Sinus Iridium Ejecta and Beyond

Lunar craters Mairan, Sharp, Harpalus and the Jura Mountains
Sketch and Details by Frank McCabe

The lunar feature known as the Jura Mountains includes the rim of the Sinus Iridium impact and is visible here in late day sunlight. The debris field can be seen extending westward to Mare Frigoris. All of Sinus Iridium is in shadow which gives this region an unfamiliar appearance. The impact that created the large mountainous debris field occurred during the Upper Imbrium period (3.8 billion years ago). Some of the mountains are a lofty 5 kilometers high. Superimposed on these mountains are two forty kilometer complex craters known as Mairan and Sharp; another similar sized crater can be seen on Mare Frigoris and is called Harpalus (39 km.). At high sun this crater shows a bright young crater ray system in addition to a fine glacis. There are 3 pillow-like features to the far left in the sketch at the edge of the Iridium ejecta. The two that are closest together are the famous large lunar domes known as Gruithuisen Gamma and Delta.
It is always worth while when not expecting a rigorous day ahead to get up a little earlier than usual to see what is going on in the sky before sunrise. This is especially true when the sky is clear and very transparent.

Sketching:

For this sketch I used: black Canson paper 9″x 12″, white and black Conte’
pastel pencils , and Conte’crayons, a blending stump, plastic and gum erasers. Brightness was decreased -2 using the scanner for this sketch
Telescope: 10 inch f/ 5.7 Dobsonian with 9mm (161x) eyepiece
Date: 11-12-2009 11:00-12:00 UT
Temperature: -3°C (27°F)
Clear to partly cloudy, calm
Seeing: Antoniadi III
Co longitude 212.7°
Lunation days 25.27
Illumination 20.1%

Frank McCabe