Morning at Crater Walther

Walther Crater
Sketch and Details by Frank McCabe

On this spring evening I drove over to our local community college to pick up and bring home the observatory telescope which was in need of cleaning and minor repairs. When I finished that work the sky was clear so I decided to use the scope to make a lunar sketch. The target I selected for drawing was the large (140 km.) Nectarian period walled plain crater Walther. On older lunar atlases this crater is either labeled Walter or Valtherus but in 1982 the name was changed to the current Walther by the IAU. I have always found the moon shows off some of its best large craters at this time in the lunation. Walther is one of those great old highland craters with much to offer a careful observer. Most seasoned lunar observers are well aware of the Walther sunset ray, but even at sunrise this crater has its rewards. A combination of craters with a common dark floor rests on the eastern rim three kilometers above the shadowed floor of Walther. To the west beyond the dark floor is the cratered, off-centered “central” mountain group casting a long triangular shadow across the resurfaced floor to crater Walter E (13 km.). Four small 4-6 km. craterlets can be seen in the drawing although at the eyepiece additional smaller ones were clearly visible in moments of steady seeing. To the northeast of Walther another large 3.9 billion year old crater Aliacensis (80 km.) was showing terraced walls and a central peak. The large younger Eratosthenian crater to the north of Walther is Werner (71 km.). Like the other two it has an off-centered central peak as well.

This was one of those observing nights when you wish time would stand still. I watched the long triangular shadow from Walther’s central peak shorten by 40% in just 2 hours.
I must say this was a beautiful night for moon viewing.

Sketching:

For this sketch I used: black Strathmore 400 Artagain paper, 9”x 12”, white and black Conte’pastel pencils and a blending stump. Brightness was slightly decreased (-2) and contrast increased (+2) after scanning using Microsoft Office Picture Manager.

Telescope: 13.1 inch f/ 6 Dobsonian and 6mm eyepiece 333x
Date: 5-13-2008 1:35 – 3:20 UT
Temperature: 7° C (45° F)
high clouds, calm
Seeing: Antoniadi III
Co-longitude: 4°
Lunation: 7.6 days
Illumination: 59.7 %
Phase: 78.8°
Observing Location: +41°37′ +87°47′

Frank McCabe