Greetings, Mars fans! ;-)
Well, tonite I had a decent opportunity to try my newly fabricated occultation cell. This thing works very well. The bar in my 25mm TV Plossl takes up about 20-25% of the FOV; in my 20mm TV Plossl this would be closer to 30%. Anyway, it's the right balance of size to occult Mars whilst still allowing some planetary observing for fine focus. Just excellent. The flat black I used really was dark. The edge is razor sharp, like that of a well-made field stop. Nice. Having a helical focus ability to fine tune the edge sharpness really works well. Not all field stops are exactly in the same position. I can adjust this over a 5-6mm range, if necessary, but only require around ~1-2mm range for the TV Plossls I use.
I used the Sv102D [aperture!] and my 5x Powermate, with the 25mm TV Plossl for 141x. I wanted enough image scale to allow me to see something, but not to overdo the magnification so as to dim the moon. I also wanted my sky really black, or as dark as was possbile. I might have had an easier time doing this at slightly lower power, say ~100x. I will have to try that another night.
Seeing was around a 7/10. Transparency was crap at first - Mars was buried in heavy haze and hardly visible. I almost did not go out, but then saw the haze lifting to the SE. Out I went. I mainly wanted to try the thing to evaluate it's performance, but I did not expect to see Phobos, actually. Transparency went up to 8/10 for about 20 minutes. During this time, I thought I saw something at the 8-o'clock position leading Mars. HD216809, a dim 8.4 magnitude star was conveniently in the FOV and could be used as a "magnitude guage" of sorts [lucky!]. I was not fully happy with the situation, and in preparation of this, brought my Baader Contrast Booster [BCB] filter with me to try out in this situation. My 5x Powermate is front-threaded for filters. Since I have a non-threaded cell in front of the occultation cell, I had to use the threads on the 5x PM...
The BCB did a very decent job of enhancing MArs detail over the unfiltered view, though it was still inferior to the 3M filter [3M = "Magic Mars Magenta" filter] I now prefer. Still, even at 141x, the SPC, Hellas, and some Maria were discernable, including some extensions of Sinii near the prime meridian. To be honest, I did not wish to get lost in looking too much for Martian details, 'cause that's what blew my last opportunity!
Okay - using HD216809 as a guage, the BCB filter immediately darkened the background sufficiently to make it stand out noticably better than without it in. I KNEW that I'd find a really good use for this puppy! Call it "filter" instinct. During the 20-25 minute window, I adjusted the bar's orientation to be as perpendicular to the SPC as practical. I then allowed the planet to track across the FOV, and once it hit the bar and dissappeared, I verbally timed it. I repeated thsi procedure, looking towards the leading side of the planet as it was tracking [westward] across the FOV. Remember, I'm using an alt-az mount. At around 0810 UT, my first hint of what might be the moon occurred. It was around the 8-o'clock position [approx.], and I continued the session, looking carefully in the area ahead of the disk where the moon should approximately be. It was close to the visual threshold, so I wanted to be sure. I slightly re-oriented the occulting bar to give a bit longer time delay for the reappearance of Mars. About 0814 UT, I saw the object again - about one Mars diameter away, still in the same positon relative to Mars as I saw before. After another 5 minutes, thsi object was seen again. 3 times lucky, right?
The seeing dropped within 5 minutes of the last sighting to around 6/10, plus a breeze was getting stronger - I packed it in. I verified everything AFTER coming in, both with S&T's Martian Moon Java applet, and my Skychart III program [where I identified the star sharing the FOV].
I am pretty certain that what I saw, right near the visual threshold for the conditions tonite was Phobos. Nothing else was there, and the sky was suffienctly darkened using the BCB to allow the likelihood of this observation. I also employed an observing hood to minimize ambient specular reflections off my eye from distant light sources. I also used the diagonal baffle, and the occulting cell I made has one built in, to further reduce scatter/maximize contrast. So, that's seven baffles, altogether, in the train. If that ain't gonna do it... ;-) I also saw the object three separate times in the same orientation and relative distance to Mars.
If it wasn't Phobos, then I don't know what it was! If there was no slight haze at all, I'm certain that Phobos would have popped into view more noticably, because the combination of the high contrast inherent in the 102D's design, plus my careful construction of the occulting cell to include an integral baffle, use of an addiitonal diagonal baffle, bar darkening, medium high power, etc... the sky was really black. Further, Mars had no major ambient "glow" or any halos about it, except for perhaps a VERY slight glow right as the disk was passing the occuting bar's edge, re-entering the unobstructed area of the FOV.
I'll leave it to you folks - did I see Phobos? Anyone else had any success?
You DSO nuts are gonna flip trying this one out! ;-)
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