Rille with a Hook

Rima Sirsalis
Sketch and Details by Peter Mayhew

Object Name: Rima Sirsalis
Object Type: Lunar Rille
Location: York, U.K.
Date: 31st October 2009
I used graphite pencil on white paper. My observing instrument was a
Skywatcher Skyliner 150mm f8 Dobsonian with a 10mm eyepiece and x2 Barlow.

Labeled sketch of Rima Sirsalis
Sketch and Details by Peter Mayhew

I have just endured twenty days of grey cloud without sight of the
stars: it was almost unbearable. This came with unseasonal mild weather
for October for the UK. On 31st, there was a brief gap in the clouds at
20:00 UT and I got the scope out to look at the day 13 moon; I spent a
few minutes deciding whether to sketch Wargentin or Rima Sirsalis, and
as you can see decided on the latter. High cloud rolled in but I kept on
going, and managed a passable sketch in decreasing visibility as the sky
turned foggy. The terrain which the rille cuts through is fascinating;
from the Ocean of storms in the north (bottom) past craters Sirsalis and
Cruger A, and then on reaching De Vico A it makes a westward hook
towards Lamarck and Byrgius before petering out. The nearby craters
Darwin and Cruger make excellent background scenery. I include a
labelled version. The rille is 420km long and 5km wide.