Dave Wallace's Adventures in Astronomy

11/23/2003 0030 UTC

Tonight, for the first time, I was able to set up at the ATMOB club house site. It was very nice having truly dark sky to play in, though it took several trips from my car to the corner of the field to tote the gear. (There are advantages to using parking lots, I guess.)

Since it was my first time at this site, I decided that in addition to setting up the telescope, I'd set up the camera on another tripod and try photographing star trails. So there was a bit more gear to set up than usual and I was doing all the set-up in very dark conditions. But I had everything set up and operating by 7:45.

The two-star ("easy") alignment wanted to use Capella as one of the targets. Unfortunately, it was out of sight because I was situated behind the club house, which put the camera where other club members coming and going from the parking area would not shine light on it. But it meant that my view to the east was somewhat obstructed. As a consequence, I just hit ENTER when the scope finished slewing. The second target was Vega, which I could see. I zeroed in on it and hit ENTER. The Autostar liked the result, but I knew the targeting would be off. I decided I could live with the error if I stayed within a few degrees of Vega while waiting for Capella to clear the house, then I'd re-do the alignment later.

So I started off playing around in the Lyra and Cygnus area, since those constellations were still well above the trees. Hit the usual suspects -- epsilon Lyra and Albireo. Tried again for the Ring Nebula. No luck. Either I need to spend a lot of time star hopping in Lyra until I'm sure the GOTO has brought me to the right place or it's just not possible to see this object in a 90mm telescope and I'll need to try to capture it photographically.

Around 8:15, I decided to try for another look at Mars. The goto was way off, but Mars is an easy target to center on, so I got the scope corrected in short order. Nothing much to see even at 83X. I tried the moon filter and all that did was improve the color -- the planet went from off-white to pale orange as I dimmed down. Any detail revealed by this was probably more in the observer's imagination than in the eyepiece.

So I pulled the moon filter and re-targeted at Uranus. Got it in one, almost in the center of the field. No detail, of course, but a pretty shade of turquoise.

Around 8:45 I set the telescope on the Pleiades, hoping to see even more stars in that cluster from the darker skies. Sure enough, I was seeing maybe twenty more stars than I would have from Roberts Field or from my driveway.

By 9:30, three star trails shots had been taken: exposures of ISO 100 at f/8 for 5, 30 and 60 minutes. The five-minute exposure had a black background (as I would have expected); the 15 minute exposure was not black -- more like a dark brown; the 60 minute exposure was even brighter, though it still had good contrast. If I try this again (and I probably will), I'll know to stop down another stop or two; it shouldn't make much of a difference in terms of the number of trails (Polaris was significantly burned in all shots at f/8), but it will make the background darker for any given time. Anyway, with a little PhotoShop trickery, I was able to darken the background. So here's my first effort at capturing star trails on purpose:

Star Trails

As you can see, the framing was a bit off-center. This was partially to avoid a beacon light on a tower and partially because I couldn't see exactly where in the viewfinder Polaris had wound up. (The reddish color of the background before processing might have been due to diffuse light from the aircraft beacon.) Next time, I'll also try a wider angle lens: I was using a 50mm lens on my Digital Rebel -- that has a field fo view about like an 80mm lens on a 35mm film camera. If I can dodge the beacon, I'd like to get more of the sky in the frame.

One other noteworthy observation about the star trails photo: notice how the trails suddenly get about a stop dimmer around 40 minutes into the exposure? This correlates with a sudden change in the sky transparency that happened between 8:30 and 8:45 -- the other observers started complaining that the sky had turned "muddy" all of a sudden. Maybe a star trail exposure is a worthwhile diagnostic tool to record changes in the observing conditions.

By now, Orion had gotten high enough to mostly clear the roof of the club house, so I decided to try for M42. I used Rigel as an intermediate target, got the computer to lock on it and then asked to goto M42. That worked fine -- I had the Orion Nebula in the field on first try. A little touch-up and it was centered in the 26mm eyepiece (48X). This was my first view of this object since an early-evening session last spring. The view at 48X wasn't significantly different than from Roberts Field. But with the 40mm eyepiece (31X), there was a lot better contrast. And with the 15mm eyepiece (83X), I could easily spot the four brightest stars in the Trapezium.

By 10 PM, Saturn had cleared the roof of the club house. A few minutes fiddling got it centered. At 83x, I had a pretty nice-sized object, but it looked like I was seeing it from the bottom of a not very still pond! I guess the atmosphere wasn't too stable. Or maybe it was just the air above the club house roof. Anyway, the Cassini division was not visible. Titan was easy to spot and I might have also seen Rhea -- both moons were pretty far from the planet (on opposite sides) and both were surely bright enough to be seen under the conditions obtaining at the time.

The breeze suddenly picked up around 10:15. Since the temperature at the time was already a few degrees below freezing, I decided it was time to call it a night -- my hands were getting quite cold even with gloves on. All in all, an excellent night even if Rhea was the only new object I found.