Viewing the moons of Uranus through the eyepiece.

Reports for 2019
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Apollo XX
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Viewing the moons of Uranus through the eyepiece.

Unread post by Apollo XX » Mon Dec 02, 2019 1:01 pm

November was a tough month sky-wise for observing, but we did get a couple of breaks so it wasn't a total loss. One of those breaks came this past Saturday night. A fellow observer and myself had been discussing recently about attempting to visually view the moons of Uranus. With the forecast for the night to be clear, we agreed on a time and place to meet and give it a shot.

Uranus has 27 known moons, but only five are within reach of amateur equipment. The brightest one comes in at mag13.9, with the next three in the 14-15mag range and the last one at 15.6. In preparation for the task at hand I made up some charts to first find the planet, then using the Sky&Tel observing tools I also made a chart showing the arrangement of the five targets at the time that we would be viewing. My friend's job was to bring the big telescope.

I got to the site a little early, so I occupied myself with attempting to bag a couple of more double stars in my DSC60 project. It became immediately evident that we would not be enjoying the most pristine sky on this evening. I was attempting to find a couple of doubles in Pisces, and could see no signpost stars from which to hop off from. Given that I'm using only a red dot finder on this particular scope, the task of hopping great distances by looking through the eyepiece using just a pocket sky atlas can be frustrating, and eventually I just went to viewing stuff that I could find with little effort for the fun of it.

The assembly of the big scope was coming along nicely, and in short order I heard 'ok, I'm ready' from that direction. My charts were made using the head of Cetus as a hopping-off point, but again there were virtually no stars to work with in that field. We wound up hopping down from Aries, and in just a couple of minutes we had Uranus in the eyepiece. We wasted no time. We put in the highest power eyepiece that we had and I stood in the background for several minutes while my friend looked, and looked, and looked. On some level I was expecting faster results than this. And it continued - silence. He stepped away from the eyepiece and I moved in. I now understood the silence. Except for the planet and a relatively bright field star there was nothing in the view. The background was rather bright from the poor sky quality and the bottom-of-the-barrel seeing was making focusing a constant task. We had a challenge on our hands.

Eventually something did show up in the view, and at first we though it was Titania, the brightest moon of Uranus. As often happens in these situations though, the true scale of what you're looking at isn't fully understood and it turns out that what we were seeing was a actually a field star in the 14-15th mag range. The fact that it wasn't one of the moons only became clear after Titania and Oberon actually revealed themselves and we recognized the layout of the field. The star was WAY too far away from the planet to be a part of the system. Once we dredged up the two brightest moons of the system, we spent the next 45 minutes or so attempting to get them to be viewed steadily with direct vision, a quest that was never met for an entire transit across the field of view. They were that challenging to see, and they're the brightest of the quint that can be seen by amateurs! And did I mention that we were wielding an 18" scope on the task? Child's play these are not!

So it was a good first attempt. We succeeded in seeing two moons of Uranus, something neither of us had done before. It's now clear that to be more successful, several conditions need to be met - a clearer sky, a darker sky, and a sky with better seeing has to be present. The remaining three targets are all dimmer than what we saw and closer to the planet as well. Believe it or not, even at mag6, the glare of planet itself will hide the dim moons when they're in close apparent proximity. Things have to be just right to see diminutive Miranda at mag15.8. Somehow I'm thinking it might be awhile before we bag that one! :lol:

My observing log from the evening:
UranMoLog.jpg
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After an observation I like to confirm my sightings with a planetarium program - in this case I used Stellarium:
UranMoons+Star.png
UranMoons+Star.png (58.96 KiB) Viewed 645 times
The magnitude of that star was bothering me. It was listed in Stellarium at 14.65, but it was seen by both of us before either of the moons. It didn't help when I went into CDC and it was listed at 15.12 with a UCAC4 designation - typically a reliable source:
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Untitled3.png (150.86 KiB) Viewed 645 times
Mike M.
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Pete
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Re: Viewing the moons of Uranus through the eyepiece.

Unread post by Pete » Tue Dec 03, 2019 9:11 am

Very nice Mike. Even at 6th magnitude, Uranus might be so bright as to warrant use of an occulting eyepiece when viewing its moons?
Pete P.
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Apollo XX
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Re: Viewing the moons of Uranus through the eyepiece.

Unread post by Apollo XX » Tue Dec 03, 2019 3:02 pm

That may help, Pete. Another consideration is to try looking for the inner moons when they're at their largest apparent distance from the planet. I always find it interesting in trying to find workarounds for the astronomical viewing challenge at hand. Sometimes we can come up with a gimmick, and other times all we can do is wait for the right conditions to present themselves. Either way, when we succeed it's a just reward.
Mike M.
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