scope. Expecting dew, it would have been prudent for me to have covered the Meade while I was working on the TV. I put my finger under the dew strap to verify that it was warm, and it did not seem to be warm at all. It occurred to me that maybe the warmth that I could feel when the scope was 65 degrees might not be discernable when the heat is being more rapidly conducted into the 40 degree scope.
The ten runs were shot at 30s/filter through the RGB set. Exposure was about 3-4s and gain was about 325, which resulted in a 80% histogram. With a 720 x 710 ROI, I was getting around 100 fps, which yielded about 2900 frames per filter.
I slewed to Uranus to see if it had cleared the trees, and not only found that it had, but it landed in my FC display without having to hunt it down. I was so excited about having landed on it that I forgot to check the front glass, which I am sure was already getting dewed up again. Going to normal exposure settings, I found Uranus to be a shimmering mess due to worsening seeing, but I captured six RGB runs since I was already fairly well invested in this target. I was shooting 60s/filter with an exposure duration of 81.5ms and gain 450. This yielded a 12 fps for a total of 730 frames per filter and histogram of 85%.
Before leaving Uranus, I captured 20 1s exposures at 600 gain that were highly over exposed to reveal Uranus’ satellites.
My final slew was to Mars. Fortuitously, I had left Uranus’ highly over exposed capture settings in Firecapture. Because of this I saw one of Mars’ satellites to the east of the planet as it settled into the FC display. I checked in Stellarium and found that it was Phobos. This is something that I never expected to see in my life! I then slewed to the west side of Mars where Deimos was supposed to be and there it was as well!
Unfortunately, I was under time pressure because of the dew situation, so I captured five iRGB runs on Mars before coming back to the two satellites. The reasons why I shot just five runs were that Mars looked too crappy for me to invest to much time on this target. Also, I had doubled by exposure limit to 60s, and was getting about 35 frames. Exposure duration was 1ms and gain 400. ROI was 730 x 730, which at a 68% histogram yield 570 fps for a total of 35,000 frames per filter. Mars was elevated 55 degrees and presented at nearly 13” apparent diameter at the time of this capture.
While setting up to capture Mars’ satellites, found that I could bring out Phobos and Deimos a little better at 1.2s so I went with that. Mars itself was a huge bright blob that wanted to wash out the entire frame at this exposure setting, but I found that I could improve the contrast on the satellites by moving it off of the edge of the display.
I finished my work at the scope and came back inside for good at 0300. The temperature was 41 degrees, and the dew on surfaces was approaching Farm quality. By the end of the Mars capture, I was getting very cold. Even though my time outside was rather brief, I should have been dressed with more layers.
Here is what I learned from this session:
A pattern that I have noticed over the past two sessions is that seeing will be pretty good at first, and then decline as the dew gets worse. For some reason I was expecting better seeing to accompany high humidity, but that may not be the case. I’ll keep an eye on this relationship in future sessions.
I may be surprised at what satellites of other planets can be brought out with 1s and longer exposures. I look forward to experimenting with this.
With prior setup, collimation is fast and easy, and should be done before using the scope any time that it has moved.
And here is a to-do list:
Looking at my log files to get exposure parameters, I was reminded of some FC settings that are somewhat hidden. I will send you those on top of the email that walked you through your initial FC setup. I eventually want to include all of the settings in a planetary capture guide.
Check to see if the dew strap is heating
Check the GM8 tick/jerking motion
From yesterday afternoon into the early hours of this morning I have had what is perhaps on of my most demanding astronomy days ever. This was not just the capture, but the setup, preparation, and session management. I had to fight through a great deal of fatigue to stay on my game, and to keep leaving the warmth of the house to come back to the scope. That’s right, this was a fantastic day! Although everything wasn’t “guns-n-roses” (sic) tonight, I am better prepared for my next session.
