Touring the Moon with Binoculars Adapted from SkyWatch

Courtesy Lick Observatory.

The Moon goes through its cycle of phases about once a month. It waxes from new, to a thin crescent, to quarter (half-Moon), to gibbous (football-shaped), to full. Then it wanes back through gibbous, quarter, and crescent phases to new again. Almost any calendar or almanac will give you the dates of the principal lunar phases.

At every phase except full Moon, you'll notice that the lunar globe is divided by the terminator, the line separating the Moon's bright, sunlit side from the side hidden in shadow. Here is where surface features stand out best. Seen in a small telescope or high-power binoculars, the landscape near the terminator stands out in bold contrast and detail. Here you can find a welter of mountain ranges, valleys, and seemingly bottomless craters filled with black shadow. As you move away from the terminator into the bright disk, the land seems much smoother. The terrain looks very rough near the terminator because here the Sun is near the lunar horizon. Thus every low hill casts a long, black shadow that creates an exaggerated impression of height.

The view changes constantly. As the terminator creeps across the Moon's surface night after night, shadow patterns change and new features come into daylight or vanish into darkness. Try to examine the same feature every clear night for a week or two. A crater may appear to be a deep, dark hole at lunar sunrise, turn saucer-shaped as the Sun climbs the sky over the next few days, then look merely like a white spot when the Moon is near full.

You'll see a lot more on the Moon if you can brace your binoculars firmly on some kind of support so they don't wiggle. When you are viewing star fields, low-power binoculars like 7 x 35s or 8 x 50s give a nice, wide view, but this is no advantage when Moon-watching. For the Moon, the higher the power the better -- assuming you have a steady mount such as a camera tripod to give jitter-free views. High-power binoculars like 12 x 60s and 20 x 80s work well for this purpose. Once you've mastered aiming and focusing your binoculars, you'll enjoy many hours of viewing the ever-changing face of our closest neighbor in space.

Using the Moon Map

  To use the accompanying map, turn it around until it matches the view in your binoculars. Start your tour by learning the Moon's large, dark plains, called maria (the Latin plural of mare, "sea"). Early telescope users and mapmakers in the 17th century thought these dark markings were similar to Earth's bodies of water and gave them fanciful names like Mare Nectaris, "Sea of Nectar," and Mare Nubium, "Sea of Clouds." Today we know that the Moon is an airless, waterless, and lifeless world. The maria are in fact great lava flows that filled much of the lunar lowlands billions of years ago.

(Click for larger view) A map of the Moon, our nearest neighbor in space, showing some of the major surface markings visible through binoculars and small telescopes. The dark patches are great lava flows that flooded the lunar lowlands billions of years ago. The craters were made by large meteorite impacts. North is up and lunar east (celestial west) is to the right. Photograph courtesy Lick Observatory.

When the Moon is a slender crescent in the western sky after dusk, we see the features near the right-hand edge of the map. As you can see, Mare Crisium and Mare Fecunditatis are the only major "seas" visible. In the next few days the retreating terminator gradually unveils Mare Nectaris, Mare Tranquillitatis, and Mare Serenitatis. At first-quarter phase we see the entire right half of the map. After first quarter Mare Imbrium and Mare Nubium appear, and just before full, Oceanus Procellarum and Mare Humorum come into view.

At full phase the Moon is at its dazzling brightest. Because the Sun shines onto the Moon from almost directly behind us at this time, we see no shadows of craters and mountains. The bright ray system of the craters Tycho, Copernicus, and Kepler stand out especially prominently. The rays are splash patterns of debris from the impacts that formed the craters. After full phase the advancing terminator covers up the surface in the same right-to-left order.

Unlike astronomical telescopes, which give inverted (upside-down) and sometimes mirror-reversed images, binoculars show you right-side-up views that are never mirror-reversed, making comparison with the lunar map very easy. Once the map is oriented properly, you will be able to readily identify the major seas, craters, mountain ranges, and other features. In time the geography of this alien world will become as familiar to you as that of our own.

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