Monday, February 25, 2008

Planets offer pleasing views

Session name: 20080224.1900

A cold session with a light breeze chilled exposed cheeks and shook the scope. Early in the session clear skies yielded slowly to accumulating clouds entering from the west. Thin, semi-transparent sheets gathered beneath Orion and ultimately coated a large part of the sky by 10PM EST. Over the course of the observing session a half dozen passersby and dog walkers stopped for breathtaking views of Saturn. Charlie and Kin were absent as well as familiar dog owners.

Mars still reveals some features in the eyepiece despite its size at 9.4", much smaller than the 15.6" of 08 DEC '07. First, it is obviously a pinkish-red disk compared with the nearby stellar pinpricks. It has area and with a sprinkle of imagination one can sense volume. Secondly, surface features of different albedo and tone were apparent. A light breeze caused the disk to dance in the field of view, but with firm scope and steady seeing I could see clearly Chryse Planitia, a martian basin with a high albedo. This circular white area contrasted with darker marial regions to the north and south. The southern marial region was larger and broader across the disk than the northern one which appeared more localized above Chryse. I was unable to detect the northern polar cap which I had seen in previous sessions. Magnifications used 90x, 120X and 240x, finally settling on the 7mm's 120x magnification for a bright, crisp view of the diminutive red disk.

Saturn was splendid this session. Passersby remarked the same. If you plan to consider sidewalk astronomy, this is an ideal season because Saturn is sure to delight all that see him. I can't think of any other object in the night sky that thrills the pedestrian observer with disbelief and astonishment.

When the air calmed, the scope would settle long enough to drink in long views of the ringed planet and its satellites. I heard gasps from those who took a look in the eyepiece. At 120x magnification, one could easily appreciate Saturn's characteristic parts and shape. With more scrutiny during the calm moments, many features were observed.

On the disk of the planet, a salmon-pinkish toned belt ran parallel across the disk beneath (south) the ring. Of the ring system, Cassini Division on each side was a challenge but discernible. The A-ring offered a translucent glow which contrasted with the Division and whiter, opaque B-ring. Perhaps a shadow provides the darker lineal feature on the south side of the ring that crosses the planet. I am confused because tonight Saturn is at opposition and no shadows should be displayed. Like a full Moon, the Sun is shining directly on the planet from our point of view on Earth offering no shades of relie

Saturnian moons Titan, Rhea
, Tethys were clearly visible, pinpoints of light created by sunlight reflected off their surface. I suspected a prick of light inside Rhea's orbit but had wavering confidence. Checking planetarium software StarryNight at home, those pings of photons turned out to be Dione.
Lastly, I suspected a point of faint light about 5 Titan-Saturn-separations distant on the same side as Titan. Field notes agreed with the planetarium program indicating this unusal moon at magnitude 10.92. There is not much room for the limiting magnitude in this scope under these skies. (Magnitude 11.6 with previous measurements using NGC225 and NGC1647.)

I finished of this session with a practice run for GAN'08. I was able to detect stars as faint as 4.7 above Times Square. I don't propose that NYC has dark skies but that my observation skills, visual acuity, and confidence allow me to see pinpoints of light, even if more contrats is desired.

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