Jupiter, Saturn and Mars

No big breakthrough moments last night, but sessions where all goes as it is supposed to are always enjoyable. I feel that I am “staying in shape” for that elusive perfect imaging night.

The primary equipment that I used for all runs was G11, LX850, and ASI290MM. This setup, polar alignment and collimation held over from the previous night were all good for another night. The only change up was replacing the dew strap with the dew shield/heater. I powered up the equipment before sunset, to include turning the dew heater on high, so starting my session when I came out at 2100 consisted of acquiring my first target, connecting the laptop, and starting Firecapture.

The Astrospheric forecast was for transparency to be average throughout the night, and seeing started off at average, then improving to above average at 0100. The temperature was forecasted to be a few degrees warmer than the night before, and I planned to dress a little more warmly. The forecasted temp and dew point did not completely converge until right before daybreak, but I expected dew to form before then.

The Astrospheric forecast mostly held up, but I don’t think that the seeing improved until closer to 0230 and not by as much as I had hopped. With the slightly warmer temps and being dressed properly, I was much more comfortable than the night before. I had the dew shield/heater turned on since right before sunset. With that and the slightly better dew forecast I didn’t see any dew on the front glass at all during the night.

The temperature was still 49 degrees when I came outside at 2100, and no dew had formed on the table-like dew measuring device (aka metal table) at that point.

My first target was Saturn just as it came off of the meridian. The seeing was ok, but not great, so I grabbed the best focus that I could by eyeballing it and at 2118 I went on to capture 10 RGB runs at 60s/filter with a 750 x 450 ROI. Shutter speeds were about 91ms at 550 gain, which yielded a 95% histogram (I should have traded some of that histogram, say down to 70%, for a faster shutter and higher frame rate). Frame rate was about 10FPS, which yielded about 330 frames per filter for a total of 9,900 frames. Saturn was at 0.58 magnitude with an apparent diameter of 17.86” and elevated 34 degrees.

By 2200, Jupiter was out of the trees, so I turned to it. Again, the seeing wasn’t great, but the GRS was right on the central meridian, so I didn’t want to miss that. I knew that I could come back to Jupiter when it had ascended to a greater elevation and the seeing had improved. I shot 10 RGB runs at 30s/filter with a 700 x 700 ROI. Shutter speeds were about 4ms with about 400 gain, which yielded an 88% histogram. Frame rate was around 100FPS, which yielded about 2900 frames per filter, and about 87,000 frames total. Jupiter was at magnitude -2.91 with an apparent diameter of 49.39”, and elevated 43 degrees. The detail that I could see on the display was not quite what I had experienced the previous night.

It was 2225 when I finished the Jupiter runs. I noted that the metal table was still dry. I covered the front glass and came back inside to wait for the seeing to improve and for Mars to clear the trees. My intention was to head back out at midnight, but I fell asleep (high quality problem) in the chair until 0115.

Returning to the scope, I found that the metal table was dewy, but the front glass still dry. Jupiter had crossed the meridian by this time. I was disappointed to find that the seeing had worsened. The dark bands were not just rippling, but they were jumping from place to place on the face of Jupiter. I watched for maybe 20 minutes and this did not improve. I decided not to bother with a capture and to move on to Mars via a short focusing session on Aldebaran with the Bahtinov mask. After doing the mask focus, I would not touch the focus for the Mars runs. I did check the front glass and found that it was still dry.

An observation regarding the seeing. I have been monitoring seeing as it seems to get worse with humidity. What I saw with my second visit to Jupiter seems to support my hunch that higher humidity portends worse seeing. That the Astrospheric forecast was for above average seeing by this time seems to lend greater support for humidity adversely affecting seeing. But I’ll add that I thought that higher humidity was supposed to calm the seeing. I will continue to watch this relationship.

On arrival at Mars, the seeing was not what I had hoped for. I waited until about 0225 before I started imaging. The seeing had improved a little. I captured 5 iRGB runs at 60s/filter with a 320 x 320 ROI. Shutter speed was about 1ms with about 400 gain, which yielded a 70% histogram. Frame rate was about 573 FPS, which yielded about 34,400 frames per filter, or 172,000 frames total. Mars’ magnitude was -.76 with an apparent diameter of 12.8”, and elevated 50 degrees above the horizon.

I think it is worth pausing here to note the observable differences between the three planets that I imaged, and the image settings. Jupiter and Mars’s were brightest in the negative magnitudes and Saturn was a half magnitude. From an appearance perspective there is a vast difference between Jupiter and Saturn. With regard to apparent size, Jupiter is by far the largest, and Saturn barely beats Mars. And looking at elevations, Mars was by far the highest, and I could have waited for more elevation. Similarly with Jupiter, as it was not going to get much higher than it was at capture. Saturn was at the lowest elevation of the three planets, but it was near its highest elevation for the evening. Jupiter, in spite of the larger and shorter limit per filter yielded by far the highest number of frames. Dimmer Saturn forced setting that yielded the smallest number of frames.

As I shut down the session, I checked the front glass and it was still dry, and I was still comfortable when I came inside at 0300 and saw that the temperature was 45 degrees. 

Saturn - 2022-10-11 01:35
Jupiter - 2022-10-11 02:13 UTC
Mars - 2022-10-11 06:39 UTC

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