Mare Orientale, Finally

My previous post was about observing the the celestial western limb of our Moon with both favorable libration and illumination. I haven't been as lucky with the celestial eastern limb. Twice this year so far, in January and February, I've managed to observe Mare Orientale with favorable librations.

After waiting so long for a good phase and libration to see Mare Orientale, my chance came while I was at work the morning of January 16. This observation was during my 15 minute break, and I had to get out to my car, get out my telescope and set up, and try to get images as fast as I can. While my phone doesn't have much of a problem taking lunar pictures when the Moon is near full, it likes to overexpose the limb during the crescent phase. I had to combine my neutral density filter with my #80A blue filter, and turn down the exposure setting on my camera, just to try to compensate. It was cold, and the Moon was still low in the sky, with terrible seeing conditions. Saturn, though, was visible below the Moon, if you drew a line connecting the horns of the crescent, and followed it straight down.

In brief visual observing, I could see Lacus Veris, Lake of Spring, and beyond it, Mare Orientale on the limb. Being rushed, though, I didn't get any images worthy of posting if this weren't such a challenge just to get the necessary phase and libration. I'll let the photos tell the rest.

Then on February 13, we finished early at work, and were sent home at 3:00 AM. At first, I wasn't happy about it, but before I left work I remembered that it was a great morning to see Mare Orientale again, and the sky was clear. I couldn't wait to get home and observe.

Although I'd seen Mare Orientale in January, that was a very brief observation in the parking lot at work, with bad seeing conditions. This time the libration was even better for observing the Orientale region, and while seeing still wasn't very good, I had the time to wait, and it did improve a little as the morning progressed. Unfortunately, it was very cold, 1° F (-1° F wind chill) in Valparaiso, so I took several warm up breaks.

Visually, I was very pleased with the view, although I didn't manage to improve much upon my images from last month.

I was about to end the observation, but realized that I hadn't really observed much outside the Orientale region, so I scanned the lunar surface to see if anything interesting stood out. I then realized that there was something conspicuously absent. In the far south, near the terminator, I noticed a crater, later determined to be Casatus, that was surrounded by darkness, even on the day side of the terminator. I can't find much information about Casatus and surrounding craters other than size, but based on this observation, I have to think the region is in a basin deeper than the surrounding terrain.

Part of the eastern rim of crater Klaproth can be seen just above Casatus, but the northwest of Casatus is deep in shadow, even though it is on the day side of the terminator.

I love observing our Moon. No matter how well I think I know its surface, I always get surprised by something new, or seen in a new light, or in this case, a new lack of light.