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Sunrise on Clavius
My 14-year-old son and I saw some spectacle last night. I pulled out
the trusty NexStar 5 for him to do a lunar drawing as part of the Boy Scout merit badge project. The sun was just rising on the floor of Clavius, so that the crater floor had a roughly centered pool of grazing sunlight interrupted by Clavius C and D. Each crater had a bright rampart and cast a long shadow, so the illuminated floor was outlined like two overlapping comet heads. The fact that the sunlight yet touched only the center of the crater floor was a graphic illustration of how strongly curved the luanr surface is. The whole of the inner walls of Clavius was still shadowed; part of the wall of Rutherfurd stuck into the darkness like a scimitar. Over 30-45 minutes, some new pieces of the wall of Clavius N and some smaller craterlets caught the sunlight. This overall appearance must not last more than a couple of hours - I've never seen it before. This is the phase at which I've convinced myself in twilight, before glare becomes a problem, that I could just catch a naked-eye hint of the notch in the terminator when Clavius' floor is in shadow. We also probed the limits of the NexStar's tracking in alt-az mode, since at this phase of the Saros cycle the Moon passes within 4 degrees of our zenith. Had to help out with the handset buttons for about 15 minutes. I grabbed a quick digital snapshot through the eyepiece as a memento, amd to accompany my quick sketch, but the NexStar short-term tracking wanders by arcseconds and has always limited the quality of images with a camera physically attached. Bill Keel |
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Sunrise on Clavius
On 26 Feb, 13:28, "William C. Keel" wrote:
My 14-year-old son and I saw some spectacle last night. The fact that the sunlight yet touched only the center of the crater floor was a graphic illustration of how strongly curved the luanr surface is. Well observed Bill, I had a similar demonstration at our last clear public night. What I initially took to be a star about to be occulted by the moon was in fact a central peak standing a hair off the northern limb ;-) I watched fascinated as it slowly dipped from view. jc |
#3
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Sunrise on Clavius
On Feb 26, 9:10 am, "John Carruthers"
wrote: On 26 Feb, 13:28, "William C. Keel" wrote: My 14-year-old son and I saw some spectacle last night. The fact that the sunlight yet touched only the center of the crater floor was a graphic illustration of how strongly curved the luanr surface is. Well done. Your son will never forget this observation and you won't either. Tonite's a good night to count the craters on the floor of Clavius. Well observed Bill, I had a similar demonstration at our last clear public night. What I initially took to be a star about to be occulted by the moon was in fact a central peak standing a hair off the northern limb ;-) I watched fascinated as it slowly dipped from view. jc I call those crater tops "floaters". They are more fun to observe than the craters themselves - really wierd looking. They can also be very useful in determining altitudes if one wants to do some hardball Trigonometry. Ben, 90.126 n 35.539 |
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