Observing Saturn

I never seem to have enough time to get out and observe, much less image, but since the Summer Star Party, I’ve been trying to get out at least once a week even if only for a short period. This usually involves sitting the Dob out in the back alley, then taking a long walk to get in a bit of exercise while I wait for things to cool off. Of course, living in Brooklyn, it’s really not until around midnight that the seeing starts to settle down. There’s just too much concrete and stone that have soaked up the heat during the day. And back during the 90+ heat waves, even waiting to midnight didn’t really result in good seeing.

But Monday night, I managed to get in a half-hour or so of sitting out and observing Saturday. Seeing was still mediocre and, of course, Saturn is not very high up, so it’s even worse since I end up looking over neighboring roof tops. Oh well. Still, it was good enough to warrant using the 6 mm Radian eyepiece. Occasionally, Saturn would snap into focus and the Cassini division would be obvious, along with a few pastel cloud bands. Titan was easily visible west of Saturn (left in the eyepiece view). Then I noticed a couple of faint “stars” near Saturn and will pop in and out of view with the seeing and had to wonder if I was looking at more of Saturn’s moons.

After checking with Sky Safari on my phone, I concluded that yes, I was definitely seeing two of Saturn’s moon as they locations were correct, Rhea (mag 10.3) near the 3 o’clock position (relative to Saturn’s rings in the eyepiece, which makes it east of Saturn) and Tethys (mag 10.9) near the 11:30 position (again, relative to Saturn’s rings in the eyepiece view). With Sky Safari as my guide, I tried but failed to pick out Dione (mag 11.1), and the fainter moons were also impossible.

I was a little surprised, and disappointed, that I couldn’t see at least Dione and I really did give it a try, tweaking the focus multiple times, letting the scope settle (sticky rack-and-pinion focusers result it a lot of shaking), waiting for the seeing to snap in, but I never did see it. From the math, I sort-of expected to see it. Typically, on a good night, I can see (naked eye) to magnitude 4 near the zenith. My test stars are in Lyra; if I can see zeta Lyrae at magnitude 4.3, it’s a good night. If I can’t see Sheliak (theta Lyrae) at magnitude 3.8, or I’m having trouble with it, it’s a bad night. This test is sensitive to atmospheric moisture and dust since here in New York City, there’s always lots of light pollution. I didn’t actually check Monday, but I don’t think it was a particularly bad night. The 200 mm aperture of my Dob should give me about 8 magnitudes improvement over my naked eyes (assuming my old eyes’ pupils dilate to 5 mm). So magnitude 12 should be within reach. But I definitely couldn’t spot Dione; maybe it wasn’t as good as I thought, or the combination of lower altitude and mediocre seeing were the problem. Still, it was fun to be able to spot those three moons.