HOW COME? The many faces of the moon

Why does the Moon have different phases and crescent shapes? -- Elias DeBourg, a student in Brookville

Don't like the shape of Monday night's late-rising moon (a crescent, coming into view on the horizon at 2:23 a.m.)? Just wait around a day or two. As a month passes, the moon looks subtly different each day, blooming to a full circle, shrinking back to a sliver, and then disappearing into blackness. The day after the moon does its vanishing act, a tiny sliver rises into the sky, kicking off a whole new cycle.

The moon is like a dancer on the stage of space, lit by the spotlight of the sun. Sometimes she's in full light; sometimes only half of her body is lit. And sometimes, she's hidden in the shadows.

How does it work? The Earth and its moon travel together around the sun. Although the face of the sun is hidden below the rim of our planet at night, its light still strikes our rocky, gray moon. Since the Earth and the moon are always changing position in relation to the sun, the play of light and shadows on the moon's face constantly vary as the month wears on.

(Of course, you could see a full moon every night if you wanted to -- just hop a rocket into space. Remember, when it's night for people on one side of our planet, the other side basks in sunlight. Likewise, half the moon is always lit up. But from our fixed positions on Earth, our glimpses of daytime on the moon change daily.)

When we see one entire side of the moon lit by the sun, the moon is said to be full. The full moon occurs when the sun and the moon are on opposite sides of our planet.

But as the month passes, we see less and less of the lit face from our vantage point on Earth. Scientists say that the moon is "waning." When the moon's face is less than full -- but not yet half dark -- the phase is called a "gibbous" moon, from the Latin word for "hump." Next comes the half-lit moon. Finally, as the sun's spotlight shrinks from our perspective, we see a smaller and smaller silvery sliver -- the beautiful crescent moon.

The day after the moon has shrunk to a slim line, the moon will seem to have vanished. This "dark" phase is called the new moon -- a moon waiting to be born. The dark moon occurs when the moon and the sun are on the same side of the Earth, with the lit-up side of our satellite facing away from us. Now the whole cycle repeats, with the moon's lit face gradually "waxing" to fullness once again.

View a moon phase calendar with images of the moon for each day of the month at www.moonconnection.com/ moon_phases_calendar.phtml.