by Matt Tarlach
Enjoyed some nice lunar viewing the last two nights with the ST80. Tried many combinations of eyepieces, barlows, and filters, before finally settling on 133x via 6mm UO ortho + 2x TV barlow, and a #15 yellow filter, for most of the viewing. Many lunar features were viewed over the two evenings; what follows are descriptions of those that appeared most interesting in the 80mm f5.
Last night, the stars of the show were the Straight Wall area and Plato. Throughout the session beginning at 0300 UT (3/14) the Straight Wall itself was prominent at all powers; Birt and Birt A stood out starkly. As I moved toward Rima Birt I started to run into the limitations of the little Short Tube. The dark area at the northern end was easy enough, and at 133x during steady moments I could make out Birt E within. The rille itself was much more elusive. For most of the evening seeing would rate Antoniadi III, but around 0430 UT there was a noticeably steadier interval. During this period at powers up to 190x the northern 2/3 of the rille was visible perhaps 50% of the time, and I had a few confident glimpses of the entire length.
The lunar terminator was passing over Plato during my session, and I spent much time there as well. As dawn broke across the floor of the flooded plain, the first beams of sunlight formed two delicate bands across the floor, looking for all the world like dark gray clouds. It was an oddly beautiful apparition, I think enhanced by the contrast with the bright rugged highlands surrounding Plato, and perhaps by the limited resolution of the ST80 which made the edges of the bright areas appear diffuse. As the southern band of light brightened and grew, I caught a glimpse of the small crater on the floor of Plato, just under the triangular land-slip on the southwestern wall. This small crater was clearly seen at powers from 133x to 190x for a few mintues, then as the angle of light grew higher it completely disappeared, not to be detected again despite repeated attempts. Later in the session when sunlight first touched them, the pair of craters just north of the center of Plato's floor was intermittently visible as a brighter aberration on the otherwise smooth dark plain, but never quite appeared craterlike nor resolved into two distinct objects.
Another feature noted in the region was a bright ray or scarp that appeared to reach out radially from near Plato's northern wall. It does not appear to be drawn in the Rukl Atlas, though it was plainly seen crossing diagonally across two ridge lines that are plotted there. The scarp (or ray) begins just west of the bright hill shown in Rukl at about 55 N, 8 W, and traces directly toward lunar North in an apparently straight line, extending just onto Mare Frigoris. It does not appear to radiate from Anaxagoras, which I believe is the center of a ray system; rather if it were to be extended it would pass quite to the East of that crater. When I returned to the region the next night it had completely disappeared; I suspect it is a scarp that is bright at sunrise and look forward to revisiting it around lunar sunset.
Tonight I spent most of my time in the area of Bullialdus, an interesting region that features samples of every type of lunar terrain I can think of. Bullialdus itself is a striking feature with a terraced interior, surrounded by a fair amount of ejecta. The flooded crater Kies was an attractive sight under the low lighting, and the large dome to its southwest quite easily seen in the ST80, though I could only detect a hint of the crater pit reported to occupy its summit. Bullialdus F appeared to be surrounded by a softly contoured, dark collar, appearing nearly dome-like and quite different from the commonplace crater drawn by Rukl. The most interesting feature seen here was a subtly contoured ridge reaching out more or less radially from Bullialdus toward the northwest. It appears to be the feature Rukl has indicated with a W-> symbol on his chart 53. As the Sun rises over the region, this ridge brightens along its entire length almost at once, then appears to gradually widen. It remains separated for at least two hours from the sunlit plain of Mare Nubium by a wide band of shadow stretching from Bullialdus toward Lubiniezky. At around 0430 UT (3/15) the small hill just north of Bullialdus L caught the sunlight, right at the head of this ridge. The appearance was for all the world like that of a comet, with bright nucleus and wedge-shaped tail, standing out from the still shadowed surroundings.