Wind and Nebulae at Fremont Peak

Observing at Fremont Peak, 1996 Dec 7

Saturday afternoon was overcast in the Bay Area, and star party prospects looked grim. Still, it looked like there might be a few patches of blue sky visible to the south, so, having heard that a few optimists were planning to be at Fremont Peak just in case the weather cleared up, and wanting a chance to field-test version beta 2 of the Dobsonian mount I've been building for my 6" f/8 Cave, I decided to give it a try.

About halfway there, it became clear (literally!) that this was the right decision, as the band of clouds ended abruptly just south of San Jose, and the skies were clear all the way to Fremont Peak.

As usual, I enjoyed the twisty road up to the Peak, at least up to the point where my car's engine suddenly lost power. I limped, sputtering, the rest of the way up the hill (if I'm gonna break down, I'd rather do it at the observing site where I can set up my 'scope and socialize with other astronomers while I work on the car :-), arrived at the top and discovered that the problem was only a loose plug wire. Whew!

Darkness fell, and the wind picked up. Planetary observing was difficult, since the gusty wind shook the telescope and made the air unsteady. (Beta 3 of my Dob mount will include more damping to keep the 'scope stable.) Galaxies weren't much better -- 7331 was faint and ragged in the 6" compared to previous views, and I couldn't find 891 at all. The bright white light coming from the vicinity of the radio towers (bright enough to cast obvious shadows) wasn't helping. Frustrated, I wandered over to the observatory for the 30" and spent some helping with an unsuccessful search for the Cartwheel galaxy.

A few sensible souls moved to a site farther down the hill, which turned out to be much better sheltered from the wind and the white light. Eventually the rest of us joined them, resulting in quite a collection of equipment set up there, including a JMI 18" (envious sigh ... what a beautiful piece of hardware!)

For some reason, although the wind continued to make galaxies difficult, the seeing was excellent for nebulae. I stumbled across the "tank tracks" (NGC 2024) northeast of zeta Orionis while sweeping aimlessly through Orion. Oddly, I found this nebula (both the bright portion and the dark lane) much easier to see without the UHC filter than with it. Isn't this an emission nebula -- shouldn't the UHC help it? I looked briefly for the Horsehead, but didn't try very hard, since my setup wasn't steady enough in the gusty wind to use high magnifications.

Someone commented on the surprising amount of nebulosity showing in the Pleiades. I had never been convinced that I had been able to see the Pleiades nebulosity (rather than dewing or reflections or some other explanation for halos around the stars), but this time, the Merope nebula was large, obvious, and clearly asymmetrical. I'm a believer now.

After viewing the Rosette nebula (NGC 2237-9 + 2244) in Monoceros through other people's instruments, I had to try it myself. In the 6" Cave, it was easily visible (even more so with the UHC filter), but too large to see much of it at once. Wanting to see more, I unpacked the 4.25" f/4 Coulter Newtonian, popped in a 25mm Plossl with UHC filter, and there was the whole Rosette, bright as day, a better view than I'd seen in any of the larger telescopes. I knew small RFT's were good for something.

"Thor's helmet", discussed recently on sci.astro.amateur, was faint and unimpressive in the 6", but was much improved by the UHC filter.

Meanwhile, a nearby observer discovered an interesting phenomenon. While viewing a nice open cluster with a bright foreground star (NGC 2362 and tau CMa) through a 14", he commented that when the wind jiggled the telescope, the foreground star appeared to move in a different direction from the cluster stars. This announcement, predictably, was greeted with jeers -- until the jeerers looked themselves, and discovered that everyone could see the effect. Most interesting! Presumably the effect has something to do with persistence of vision causing the perceived image of the bright star to remain in place longer than the perceived images of the much fainter cluster stars.

Alas, the clouds which had been lurking threateningly on the horizon for hours finally converged on the Peak, and it was time to head home.

... Akkana

Tau CMa was immediately dubbed "The Mexican Jumping Star".

When I went over to my 12" Meade LX200 to verify the location I noticed much to my surprise that the effect was absent using my scope. I tried several different eyepieces and methods of inducing field motion but in all cases the bean refused to jump. I'm guessing that the jumping effect is visible only if the star field appears to move rapidly with sufficient amplitude (the 14" Dob that we saw the effect with was wobbling horribly in the wind and felt a little springy when tapped; the LX200 was somewhat more stable (it was mounted in altaz mode)).

BTW, Burhnam's (p445) makes no mention of the Jumping effect but does have some interesting text about the cluster and the star. Apparently, the Mexican Jumping Star is a real brute with a mass of 50 to 300 solar masses and a luminosity 50,000 times our Sun's. The cluster is very young, even as open clusters go, about 1 million years.">Bill

Bill Arnett; last updated: 1996 Dec 9