Invading Sol's Icy Moons

1997 September 5

I didn't have high hopes for doing any serious observing Friday night. But it had been so long since I'd been out (Montebello doesn't really count :-) that I went to Fremont Peak anyway. I figured that even if it was bright and partly cloudy that there were planets a plenty to take up the evening. I was not disappointed.

I began in the late afternoon by tring to find Mercury. It is a little WEST of the Sun these days so serious, sensible people look for it in the morning just before sunrise. But I though "what the heck, my LX200 can point to it; let's see what we can see." So with the usual sloppy alignment followed by synching up on Venus I had it pointing at the right place in the sky in a few minutes. But Mercury was not to be seen. The sky was just too bright. Mars and Jupiter were easy enough, though, even an hour before sunset. So were all the bright stars I looked for; it must be possible to see dozens.

Rod Norden showed up just before dark with his big 18" Obsession and a peculiar desire to see Neptune's big moon, Triton. Just for fun, I pointed my Meade LX200 at Neptune at aboud sunset. No dice, but what the heck, this is all for fun, right. So I left it tracking while I ate my dinner and before long the stars were popping out and sure enough there was Neptune right where it was supposed to be. As soon as it got really dark, I fired up my trusty Powerbook to see where Triton was supposed to be relative to Neptune. It was immediately obvious in Rod's 18" and visible, but much less easily, in my 12", too. The effect of the additional aperture was dramatic. Rod was very happy. At mag 13.6, Triton shouldn't be very hard but it is fun to be able to see such a small thing so far away (Triton is a little smaller than the Moon and it's 4.5 billion km away).

Like invading ETs flushed with success, Rod and I continued in toward Sol. Uranus has four moons that are possible with amateur scopes. Starry Night showed us where to look. Titania (mag 14.0) and Oberon (14.2) were pretty easy in Rod's 18". Ariel (14.4) was visible, too, with some effort. Umbriel (15.3) escaped my targeting scanners, but Rod claimed to see it intermitently.

Rod broke off the attack at this point, but I continued with the Saturn system. I had secretly prepared printed charts of Saturn's moons for the night. My real goal was Hyperion, the strange tumbling rock just outside Titan's orbit. At mag 14.2, I figured it would be easy after our success at Uranus. And so it was. Three of Saturn's icy moons were obvious at first glance, Titan, Rhea and Dione. Hyperion was right next to Titan and with a little effort fell to my averted gaze. Iapetus, whose magnitude varies from 10.2 to 11.9, was actually a bit more of a challenge since it was hiding among some nearby stars but my chart and a little "star hopping" unmasked it soon enough. Tethys popped out from behind Saturn a while later. Later still, Enceladus and tiny Mimas appeared, too, although they were right next to Saturn's disk and very difficult for me.

My conquest of the outer solar system is now complete. Counting Jupiter's Galilean moons (and Umbriel from Lassen), I have now seen every body in the outer solar system that I can reasonably expect to see. (There are a few more that observers like Jay and Akkana equiped with big scopes might attempt: Miranda and Phoebe are mag 16.5 and are far from their parents; Amalthea and Himalia might be possible, too, but Jupiter's brightness makes them tough.) Serious solar system invaders can track down numerous asteroids but they just don't strike my fancy. In the inner solar system, I'm still hoping to see Deimos and Phobos but that will have to wait until Mars's next opposition in 1999. Meanwhile, I guess I'll just have to hope for some more comets :-)

Bill Arnett; last updated: 1997 Sept 7