The Libration Zones

Page 3: The West. Mare Orientale Page 1: The South East. Page 2: The North East.

Mare Orientale occupies the most pristine, multi-ring, impact basin on the Moon. Sadly it is located largely on the far side and is only visible from Earth during periods of favourable libration. As a result, the true nature of this basin was only revealed by images from spacecraft (Lunar Orbiter and Clementine). The pictures below were taken during a period of exceptionally good libration for this area. However, they had to be taken in daylight because there is very little darkness at this time of the year where I live and, at this phase, the moon only rises high in the sky after the Sun is up. However the use of an infrared-pass filter cuts out much of the glow from the blue sky and good pictures can be obtained (for other examples see here.)

The first two pictures below are both mosaics of two or three separate frames. The pictures are rather flat because the phase of the Moon (days 21.8 and 25.2) meant that the Sun was overhead on this part of the Moon and so there were few shadows. This is always a problem imaging the limb areas, either the Sun is high in the lunar sky or it is behind the camera, either way there are few shadows to bring out the detail. In particular the outer ring of mountains, the Cordillera, really do not show at all. They are steeper on the western side (the inside of the ring) and in the first picture below the Sun was about 13° west of north as seen from that part of the Moon (latitude 80° west). In the second picture, taken a day later, the Sun had only moved to about 25° from north so little more detail was showing. The third picture below was taken 2 days later when the Sun had sunk to 40° above the lunar horizon. I only managed the one frame; on day 25.2 of the lunar cycle, the Moon was only 32° higher in my sky than the Sun, so a fainter Moon was in a brighter sky making imaging even more difficult. (I should have got up earlier!) Many craters have become more visible, but the Cordillera Mountains are still not clearly visible.

I have departed from my usual practice of using the formal names on my mouseovers and the common names in my notes for the Rook Mountains. Montes Rook includes both the inner rings of the basin and are distinguished as the Inner Rook and Outer Rook mountains. Lacus Veris is a long slender strip of mare lava falling between the two rings on their eastern side. Similarly, Lacus Autumni falls between the outer Rook Mountains and the Cordillera Mountains.

Move your mouse over the picture to see the names of the various features.

	This is the same picture as shown at the top of the page but orientated more conventionally. It is a mosaic of four images taken on 26th June 2008 when the Moon was 21.8 days old. The libration was -7° 10' in longitude, -3° 44' in latitude, almost ideal for showing Mare Orientale. The mountains that form three rings around the basin are not clearly seen except for the Inner Rook Mountains on the far side of the basin which are on the limb. If you click on the image you will be taken to a page showing a picture taken two days earlier, in the mouseover of which I have tried to indicate where these three rings actually are. The scale markers are approximately 100 Km north and west and apply at Lacus Autumni. Both vary across the image. The north-south scale does not change much and the direction can be taken as parallel to the limb. The east-west direction stays much the same but the scale alters dramatically depending on the distance from the limb. I have also shown the position of the lunar equator. Date and Time: 26 June 2008 04:39 to 04:50 UT Camera: Atik 1-HS Telescope: LX200 at prime focus Capture: K3CCDTools. Low gamma, 1/250", 16% gain, ~600 frames Processing: Registax. Histogram as necessary, wavelets 1 = 10, 2 = 5 See comment below the picture below

	This picture was taken the following morning when the Moon was 22.9 days old. The libration was -6° 40' in longitude, -4° 53' in latitude, which is a little less favourable for Orientale than the previous morning. It is a mosaic of three images taken using my ETX125. This has a shorter focal length than my LX200 so that the scale of the picture is smaller. I was particularly pleased with how well the Sirsalis Rille shows up in this picture (several little arrows in the mouseover). This rille is 310 Km long by about 3 Km wide and starts at Sirsalis K and winds south between Sirsalis F and J, clips Cruger C, passes through de Vito A before curling round to disappear into the ejecta of Byrgius A. Byrgius A itself is an interesting crater. It is small, at 11 Km in diameter, but it is the centre of a bright ray system, which can be seen in these pictures. Its age does not seem to be known, but it is evidently young, probably less than 1,000 million years old. I've provided two sets of scale markers which approximately 100 Km north and west. The left set applies at Lacus Autumni, and the right set applies at Sirsalis. Date and Time: 27th June 2008 05:45 to 05:57 UT Camera: Atik 1-HS Telescope: ETX125 at prime focus Capture: K3CCDTools. Low gamma, 1/100", 15% gain, ~700 frames Processing: Registax. Histogram as necessary, wavelets 1 = 10, 2 = 5 *See comment below the image.

I have modified the way I post-process my images in Registax. After stacking, I now stretch the histogram to the maximum extent of the data within the image first and apply the wavelets afterwards. I think this produces better pictures than my old way of doing the wavelets first. In the case of histograms, each frame is stretched to fill the same range of intensities, so that when I combine them in iMerge I do not need to use the autobrighten feature which, I find, tends to produce ever darkening (or brightening) images as one stitches up a mosaic of the complete Moon.

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