Mare Angius

Mare Angius

Postby Aratus » Tue Jan 26, 2016 4:57 pm

Monday 25th January.

I took the opportunity of a brief window of observing the moon between it rising high enough at 2200, and the forecast of a front due to appear at 2300. The moon was waning 94%. Temp 8°C Wind 10mph NW.
Chocky the Cat escorted me to the observatory door, and then went off on patrol.
Two craters located near the terminator, Langrenus and Petavius stood out, but it was Mare Crisium which particularly caught my eye. Mare Crisium is normally oval looking in the N/S direction, but today it looked almost circular. This was due to favourable libration which placed that feature further into the lunar disk. The rays from the crater Proclus were noted to spill over into Mare Crisium. That is a feature best seen in a waning moon. Particularly interesting was a broad strip of shadow leading out of the mare in a north easterly direction. On closer inspection it was part of an ‘inverted T’ shaped plain just outside the boundary of Mare Crisium. Although I had reported the part of this which runs parallel to the edge of the mare, I don’t ever recall noticing the part of the plain now filled with shadow. None of my text books mention this feature, but the Times Atlas of the Moon records it as Mare Anguis. I had just enough time to take a photo before the cloud rolled in - earlier than forecast at 2230.
Chocky came running up wondering why I was going in so early. Having accompanied me inside, and being rewarded with cat treats, she went straight back outside probably lamenting my lack of adventure! For her activities - the night was still young!

On further investigation Mare Anguis ‘Dragon Sea’ was first named in the early 20th century and adopted by the IAU in 1935. There is more to it than I saw, but a lot of it is hidden behind craters and high ground. The ‘broad strip of shadow’ that I noticed seems to be where the mare cuts into the surrounding high ground. It is about 30 miles across.

The photo was a bit rushed and taken with a 0.63 focal reducer. My ‘broad strip of shadow’ is top left.
Image
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
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