Monday, April 8, 2013

AM Sat. March 30, 2013 - Lunar Observing (Part 3)

  While I was photographing and observing the Moon that morning, I also managed to take some decent photographs of the Aristarchus / Herodotus area and also observe it with the eye under high power.

  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!




Saturday, April 6, 2013

AM Saturday, March 30, 2013 - Lunar Observing (Part 2)

  During the last post to this blog I commented on the "Mare Crisium Sunset Ray" a couple of times. I thought I'd try to post the photo of the Mare Crisium area taken last weekend along with some photos and sketches from past years to try to explain this fleeting event on the Moon a little more thoroughly.

  Mare Crisium is one of the smaller "seas" on the Moon; large flat plains of volcanic rock that are left over from giant asteroid collisions that took place billions of years ago when the Moon was first forming. It sits on the eastern edge of the Moon, and I've always found it showy because of it's dark color and because it has some pretty lofty mountains that ring it, making it a real beauty through the eyepiece when it's experiencing sunrise or sunset. This photo of the Full Moon shows the location of the Mare, using a red square:



  From two to three days after Full Moon, sunset occurs on Mare Crisium. The terminator (the line that divides day and night) creeps across the plain, craters that lie within Mare Crisium grow long shadows, and the mountains that surround it also cast shadows over the dark material of the plain. I was observing and sketching this area on the morning of February 24th, 2008 when I saw that there was a long streamer of sunlight on it's southern edge, caused by the sun shining between a gap in the mountains. I was able to see this again when I observed it on August 19th that year. Unfortunately, I haven't seen it since then. A "day" on the Moon lasts 29.5 days on Earth, and this phenomenon only takes place over a matter of hours during each Lunar Day. I haven't been able to catch the Moon at exactly the right time to see it, but hope to soon. If I do, and especially if I manage to photograph the Sunset Ray, I'll try to post it on this blog.



   To try to show what the Mare Crisium Sunset Ray looks like, and get an idea of when it might be seen, I thought it would be worthwhile to show some photos and sketches that show how this area looks as sunset happens. This is a photo I took on November 1, 2012. It shows the terminator about halfway through Mare Crisium. It's still to "early in the evening" on the Moon for the Sunset Ray to show up. Craters within Mare Crisium are showing a lot of relief because of the low sun angle and their floors are in shadow. The terminator here is at about 62.0 degrees East.


  This is the same photo from November 1, 2012 with some of the craters within and outside of Mare Crisium labeled. Mare Crisium itself is about 570 km (350 miles) in diameter. Two of the most obvious craters within it are Pierce (diameter = 11 miles) and Picard (diameter = 14 miles). Both of these craters were starting to get deep shadows across their floors. Also starting to show a lot of floor shadow was the small but sharply defined crater Greaves (diameter = 9 miles). Along the edge of Mare Crisium are two interesting flooded craters, Yerkes and Lick. These are probably craters that existed before the impact that created Mare Crisium, and when dark lava flooded that big crater that created the plain, it also flooded the floors of Yerkes and Lick. All we see are the crater rims that managed to stay intact. This photo also shows some craters around Mare Crisium, mainly for reference; Macrobius, the bright ray crater Proclus, and the flooded crater Tebbutt. The Mare Crisium Sunset Ray seems to be associated with the mountains just north of (above) Tebbutt.



  This is a sketch I made at the telescope while observing on the morning of February 24, 2008. This was the night I first noticed the Sunset Ray. It shows some of the craters that were in the photo before. The longitude of the terminator at the time was 56.9 degrees East. Since the terminator (or sunset line) moves a little over half a degree of longitude per hour, this shows how the area looked the equivalent of ten hours after the photo above it was taken. The floors of Pierce and Picard are still in shadow. Greaves also has a floor in shadow, but the shadows cast by the mountains along the western rim of Mare Crisium have nearly covered up that whole crater. The flooded crater Yerkes is still visible, but the other flooded crater Lick is also almost covered up by the mountain shadows that are starting to cover the Mare. The mountain shadows were long enough to meet the sunset line on the south (lower) part of Mare Crisium, except for the Sunset Ray which stretched across it just above the crater Tebbutt.


  This is a sketch made at the telescope of the same area on the morning of August 19, 2008; the second time that I was able to spot the Mare Crisium Sunset Ray. At the time the longitude of the terminator was at 55.8 degrees East, so it shows the area the equivalent of two hours after the first sketch, and the equivalent of about 12 hours after the photograph. The craters Pierce and Picard by this time were so deep in shadow that they looked like black ovals on the plain. So did Greaves, and it was at the edge of the shadow being cast by the mountains to the west and about ready to be covered up. Yerkes was still visible and the low sun angle made its low rim stand out more. Lick was no longer visible since it was totally covered by mountain shadow. Tebbutt was also starting to get covered by shadows. The Sunset Ray was thinner now and shorter, but still visible just north (above) Tebbutt.


   This is a photograph I took last weekend on the morning of Saturday, March 30, 2013. The longitude of the terminator here was 50.6 degrees East, so it's the equivalent of how Mare Crisium looked 22 hours after the first photograph, or how it would look 12 hours after the first sketch and 10 hours after the second sketch. Mare Crisium itself has now experienced sunset and only the mountains on the west rim are showing. (I thought the bright spot within the Mare was part of the rim of Yerkes crater when I first published photos of the Moon from Saturday in my previous post, but now I'm thinking that it's an isolated high point just inside the rim of Mare Crisium.)



  Here's the same photograph, with the craters Macrobius (diameter = 40 miles) and Proclus (diameter = 17 miles) labeled. These craters are mainly for reference so this photo can be compared to the first one in this entry.

  By compiling these photos and sketches, the Mare Crisium Sunset Ray seems to last, at most, 18 hours or so during each Lunar Cycle, but I have a hunch it can be observed for only about 12 hours at most every 29.5 days. I hope I can catch it again sometime soon, and also image it. It really is stunning to see! The fact that such fleeting details can only be seen for such a short time each month is one of the mind-blowing things about observing the Moon to me!









Wednesday, April 3, 2013

AM Sat. March 30, 2013 - Lunar Observing (Part 1)

  Bad weather and my work schedule have kept me from doing much observing at all. I haven't made any variable star brightness estimates since 2013 began. However, I have managed to get the 10" f/4 outside several times to do some Lunar Observing and Photography.

  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.