We skywatchers have an ongoing romance with the Moon, and our nearest celestial neighbor never seems more alluring than when it’s round and bright. For me, the rising full Moon is so compelling, so magical, that I have to stop whatever I’m doing to look at it. There’s something spectacularly different about the sight of that brilliant, seemingly enormous orb hovering among the clouds, as if it were located somewhere in the outer reaches of Earth’s atmosphere — or, perhaps, in a gigantic storybook illustration.
Astronomers often consider strong moonlight to be a glaring nuisance that drowns out the dim glows of distant nebulas and galaxies. But as you’ll discover when you study it closely, the full Moon has its own sights to offer, ones that just aren’t available at other times. And you can see them not only on the night of the full Moon itself, but for a night or two before and afterward.
Start your exploration simply with your unaided eyes. First, notice the mottling of dark and light areas on the lunar surface, corresponding to its “seas” of frozen lava, called maria (pronounced MAH-ree-uh), and its rugged highlands, called terrae. Seen just by eye, the pattern of dusky patches seems to form a picture. To some people, it looks like a face — the “Man in the Moon.” Others see a rabbit, a toad, or a woman’s face.
The brightness of the full Moon actually reveals something unusual about its surface, which is covered with a thick layer of fine-grained dust. Usually, sunlight hitting a rough, rocky surface gets scattered all over the place. But scientists have discovered that the uppermost part of the lunar dust layer has a peculiar property, on a microscopic scale, that causes it to reflect light most strongly right back in the Sun’s direction (a phenomenon called backscattering). When you look at the full Moon, sunlight is streaming onto its face from directly behind you, and the lunar dust bounces most of the light back in your direction — just as a stop sign strongly reflects the glare of your car’s headlights. The effect is quite powerful: from our perspective a full Moon has only twice the illuminated area of a quarter Moon, yet it’s 10 times brighter.
Seen through binoculars, the lunar face starts to reveal more detail. In particular, the boundaries of the dark maria become more distinct, and you’ll see that they’re all more or less circular in shape. Some 4 billion years ago, the young Moon endured a ferocious pummeling from asteroids and comets that left its surface heavily cratered. The largest impacts blasted scars hundreds of miles across and fractured the crust to great depth. Over time molten rock worked its way up through the fractures and completely flooded the great basins, a hot topping that varied in thickness from several hundred feet along the circular rims to as much as 1 or 2 miles at their centers. You can think of the maria as huge saucers of solidified lava.
A Splashy Appearance
Your first view of the full Moon through binoculars or a telescope might seem bland at first. The scene lacks the dramatic shadows that make lunar features stand out at other times. But there are still plenty of details to explore, and they have fascinating stories to tell.
The most striking things you’ll notice on the Sun-drenched landscape are bright, star-shaped patterns emanating from several large craters. These patterns, called rays, are streaks of rock and dust splashed over great distances by the impacts that formed the craters. The most spectacular example surrounds the 63-mile-wide crater Tycho in the southern highlands; its rays stretch up to 1,100 miles to the northeast and always remind me of a spray of fireworks. The crater Copernicus, located within the large mare called the Ocean of Storms, has a system of feathery rays stretching for more than 700 miles in all directions.
-- Continued on Page 2© 2006 Reprinted with permission from Sky Publishing Corp.
