I've gotten involved over the last few months with the Repeat Illumination Event Program run jointly by the Association of Lunar and Planetary Observers (ALPO) and the Lunar Section of the British Astronomical Association. This program is coordinated by Dr. Tony Cook in the U.K.The goal of this program is to observe and also sketch or photograph features on the Moon that have been the sites of TLP (Transient Lunar Phenomena) reports in the past, when these sites are under the same illumination and libration conditions as they were when the reports were made. That way, if the area shows a color change, an unexplained bright area, or an apparent obscuration, then there's evidence that this isn't just a random event since it would have appeared that way more than once at the same sun angle.
The Aristarchus area is the place on the Moon where the most TLP has been reported. Observers have supposedly seen brightness changes (it's the brightest crater on the Moon anyway) and sometimes red, blue, or other colors within and around it. The nearby crater Herodotus has also been the site of some of these rare reports. Though it has a smooth floor (and this has been proven on photos taken by spacecraft orbiting the Moon), there are rare instances where experienced observers have seen what looks like a bright central peak in it. Some thing this could have been caused by a temporary cloud of dust catching the sunlight, raised by an out gassing event. There have also been clouds and color changes reported in a nearby wide area of Vallis Schroteri (Schroter's Valley) called the "Cobra's Head."
The location of Aristarchus / Herodotus is shown on the photo of the Moon below (a photo I took on March 30) using a red square.
The photograph below is one I actually took earlier this year on the morning of February 24. This shows the Aristarchus area under better lightning conditions than it had on March 30, but I wanted to throw in some labels showing the major feature. (South us up in these photos, since this is how it appears through the telescope eyepiece.)
On the morning of March 30 between 5:27 - 6:27 UT (1:27 - 2:27 AM Eastern Daylight Time) this area was under repeat illumination conditions of a TLP observed on August 26, 1964 by Gennatt. The report on file for that event almost 49 years ago reads like this:
Aristarchus 1964 Aug. 26 UT 02:00 - 03:00 Observed by Gennatt, Reid (Greenbelt MD 16" reflector, x360, S=P-G) and Lindenblad (Washington DC, USA, 26" refractor) "Red and Blue bands. Grew thinner & shorter. Alerted Naval Obs. One obs. tho't he saw Phenom. but not sure. (confirmation?) (prof. astronomers, but not lunar observers)" NASA catalog weight = 5 (very high). NASA catalog ID #844
I spent about 20 minutes gazing at Aristarchus under high power between 1:25 AM - 1:45 AM (5:25 - 5:45 UT) on March 30. The Seeing was about a 7 out of 10; there were actually long moments of steady viewing with occasional atmospheric "rippling" which was good considering the Moon was never more than 25 degrees high in the South-Southeast sky. The Transparency was only about a 3 out of 6. Though the telescope I was using was much smaller than the ones listed in the 1964 report, I was unable to see any red or blue bands or any other color changes in Aristarchus during that time. I was able to pick out at least two of the "normally seen" dark bands on the western rim of the crater. I also noted that the dark area surrounding Aristarchus really stood out tonight, though I didn't think it looked unusually dark. I was able to get a pretty decent photo of the area at 1:40 AM when the terminator longitude was at 129.39 degrees. The photo is below:
I sent my report and the photo to Dr. Cook, and the next day he emailed to let me know that I'd get a mention in the May TLP newsletter. If so, this would be the second time for me.
My goal is to observe this area and image it as often as possible, whether I'm seeing it during a repeat illumination event or not. I'm collecting photos of it under as many different lighting conditions during each lunar cycle as I can in order to get a good idea of how Aristarchus and the adjoining area looks during lunar morning, high noon, and lunar evening ... how the shadows look, which areas get brighter as the sun gets higher, and so on. I may never see a TLP (they might not even exist!) but the fun for me is in the hunt for one!
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