Astronomy Sketch of the Day

Bullialdus and A and B
Sketch and details by Richard Handy

Sitting in replendent isolation on the lava plains of Mare Nubium, the magnificent 61 km Bullialdus reflects the early morning sunlight strongly off the steep cliffs ringing it’s western rim. If you were to stand on this precipice next to this face, a nervous downward gaze would reveal huge islands of collapsed rubble nearly 1800 meters of almost vertical drop below you. Wrapping around in great arcs with your field of view, on the opposite side of the crater, these giant terraces would appear as tumbled foothills rising from a deep gray plain, interrupted by the brightly lit jutting central peaks of Bullialdus. The wreath of folded crust that forms the glacis of Bullialdus is one of it’s most alluring aspects. It seems replete with craggy flows of broken crustal rock arranged radially around the outer rim. As an Eratosthenian aged crater, little is preserved of this iconic crater’s once prominent ray system, but at one time it must have been quite a sight, powdery rays splayed across the long cooled Nubium flows. But time, sunlight and micrometeorites fade everything. Craters like Bullialdus are classified as complex craters. The force of the impact of the original asteriod is strong enough to distort the surface downward a few kilometers. In response to this compression, the surface rebounds almost explosively, creating extraordinay results: central peaks and rim terrace mega collapse slides. Bullialdus’s peaks are close to 1000m high. The annulus of mass wasting, especially in a couple of areas to the south west of the floor do appear to almost encroach on the central peaks. To the south of Bullialdus is Bullialdus A. There seems to be a scooped depression that connects Bullialdus to it’s diminutive neighbor, as if the shock of A’s formation created a landslide off this section of the glacis of Bullialdus. Futher to the southwest Bullialdus B echos this odd terrain.

Sketch Details:

Date: 6-25-07 Start- 4:30 UT End- 6:00 UT
or: 6-24-07 21:30 to 23:00
Lunation: 10.05 days Phase: 61.1 deg Illumination: 74.2%
Lib. in Lat.= +5 deg 56 min Lib. in Long.= -00 deg 10 min
Seiing: Antoniadi II to III Weather: clear
Telescope: 12″ SCT f/10
Bino viewer: W.O. Bino-P with 1.6X nosepiece
Eyepieces: 12.4 mm Meade Super Plossls
Magnification: 393X
Medium: White and black Conte’ Crayon on textured black Strathmore paper.
Sketch size: 18″x 24″

Schluter, Grimaldi, and Riccioli Craters
Sketch and Details by Frank McCabe

At one day before full moon the illumination along the western terminator, nearly at the limb was highlighting the Upper-Imbrium crater Schluter (92 km.) with its central peak protruding out from the darkness of the crater floor. The outer reaches of Mare Orientale in the name of the Cordillera mountains were just beyond the sunlight at the lunar limb. The largest feature in this sketch is the lava covered, very dark floored impact basin known as Grimaldi (230 km.) What we see of Grimaldi is the inner ring of a 440 kilometer, two ringed mini-basin. This Pre-Nectarian impact event was originally described as a walled plain crater of advanced age with a heavily worn and battered rim. The basin is noted for a large gravitation anomaly beneath the surface associated with a high mass density concentration. Adjacent to Grimaldi to the west is semi-dark floored walled plain crater Riccioli (150 km.) At the same age as its eastern partner it shows damage and age especially from the ejecta pitched out by the Mare Orientale event.

Sketching:

For this sketch I used: black Strathmore 400 Artagain paper 9”x12”, white and black Conte’ pastel pencils and a blending stump. After scanning, Brightness was decreased (-5) and contrast increased (+4) using Microsoft Office Picture Manager.

Telescope: 10 inch f/ 5.7 Dobsonian and 9 mm eyepiece 161 x
Date: 8-16-2008, 3:15-4:40 UT
Temperature: 15° C (59° F)
Clear, calm
Seeing: Antoniadi III
Colongitude 85.7 °
Lunation 14.7 days
Illumination 99.4 %

Frank McCabe