As the evening progressed the sky became mostly clear with some ground fog adding to the light scatter and the inevitable falling temperatures of an early spring night. Nevertheless, it was good enough for some observing and sketching. Crater Theophilus (100km.) was more than 450 kilometers from the terminator but remained an attractive target in the eyepiece as the Moon cleared a nearby building in my southeast.
Theophilus is a complex Erastothenian era crater at just over 1.3 billion years in age with large central peaks of deep crustal material that formed on the rebound from the initial impact. The appearance looks fresh when compared to its much older Nectarian period neighbor Cyrillus (100 km.). It was evident while observing this pair that Cyrillus was showered with ejecta from Theophilus and prior millennia of countless strikes by incoming rocks from space. The central peaks of Cyrillus are smaller, more muted and worn down. 300 kilometers to the west of Theophilus the Apollo 16 astronauts Charles Duke and John Young collected 96 kilograms of rocks over 3 days back in 1972 which included some ejecta from the Theophilus formation.
Remote sensors on the orbital spacecraft Chandrayaan-1 detected Iron rich Magnesium –Aluminum oxides on the central peaks of Theophilus adding to the knowledge of the composition to the deep lunar crust as indicated by a publication last spring.
Two other craters included in the sketch are Mädler (29 km.) also of Erastothenian age and Ibn-Rushd (34 km.) an ancient one at more than 3.2 billion years.
For this sketch I used: black Strathmore 400 Artagain paper 8″ x 10″, white and black Conte’ pastel pencils, a blending stump, white Pearl eraser. Contrast was slightly increased after scanning.
Telescope: 10 inch f/ 5.7 Dobsonian and 6 mm eyepiece 241X
Date: 3-30-2013; 04:30-05:35 UT
Temperature: 2° C (36° F)
Some thin clouds, calm
Seeing: Antoniadi IV poor
Colongitude 128.9 °
Lunation 18.4 days
Illumination 90.1 %