This Weekend’s Total Lunar Eclipse

Lunar EclipseAfter a drought of 2½ years, we can finally look forward to a total lunar eclipse on the evening of March 3, 2007. On that night the Moon gradually slides into and out of the shadow cast by Earth in space. It is one of the grandest and most beautiful events in nature!

We haven’t had a total lunar eclipse since October 27, 2004 — which coincidentally took place during the decisive Game 4 of the World Series between the Boston Red Sox and the St. Louis Cardinals! Yet March 3rd’s event will be the first of three total lunar eclipses to take place within the next 12 months.

Unlike a solar eclipse, which you have to view through a special protective filter to protect your eyes, a lunar eclipse is easy to see with any filter. And you don’t need any special equipment to view it — you can watch it with your eyes alone. But using binoculars or a small telescope will make the viewing experience more rewarding.

We see lunar eclipses when Earth passes directly between the Sun and the Moon. This geometry creates two kinds of shadows on the lunar surface. Within the outer shadow, the penumbra, the Moon is bathed in a slightly smoky cast; an astronaut standing on the lunar surface would see the Sun partly covered by Earth. Penumbral shading can be difficult to detect, especially near the beginning or end of an eclipse.

As the Moon begins to move into the central and darkest part of Earth’s shadow, the umbra, you’ll notice an obvious and ever-larger “bite” in the lunar disk. The partial eclipse is then under way. (A partial eclipse also happens when the Moon glides only part way through the umbra.)

On March 3rd, however, the Moon dives completely inside the umbra, and once that happens no rays of sunlight can reach the lunar surface directly. Even so, the Moon may glow with an eerie coppery light in the night sky, because some sunlight is refracted through the atmosphere all around Earth’s circumference, and some of this reddened light faintly illuminates the Moon.

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