Petavius

[Mike JW]

A two hour clear spell gave me a chance to scan the lunar surface just 24 hrs after full moon. There were so many wondrous sights. I chose Petavius. Its Rille was a bright white line, the terraced walls were just awesome, the valley to the south was half in shadow - so black and jagged. I spent an hour doing rough sketches, checking an online image, making notes.

This morning it has been raining hard so below is the result of my efforts, sketching and reading up.

 

Along with Vendelinus and Langrenus these three large craters are easy to see but need good seeing  and correct illumination to pick up detail otherwise Rima Petavius is hard to spot. Petavius belongs to the small group of craters that have been modified post formation. In this case what caused the fractures? (Rima P. is the biggest but there are other much smaller ones.) Volcanism is the likely cause but there is very little dark pyroclastic material in the crater. However the central floor is domed shaped suggesting basalt lava rose up but not much escaped to smooth out the floor. The floor is 300 metres higher in the middle compared to the sides. The rising floor split the central peak (1.7km high). The walls are terraced (two major terraces and I suspect several smaller ones) and at its highest are 3400m above the crater floor. The crater walls are unusually wide in proportion to its diameter. The crater is circular but as it sits near the lunar limb foreshortening gives it the oval appearance.

Crater Wrottesley has clobbered the crater rim on the NE side and judging by the shadow the wall furthest from P. is the steeper wall.

Last night reminded me why lunar observing with sketching, followed by spending the time writing up/reading is so worthwhile.

Mike