The Lake County Astronomical Society

A Lunar Atlas on Your PC

Jack Kramer

Whatever your observing preference, it's a good bet that every now and then you take a look at the moon. If your lunar observing is strictly of the casual sort, then a simple moon map could be all you need. But if you'd like to really search out obscure objects on the lunar surface, then a detailed atlas is a must. If you have a computer running the Windows operating system, then you're in luck. Detailed image files from NASA's Clementine spacecraft are at your disposal.

The image shown here covers an area around the crater Tycho at a scale of 0.5 km/pixel. You can further increase the enlargement by choosing to zoom in by a factor that you stipulate; however, the image becomes seriously pixilated if you zoom in too much.

To begin with, you need two things. The first step is to download the freeware program Clementine Skimmer from the software archive of the Royal Astronomical Society of Canada (Edmonton) web site at:

http://www.edmontonrasc.com/software/software.html

This program was designed to access a NASA CD-ROM of images from the Clementine mission. (By downloading Clementine Skimmer, you can demo the software from a sample image without the CD-ROM.) If you like what you see, the second step is to go to the NASA web site at:

http://nssdc.gsfc.nasa.gov

This is the address for the National Space Science Data Center at the Goddard Spaceflight Center, which makes available a wealth of information about the space-related sciences. From here you can order the Clementine LDIM CD-ROM Vol. 15 at a cost of $10.00, plus shipping. (There are many other volumes at much higher resolution, but for this program to cover the entire lunar surface, you only need Volume 15.) I received my copy of the CD-ROM in a little over two weeks.

The images are composited so that a full moon view is presented. The Skimmer software allows you to navigate quickly around the Moon by pointing and clicking, then zoom in for a detailed image at a resolution of 0.5 km/pixel (1/4 arcsecond through your telescope). The program includes a database of more than 7,000 features. Using the Find Feature option, type in a name and the feature will pop up in a list with some basic information about it. Double-click on the feature name in the list and an image will appear with the cursor on top of the requested feature. Or start with a large-scale view of the lunar surface, then right-click on a feature to get the "identify feature" option. You can also modify the database to add your own comments. And you can save the images in a number of formats.

As the cursor moves, it provides a continuous readout of lunar Latitude and Longitude, as well as the current page in the Rukl Atlas of the Moon. Other options include flipping and inverting, and point-to-point distance measurements. There are only a couple of criticisms. On the enlarged views there is some distortion where images taken at slightly different angles apparently meet. And on a few of the features, there are insufficiently distinct shadows. As a result, they seem overexposed and details are hard to identify. In some cases, the Maria seem too dark and lunar rays far too prominent. However, the images can be made brighter or darker by the user, and the contrast may be adjusted. This is a very useful tool and I've found myself using this, rather than a printed atlas, to identify minute features on the moon.