An Early Morning with Sinus Iridum

Sinus Iridum
Sinus Iridum
Sketch and Details by Frank McCabe

In the waning moonlight the shadows of the Jura mountain peaks could be seen on the floor of Sinus Iridum. On this mid-August night I was experiencing and enjoying a full night observing and sketching. The moon occupied my time during the second half of this session all the way to sunrise. It was one of the rare nights with cool dry air and great seeing conditions.
Sinus Iridum (260km.) is what remains of the Upper Imbrium impact on the floor of the Sea of Showers. The dark basaltic lava floor with its wrinkled ridges could be clearly seen as the sunset shadow was approaching. Several notable and recognizable features could be seen and included Promontorium Heraclides at the southwestern end of the crater rim arc over to Promontorium Laplace on the northeastern side. Old craters Mairan (40 km.), Sharp (40 km.), Bianchini (38 km.), were all clearly seen and sketched as well as the younger impact scars of Harpalus (39 km.) and Bauguer (22 km.), with ancient Mare Frigoris (Lower Imbrium) beyond the remains of the ejecta of Sinus Iridum. Much of dorsum Zirkel (216 km.) and dorsum Heim (134 km.) could be seen paralleling the terminator at the lower end of the sketch.
I was pleased I did not miss this fine evening for observing and sketching at the telescope.


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: 8-15-2009 10:00-11:20 UT
Temperature: 16ยฐC (60ยฐF)
Clear , calm
Seeing: Antoniadi II
Co longitude 206.3ยฐ
Lunation days 24.3
Illumination 32.1%

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