Re: Three extraordinary planet nights

Roy Diffrient

Thanks Mark – sounds like a great one.


On Aug 26, 2021, at 8:03 AM, jimcoble2000 via <jimcoble2000@...> wrote:

For the past three nights the seeing has been excellent to perfect as of last night. Kent and I spent about 9 total hours observing Saturn and Jupiter. While the first two nights were quite good, last night was one of the best nights for observing planets in the past two years. Under fairly warm skies with up to 90% humidity. There were only a few passing clouds. This offered the possibility of exceptional solar system observation and it did not disappoint.

Saturn was observed with two 5 inch refractors and a wide variety of eyepieces and combinations. By ten in the evening, we had spent about an hour and a half of observing the ringed planet. Planet bands were excellent but the rings put on the show last night. Under fairly high power we were able to distinguish not only the usual Cassini division we were able to detect the Enke division which is much smaller and requires considerable power and seeing. Most of the time you sensed it but at the best of moments in seeing, we both could distinguish the gap for a fleeting second. This was under perfect seeing mind you. This is when the rings look like grooves in an old LP record. I have done this one or two times previously. Both times we were using 268 to 300x. We also saw five moons even under suburban skies. The C ring was obvious also.

But the best and what I consider our  finest observation was yet to come.

Around 1020 we shifted to Jupiter which was now high enough to do good work. I will skip the usual observations, fine as they were, and get to the best observation of my multi decade career of observation. I know it was a high point for Kent also.

By happy coincidence two of Jupiter's moons were in a very close conjunction. Io and Ganymede were within 2.5 arc seconds of each other. This offered the opportunity to achieve comparative close observations of the two moons. The other happy consequence was that these two moons are a study in contrasts. The first thing you noticed at 300X was the significant size difference as the two moons were next to each other, resembling a close double star. Normally you can distinguish size differences on any good night of looking at the 4 main satellites of Jupiter but it really becomes obvious at such close separation. But the real highlight was this.

The best coincidence of the conjunction is that Io is the most volcanic body in the solar system. It is dominated by vulcanism repaving itself constantly. It has few craters, a universal feature of solar system bodies that are not gas giants. It is also distinctly yellow/orange in photos. Ganymede is quite bright with some dark regions. Overall it has a fairly high reflectance or albedo due to icy it's composition.

It occurred to me this might be the chance to use very high powers, 700X, to see if this difference in the moons could be detected. Close proximity, perfect seeing, and high powers offered a chance at an unusual opportunity. I cranked it up the 700x using a 1.6mm Vixen. I was thrilled to see the difference in color instantly. Io was a distinct orange in contrast to a bluish white tint of Ganymede. I called Kent over to observe without telling him what we were doing. As he looked I asked him "quick, what are the colors"? He nailed it instantly. We both have a lot of experience in subtle double star colors so Kent was an ideal test bed.  He had no hesitation in the observation. We had actually seen color and albedo difference in what are always just white orbs during normal observing. Combined circumstance allowed us to make what I personally consider my best, or at least extraordinary, observation visually ever.  What a climax to three excellent planet nights.

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