A good opportunity to do more of this came on Friday evening, March 29 - Saturday morning, March 30. The Moon this night was almost three full days past Full and was due to rise around 11:00 PM EDT. What made this really interesting was that I had the chance to observe and photograph the Mare Crisium Sunset Ray (my own name for it) after midnight when the Moon rose high enough to be seen from my back yard. I hadn't seen this phenomenon for years; since it only happens for a few hours each lunar cycle. This "sunset ray" occurs when the mountains that surround the area of Mare Crisium cast a shadow over most of the plain itself, but one gap in those mountains, near the crater Tebbutt, lets the low sun keep shining through. This makes a long ray of sunlight visible on the Mare floor for several hours before the sun sets behind those mountains and Mare Crisium is in complete shadow. I've seen it a few times and sketched it, but never had the opportunity to try to photograph it.
The Moon was so low in the sky tonight, and there are so many trees to my south, that I only had a short window of time to look at it before it was blocked by the tree branches. It was a chilly night but not as cold as most of the nights have been. It was about 40 degrees F with light winds. I still bundled up in a winter coat. There were only small patches of snow here and there on the ground around me; the last leftovers from the late season winter storm that moved through our area six days ago.
I set the 10" f/4 telescope outside before midnight to let the optics cool down. The Moon was visible over the roof of a house to my south by 12:30 AM. I observed and photographed it for an hour between 12:45 AM - 1:45 AM. Unfortunately, the short window of time where the Mare Crisium Sunset Ray would have been visible was already past. The entire Mare was in shadow and only the lit-up mountains that surround this big flat lava plain were in sunlight. Still, I was able to get a lot of great looks at this and other features with my eye, and I was able to snap a lot of photos. Some of them turned out to be pretty clear, though I wouldn't call any of them spectacular.
My primitive method for imaging the Moon hasn't changed in the last couple of years, but I'm getting better at it. I use a cheap Nikon Coolpix digital camera held up to the eyepiece. This camera has a nice screen on the back, and as I hold the lens to the eyepiece I can usually get it in focus looking at the back screen. Then, as the Moon glides through the field of view of the eyepiece (since my telescope tracking hasn't worked for two years!) I just keep snapping photos every few seconds. When I'm done I download them to the computer and just sort through the displayed images, weeding out the awful ones from the clearer ones. (I haven't actually deleted any images yet, though, since one never knows if even a bad image might hold some good data!)
Here's an image of the whole Moon taken at 12:47 AM EDT March 30. It isn't a great image, but it gives a good idea of how the Moon phase was that night. The Moon was never higher than 25 degrees up in the Southeast sky, so it had a definite yellowish color to it when I was observing it, having to shine through the thicker atmosphere layers closer to the horizon. This was taken using 39X on the 10" telescope.
Here's an enlarged image of the limb of the Moon that was starting to go into shadow, so it shows the area of the Moon experiencing sunset. Mare Crisium is in almost complete shadow near the center at the bottom, but the mountains that ring it's western edge are still in sunlight. This photo turned out much better than I thought it would, showing a lot of detail. It was taken at 1:38 AM March 30.
Finally, here's a blow-up of the same photo as above, showing the edge of Mare Crisium in shadow and the mountain ring around one edge still illuminated by the sunlight. There was one prominent spot still lit up by the sun within Mare Crisium, and my best guess is that this was part of the edge of the crater Yerkes that lies on the floor of the Mare, but I could be wrong about this.
Besides just trying to take some "pretty photos" I did a lot of observing of the crater Aristarchus this night, and imaged it. This was as part of the Repeat Illumination Event Projects done by the ALPO (Association of Lunar and Planetary Observers) Lunar Section and by the TLP (Transient Lunar Phenomena) section of the British Astronomical Association. I'll cover the Aristarchus work done this night in a later post.
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