2010 08 26, Geminus and Bernoulli

Phase: 342.4°
Lunation: 16.19d
Illumination: 97.6%
Lib. Lat: -5°48’
Lib. Long: -2°06’
Az: 206°48’, Alt: 46°49’

Geminus: complex crater, 56.7° E, 34.5°N
Eratosthenian Period (-3.2 billion yrs to –1.1 billion yrs)
Dimension: ~88×52 km, Height: 5400 km
Named after Geminus of Rhodes. Depending on which reference you use, he was said to have lived in 70 BC or in 50 AD (or thereabouts) and was a mathematician and astronomer.

Although this is a circular formation, it appears oblong because of an effect called foreshortening caused by its position near the limb. Even the central ridge appears offset from the midpoint of the crater floor. The moon filter helped bring out more details not only in the terraced walls of the crater but also the extensive ejecta and formations surrounding Geminus. An area of interest is northern rim of the crater. In the sketch, there are two bright circular areas representing notches that I first believed were craters. The rim itself appeared well-defined and very sharp.

Geminus C (16×16 km) is located just southeast of Geminus and Messala A (26×26 km) is located a little further to the northwest.

Here is a good photograph by François Emond on the LPOD site to support the foreshortening effect that I observed. Geminus, Foreshortening Effect

This is an image that shows what Geminus looks like from above taken by the LO-IV-191H. Geminus, Above View

Bernoulli: crater, 60.7° E, 45° N
Upper Imbrian period (-3.8 billion yrs to –3.2 billion yrs)
Dimension: ~49×49 km,  Height: 4000 km
Named after Jacques Bernoulli, 17th century Swiss mathematician and physicist

The central mountain in this crater was visible just outside of the encroaching shadow. The terraced southern rim appears to spill into the outer surroundings and the northern edge seemed to plateau connecting like a bridge to Bernoulli A.

Rukl plate 16
“The Modern Moon” by C. Wood pgs. 98-99
Geminus Gallery from LPOD
Virtual Moon Atlas

Paul was on a flight but the astro dogs kept me company. Even Nigel was wrapped around the base of my telescope mount next to my feet.

Buttercup, Freckles, and Riser

Freckles decided to do a little landscaping as I was putting equipment away and locking up the observatory.  She was certainly very pleased with herself.

Freckles caught in the act

Sketch completed scopeside on Rite in the Rain paper and charcoal.


~ by Erika Rix on August 29, 2010.

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