The San Francisco Bay area observing group, "TAC" (The Astronomy Connection) held a public star party on the grounds of Fisher Middle School, in Los Gatos, California, on the evening of Friday, April 11. Members brought more than 20 telescopes and binoculars. Public attendance was lighter than we had feared -- perhaps comet fever is wearing off.
The school is in a suburb near the southern limit of the contiguous urban area surrounding San Jose. It is an in-town site, but about as dark as one can get within the built-up area of a suburb. The Bay Area sometimes has excellent seeing, too. On this night, though conditions were jittery just after sunset, a few hours later, my Vixen 90 mm fluorite refractor was running diffraction-limited, with steady Airy disc and rings.
I spent the early part of the evening with the Vixen pointed at suitable objects for public viewing, which I looked at myself when no one was in line. This small refractor is nice for public work. It is not as intimidating as some larger telescopes, at least, not unless I tell people how much it costs.
I bought the 90 mm together with a driven Great Polaris mounting in 1989, used, for $1200 -- it would be a lot more at today's exchange rates, if Celestron were still importing them. On being advised of this price, one eight-year-old astronomer wannabe did the relevant calculation in a flash, and promptly replied, "Gee, that's sixteen years' allowance!" I sympathized, I've been an eight-year-old astronomer wannabe myself. Another family had bought a 50 mm Meade for their youngster -- I suspect it was a model 165, from their description. Both father and son claimed that they couldn't see anything but the Moon through it; I tried to point out that with practice and development of skill, there was quite a lot more that one could do with even such a small instrument. One can -- I have a newbie friend who is an enthusastic observer, who has almost completed a Messier survey with a Jason 50 mm.
In any case, the Vixen 90 looks small enough that many beginners can imagine having one like it. The sidereal drive means that I am not forever having to readjust the position. The long eye-relief eyepiece I was using -- a Vixen Lanthanum 6 mm -- meant not only that newcomers could find the right eye position easily, but also that they could leave glasses on while observing which meant that I could set the focus once, and leave it.
Comet Hale-Bopp was putting on its usual good show -- three arcs of the lawn-sprinkler were easy. The Moon provided some dramatic views. Rupes Cauchy and nearby Rima Cauchy I protruded from the terminator. The tapering shadow from the former looked like a fancy brush-stroke done in black ink. This formation resembles the better-known Straight Wall in its appearance at sunrise and sunset. To the north, G. Bond I was similarly prominent. The Vixen was showing all the detail in Rukl's atlas for these objects, and perhaps a little more. A nearby Astro-Physics (AP) 180, at exactly twice the aperture, was also pointed at the Cauchy area, and gave a spectacular view.
Not all passers-by had luck with fine detail. For them, I pointed out Mare Crisium, and we discussed whether it more nearly resembled the face of a teddy bear or that of a hedgehog. The teddy usually won, I suspect on grounds of cuteness.
Orion was settling toward the hills in the west, but I decided to try the Trapezium anyway, and was rewarded with six stars -- I could hold E pretty steady, but F kept popping in and out. This was early in the evening, before the seeing had settled completely, but by the time it had, Orion was too low to try again.
The prize of the night was Mars. I had looked at it early on, and seen the north polar cap, the dark rim around it, and hints of shadowy detail, all in so-so seeing. Later, I was wandering around, and the AP 180 was doing a fine job at 324x. There was enough detail that I was prompted to go fetch my atlas and try to identify some of it. The longitude of the central meridian was roughly 185 degrees. Sure enough, the dark areas Mare Cimmerium and Mare Sirenum were visible to the south, the dark streak of Cerberus lay diagonally across the planet, that broad white area north and west (Arieographic directions) of it was Elysium, and the little white spot not far from disappearing around the eastern limb must be -- holy cow, it's Nix Olympica!
For all the laughing one may do at some of the early Mars maps drawn with Earth-based telescopes, the classic cartographers of the Red Planet had one stroke of luck with names, in associating the snows of Mount Olympus (aka Olympus Mons) with the clouds and frost that form on the slopes and top of a Volcano some 25 Km high. There is not too much doubt that that is what we were seeing -- the spot was very white and quite round -- a little too regular for a detached cloud. The position was right, to as close as I would care to call things on the Martian disc (probably not better than fifteen degrees of arc on the surface), the size was right, and there isn't much else on the chart that it could be. What fun! There aren't many features on Mars, visible from Earth-based telescopes, that truly reflect topography, and this is one of them.
It was time to try some other telescopes. A nearby observer with a 12-inch LX200 slewed it to Mars. At 380x, the view showed about as much detail, maybe even a tad more, but at markedly reduced contrast. The 12-inch was feeling the seeing more than the AP 180, and I think also had a slight collimation problem.
How about the Vixen 90? Seeing had settled since my first view, so that a lot more detail was visible at 135x, but I was unwilling to call Nix Olympica any more than "suspected" at that magnification. The view was as contrasty as the AP 180, more so than the 12-inch, but showed less detail than either of them. Well, how about more magnification? I dropped in a 4 mm eyepiece, and sure enough, both I and several other observers were able to see the tell-tail white spot. Whee! Martian topography at 100 million Km, in an aperture most people associate for the most part with beginners' telescopes. The result is doubly interesting, in that at more favorable oppositions, Mars gets almost twice as close as on this night. Therefore, Nix Olympica might be visible in a good 50 mm refractor at the next close opposition. Perhaps the young man with the Meade 50 mm will have learned how to use it at the limit of its capability by then.