Accessories for Lunar Observers

There are a few items that can make lunar exploring more productive. The most important is a map of the Moon or a lunar atlas. Luna's face is a maze of confusing details, and a map is mandatory for making sense of the landscape. At first, a simple

Plate 50. (Aris-tarchus) Bright Aris-tarchus lies in the midst of one of the Moon's most interesting and mysterious areas. Credit: Author.

large-scale map such as one found in many general observing guides will suffice. If the Moon becomes a real interest, though, something more detailed is called for. Antonin Rukl's Atlas of the Moon is the standard reference for amateur "lunatics." This is a true atlas, with the Moon's entire visible disk portrayed in considerable detail in large and beautiful airbrushed maps. Unfortunately for CAT owners who use star diagonals, the view in an SCT is mirror reversed and will never match the Rukl charts. That can be dealt with by copying charts onto transparency film with a Xerox machine and flipping them over for a correct view.

Or take the easy way out and use a computerized lunar atlas. Just as computer programs dominate in the star atlas business, computerized Moon maps are now making their presence felt. See Chapter 10 for details on specific programs. In addition to showing detail far smaller than that in Rukl or other books, computer atlases have one huge strength: their views can be flipped or rotated to exactly match the orientation seen in the telescope.

The Moon is not dangerously bright, but it is bright enough to make it sometimes difficult to see small details because of the glare. Some observers turn to Moon filters to dim Luna down a bit. These are usually neutral density filters and are not colored but only serve to reduce the intensity of the light. Like most other astronomical filters they screw onto the field lens end of an eyepiece. Moon filtersare not highly recommended for lunar observing. They reduce light too much for many telescopes, even when used at low power. They also don't do anything to enhance the appearance of the Moon's features. All they do is attenuate light. A slightly better choice for someone who wants to reduce Luna's silv'ry light is color eyepiece filters. These can work as well as a Moon filter to minimize the glare, and some colors have the added benefit of enhancing surface detail. An 80A blue filter, for example, increases the contrast of small details. A #15 yellow makes crater ray systems and rilles pop out of the landscape.

Does the CAT's drive need to be adjusted when observing the Moon? Most go-to SCTs have a Lunar Drive Rate selection in the hand controller menus. Since the Moon moves at a speed slightly faster than sidereal rate, switching over to the

"Lunar" position allows the telescope to track the Moon with more precision. Some computerized telescopes even switch to Lunar tracking speed automatically when the Moon is selected as a go-to target. In practice, the difference between sidereal and lunar rates is small enough so that you needn't bother changing the drive speed.

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