Darkness at Moon

Yesterday, as I finished reading the current issue of New Scientist, I turned over the last page and was struck by a watch advertisement on the back cover. The wristwatch appeared to be in lunar orbit, and had the kind of multi-dial face meant to appeal to a would-be astronaut. Indeed, according to the ad copy, earlier iterations of this very model, an Omega Speedmaster chronometer, were worn by members of the Apollo missions. In and under the headline, "THE DARK SIDE OF THE MOON," the ad's text referred twice to an outpost that only right-stuff crews have seen "with their own eyes."

I made that same labeling mistake once myself, and was embarrassed by it, so I remain sensitized to the important difference between the far side of the Moon, forever hidden from the earthbound among us, and the dark side, which changes all the time as the Moon circles the Earth. At full Moon, the dark side and the far side are one and the same. But the same cannot be said for the rest of any month. Most times, moonstruck earthlings can easily see our satellite's dark side without benefit of a rocket ship or even a telescope.

Grade-school teachers report that the majority of students need to engage in hands-on activities involving globes and flashlights before they can master the Moon's phases. For whatever help it may provide, a schematic diagram of the lunar phases is pictured on every page of this web site. The old-fashioned image comes from an outdated textbook, but it contains correct information, gleaned from observers' longstanding fascination with the waxing and waning of the Moon.


Colors of the Moon

My friend Sally James (aka Dr. Sara James, Professor of Art History at Mary Baldwin College) visited me this past weekend, fresh from a week-long seminar in New York about scientific techniques for analyzing and dating works of art. I had been Sally's house guest in Staunton, Virginia, for most of May, when I taught a short course in "Writing Creatively about Science" for Mary Baldwin students. The planets Mercury, Venus, Mars, and Jupiter were clustering in attractive dawn patterns during much of my stay, but every time we set our alarms early to observe them, the weather foiled us. As consolation, I suggested Sally fan her interest in astronomy by starting a Moon journal: She would look for the Moon every day and night; write down where and when she found it, and describe how it looked in those moments.

The following month, while on vacation at Wrightsville Beach, North Carolina, Sally got two of her granddaughters to keep Moon journals, too. On the evening of June 15, while a lunar eclipse unfolded over parts of Africa, the Middle East, central Asia, and western Australia, Sally saw the full Moon rise out of the Atlantic looking as red and gold as autumn leaves. She took several photos of it.

Having heard that the Moon turns red when submerged in the Earth's shadow, she wondered whether the color she'd captured with her camera had anything to do with the night's big event on the other side of the world.

In fact the Moon as viewed from North Carolina owed its redness to effects entirely unrelated to the eclipse. Just as the Sun glows reddish near the horizon at sunrise or sunset, the Moon, too, may blush while rising or setting, as its light (the sunlight reflected by the Moon's surface) travels through the thick, dust-laden lower atmosphere. The ocean mists may also contribute a reddening effect. Sally's later photos showed how the Moon whitened when it climbed higher into the sky.

We had a "new Moon," meaning "no Moon visible," for Sally's brief stay here. We sat outside till late on her last night, watching the Milky Way, counting occasional meteors even as lightning flashed in the west.