2011 10 07, 0330UT Eratosthenes
PCW Memorial Observatory, OH, USA, Erika Rix
www.pcwobservatory.com
Eratosthenes: Complex crater from Eratosthenian geological period (from –3.2 billion year to –1.1 billion years)
Lat: 14.5 deg N, Long: 11.3 deg W
Zhumell 16”, 21-7mm Zhumell, 257x, no filter
Temp14C, 89% increasing to 98% humidity, S: Antoniadi II, T: 6/6
Eyepiece sketch on Rite in the Rain paper, charcoal
Phase: 54.3 deg, Lunation: 9.68d, Illumination: 79.1%
Lib. Lat: -05:01, Lib. Long: +05:37
Az: +246:38, Alt: -07:34
Eratosthenian geological period includes fairly young, non-rayed fresh craters. I did notice a Copernican ray to the N of Eratosthenes and several patches of lightened areas within the surrounding areas. Eratosthenes has very steep, tormented walls and is approximately 60km x 60km wide. It has an elongated central mountain with several summits. Its morphology is very similar to impact crater Copernicus, but its rays most likely deteriorated from weather and age.
The distance of this crater from the terminator made it perfect for studying the floor and terraced walls. The western floor edge was difficult to differentiate from where the upslope began for its wall. It appeared to be more a lightening with a few darkened lines.
For comparison, here is an image from the Lunar Orbiter (through the Lunar and Planetary Institute site). My sketch is the eyepiece view from my telescope and will need to be rotated 180 degrees to match the Lunar Orbiter image.