Observing the Moon: Copernicus

Jack Kramer

Copernicus is one of the most prominent craters on the Moon, with walls that soar over 11,000 feet above the mean lunar surface. It's full of easily-visible detail during all phases, but especially when it lies near the terminator. Use high magnification to get a better look. And be sure to have a large scale lunar atlas handy to find your way around the area.

One feature is the jumble of multiple central peaks. How many of these you can spot depends on the resolving power of the telescope you're using, along with the sky conditions. One observer using a 41/2" reflector reported seeing three of the peaks. I saw three clearly in my 3" refractor and the shadow of a fourth. Earth-based observers using larger telescopes have identified six peaks - three are fairly large and the rest are small "bumps". However, high-resolution lunar orbiter photos show still other small peaks. It's best to look for them when the Moon is between nine and ten days old (i.e.: between nine and ten days past new Moon). A day too early will leave the crater floor in total darkness from the rim shadow, and a little later in the lunar month results in a lack of contrast due to insufficient shadow.

Just to the south of Copernicus are two small overlapping craters, Fauth and Fauth A. With low magnification, they appear as a single oblong crater, but switching to higher power will clearly split them. They were easy in my 3" refractor at 135x. These craters are outside the image shown above and to the left (south).

Near Copernicus are several rills -- long cracks or gashes. High magnification discloses that most of these seem to be long, winding chains of small craterlets. Just outside and to the right of the picture (to lunar north) is the Stadius IV Rille, which appears deeper and smoother than the others.

High resolution photos disclose long, fairly straight scars positioned radially around Copernicus, and other large craters as well. One opinion is that they're marks left from the original impact where rocks and debris were thrown out at low trajectories. Another view is that they're the result of the lunar crust sinking into sub-surface voids caused by volvanic vents. The gashes around Copernicus are generally too small to be seen by our telescopes. However, the rays emanating from it are easy. When the Moon is near full, the rays are especially prominent and appear sinuous rather than fairly straight, as in the case of other large craters. In a windless, airless environment, how would ejecta assume this appearance? Could it be that the impact caused the material to be lofted high up, then it settled out in a meandering pattern due to collisions between particles?

Despite the rugged appearance of Copernicus, photographs taken by spacecraft just above the surface show that the walls aren't as jagged as you'd expect. Instead, as with many other lunar formations, they have the appearance of steep, rolling hills. The following image from Lunar Orbiter 2 shows the interior of Copernicus with the central peaks in the middle.

Copernicus is easy to identify because it stands out pretty much by itself in an uncluttered area directly to the south of the large Mare Imbrium basin. I've found myself often using it as the starting point to more quickly locate other features. Once you've decided on those formations you want to observe, then using a lunar atlas, it may be of help to determine where they lie with respect to Copernicus.

Published in the October 1997 issue of the NightTimes