Rhymes with June and Spoon: how well do you really know the moon?

There's a moon in the sky / It's called the moon." These lyrics from a late 1970s song by the B-52s might have been deliberately dopey, but they happen to capture a couple of truths about Earth's only natural satellite (aside from the fact that it's in the sky and it's called the Moon). First, they correctly summarize the total knowledge about all matters lunar that many people have. Second, they accurately reflect the total knowledge about all matters lunar that even many amateur and professional astronomers care to have.

After the Sun, the Moon is probably the celestial object that's easiest to take for granted. Novice observers testing a first piece of equipment might take a moment to point their new binoculars or telescope at the brightest object in the night sky, to marvel at the mountainous terrain and shadow play that originally fascinated Galileo in the autumn of 1609. But then they turn to more distant, and more exotic, targets, as if the Moon has nothing to show us but phenomena we've known about for millennia (such as phases) or at least for centuries (such as craters). For many astronomers, familiarity with the Moon has bred not contempt but indifference.

Still, a sky watcher can continue to find in the Moon the twin rewards of observational astronomy: challenge and discovery. The challenge in the case of the Moon can be to actually find it. Not when it's full and overhead and the sunlight reflecting off its surface is flooding night on Earth, but when it's new--when the Moon is lying between the Sun and you, when the disk is fully unilluminated. At such times, moonrise and moonset almost exactly coincide with sunrise and sunset, in which case you can forget about seeing the Moon.

But what about a day later? How soon can you spot the fresh crescent? For observers who look forward to this particular challenge, March offers one of the two best opportunities of the year to see a Moon that's less than a day old (the other comes in early September). The Moon turns new at 9:03 P.M. EST on March 13. The next evening, for the first half hour or so after the 6:00 P.M. sunset (or twenty-one hours after the new Moon on the East Coast, twenty-two hours in the Midwest, and so on), the slenderest of crescents will still be above the horizon--just high enough to see it if your western horizon is absolutely without obstacles, the weather is cooperating, and your eyesight is keen.

But don't stop there. On March 15 the crescent will be just wide enough to be easily evident to the naked eye and will be hovering above the horizon until 7:30 P.M., a good ninety minutes or so after sunset. Shining nearby will be a breathtakingly brilliant, nearly -4.0 magnitude Venus, which itself will set about an hour after sunset. The sight should be sufficiently spectacular to make even the most Moon-fatigued observer look twice.

But don't stop there, either. Continue to follow the Moon through its phases until the end of the month, and perhaps you'll make the same discovery I once did: the Moon isn't a circle; it's a sphere. I claim no originality for this observation, but it sure shook my world.

Two or three years ago, I looked out my living room window one morning and saw, hanging above the Manhattan horizon, a waning gibbous--or just past full--Moon. It would soon be setting, past the skyscrapers to the west, but at the moment it was catching the rising Sun's rays behind me, somewhere beyond the East River and Queens. The Moon looked so big, so luminous against the purple sky, that I reached for a telescope I keep in my desk drawer.

When I looked through it, I found craters, which I expected. I found shadows, which I expected. What I didn't expect, however, was the third dimension.

I didn't expect it even though I knew it was there. We all know it's there. We all know when we look at the night sky that it's not the flat surface it appears to be, that it has depth. But the difference between knowing and knowing--between accepting a fact intellectually and experiencing it for oneself on a deep emotional level--can be more profound in astronomy than in many other human endeavors.

Through the telescope that morning, I could see the surface of the Moon receding, curving back, angling away from the Sun and around the lunar horizon and out of sight. Here, unmistakably, was a sphere, and this sphere, equally unmistakably, was just hanging there. By itself. In space. Untethered, unsupported, unbound. Loose in the universe.

Just like Earth.

Just like me.

I had to sit down. Fortunately, a chair was there when I did. Which is why I recommend that anyone hoping to make impromptu astronomical observations should consider keeping handy three indispensable tools: a telescope or binoculars; a chair; and the knowledge that there's a planet in space, and it's called the Earth.

Richard Panek's next book, The Invisible Century: Einstein, Freud, and Our Search for Hidden Universes, will be published next year by Viking.

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