by Albert Highe
The forecasts, satellite maps, and CSC indicated clear skies for a few days at the beginning of the week. Clouds and rain dominated the forecasts for the remainder of the week. So I packed my 16" f/4.5 scope and headed to Michelle's Plettstone in the Sierra Foothills near Mariposa.
The skies were clear and the temperatures warm throughout most of the drive. In the East Bay, I noted a maximum temperature of 72°F! However, as I neared the foothills, the temperature dropped into the 50's and a milky haze lined the eastern horizon. That haze engulfed me as I climbed higher. It persisted all the way to Michelle's. I had never seen conditions like this at Plettstone before. It wasn't fog per se. Surrounding hills were visible, but uniformly veiled.
I expected the humidity to be high, but I set up the scope anyway. Sure enough, as soon as the sun set, everything became dripping wet. The sky was very dark, but bright stars were twinkling furiously and surrounded by halos visible with the unaided eye.
Oddly enough, by Midnight, conditions had improved. Moisture on the scope had completely dried up and stars overhead no longer sported halos. On the other hand, no stars were visible in the muck lining northern and southern horizons. I decided not to observe, hoping for better conditions the next night.
Tuesday, January 24, 2006
Conditions vastly improved the next day. Temperatures during the day were in the mid-60's. Skies were clear and views of surrounding hills were crisp. The air felt drier.
At sunset, the temperature dropped to the low 40's. Relative humidity was 55%. Everything was dry - a promising sign. Temperatures quickly dropped into the 30's by 6:30PM, but the humidity remained at a modest 77%. Despite the cold, I was comfortable. There was absolutely no wind.
The relative humidity reached a peak of 82% at 7:50PM with a temperature of 35°F. Seeing was OK, allowing magnification of 200X with the 9mm Nagler T6. Six stars in the Trapezium were easily visible. Skies were clear to the horizon. Oddly, the temperature increased and the relative humidity dropped over the next hour, reaching 40.5°F and 77%RH. The mechanism for these changes eludes me since there was no wind. After 9:30PM, temperatures resumed their downward trend, reaching 34°F (with 73% RH) by 1:30AM, when I stopped observing. At that time, seeing had deteriorated a bit.
Dry, clear, dark. As you might expect, it was a good night for hunting faint fuzzies. I logged approximately 60 observations - 35 of new, obscure galaxies spanning from Eridanus to Coma Berenices. The remaining observations were of bright favorites - planets, Messiers, and cruising Markarian's Chain.
I enjoy observing galaxy clusters and groups. One particularly tight group of five stood out. Members lie within a 10' circle and span the Leo - Virgo border.
NGC 3817 (13.3, 1.0' X 0.9')
NGC 3822 (13.1, 1.4' X 0.8')
NGC 3825 (13.0, 1.3' X 1.0')
NGC 3819 (13.8, 0.6' X 0.5')
NGC 3820 (14.5, 0.5' X 0.4')
The first three galaxies lie in Virgo and are nearly collinear with an orientation approximately WNW-ESE. The other two galaxies lie north of this line (just over the border into Leo) and are oriented approximately N-S. Apparent brightness, size, and shape (oval) of the first three are similar, although NGC 3825 appears more circular. All can be seen with direct vision, but appear somewhat larger with averted vision. Each has a very small slightly brighter core. The core of NGC 3825 appears to be stellar and the brightest among the three. The last pair are dimmer and smaller nearly-circular ovals. I could hold them steadily with averted vision. With direct vision, they almost disappear.
I also tried out a new piece of "observing" gear. My long-awaited power wheelchair finally arrived. In addition to motoring me around, it is equipped with a power seat elevator. The seat elevator replaces my adjustable observing chair. It was a treat to adjust the position and height of the chair with a push of a button.
Thanks again Michelle for allowing me to visit.
Posted on sf-bay-tac Jan 26, 2006 01:32:52 PT
Converted by report.pm 1.2 Mar 05, 2006 20:17:51 PT