Lunar Craters Atlas and Hercules
By Frank McCabe
Atlas and Hercules the well known crater pair in the northeastern corner of the moon
are not far to the southwest of Endymion. Atlas (87 km.) the largest of the
pair may also be the younger of the two although it is listed as Upper Imbrium
era. Hercules (69 km.) is considered to be Eratosthenian in formation and thus
both craters are older than three billion years. Based on a lower crater
(craterlet) count and the younger appearance of the glacis, the Hercules impactor
may have struck first, followed by a few small crater forming strikes and then the
Atlas forming impact. The floors of these two craters are quite different from
each other. Atlas has a floor the is centrally uplifted and fractured into deep
fissures and rilles (Rimae Atlas) from the uplifting magma below that was unable
to flood the floor in the way that occurred with Hercules. The floor of Hercules
is mostly flooded with dark lava and contains a 13 kilometer crater (G) near its
center. The hotel sized rock that struck here less than a billion years ago left a
bright crater with rays that can be seen at high sun. A ghostly crater designated
Atlas E (58 km.) was justvisible north of Atlas and smaller Keldysh (34 km.) to the
north of Atlas E
Sketching:
For this sketch I used: black Strathmore 400 Artagain paper, 9”x 12”, white and
black Conte’pastel pencils and a blending stump. Brightness was slightly decreased
(-8) and contrast increased (+8) after scanning using Microsoft Office Picture
Manager.
Telescope: 10 inch f/5.7 Dobsonian and 6mm eyepiece 241x
Date: 2-14-2008 2:10-4:15 UT (actual sketching time was 50min.)
Temperature: -7°C (20°F)
partly cloudy, calm
Seeing: Antoniadi III
Co longitude: 358.6°
Lunation: 6.9 days
Illumination: 48.6 %
Phase: 91.6°
Frank McCabe