The Moon’s disappearing act

WAUKESHA, WISCONSIN: On Wednesday evening, October 27, people throughout North America will have front-row seats to their last total eclipse of the Moon until March 2007. For 81 minutes, the Moon will lie completely immersed in the darkest part of Earth’s shadow, and the only light hitting the Moon will be the reddish glow from all of our planet’s sunrises and sunsets.

Few sky events can rival the majesty of a total lunar eclipse. Watching the brilliant white Full Moon gradually transform into an orange-red globe — hanging in the autumn sky like a celestial jack-o’-lantern — is a sight you won’t soon forget. The solar system will create one of those memories Wednesday night when Earth passes directly between the Sun and Moon.
Astronomy readers can tour the cosmos during the eclipse
If clouds prevent a view of the eclipse, Astronomy readers will be able to access “Slooh … Live SpaceShow” through Astronomy.com and enjoy the progression of the colorful golden and copper tones of earthshine on the eclipsed Moon. The night of October 27/28, “Slooh … Live SpaceShow” has scheduled frequent Moon observations among its usual roster of deep-sky objects. “Slooh … Live SpaceShow” will seize the opportunity of a blacked-out Moon during totality to observe delicate details of deep-sky objects.

“Slooh … Live SpaceShow” is the world’s first and only source of live celestial images. Every night, “Slooh … Live SpaceShow” delivers live views of galaxies, nebulae, and planets from a robotic observatory in the Canary Islands. To use “Slooh … Live SpaceShow” all you need is a PC or Mac with a 56Kb-modem Internet connection. Astronomy readers can use their subscriber or newsstand number found on page 5 of every issue to log on to Astronomy.com and take advantage of this exciting opportunity.
The eclipse from the Moon’s perspective
If you were an astronaut standing on the Moon during totality, you would see Earth eclipsing the Sun. Earth would appear as a dark disk surrounded by a brilliant red ring — our atmosphere glowing with the light of all the planet’s sunsets and sunrises. It’s this light we see bathing the Moon during totality.

No one can predict the exact color of the Moon during an eclipse, which depends on conditions in Earth’s stratosphere. A major volcanic eruption can choke the stratosphere with aerosols, darkening the Moon significantly. (The Moon nearly disappeared from view during the first few total eclipses following the 1991 eruption of Mt. Pinatubo in the Philippines.) Most recent eclipses have been on the brighter side, although a major eruption by Mount St. Helens or some less-well-known volcano could darken the Moon.

The eclipse
The action starts when the Moon first touches the lighter, outer part of Earth’s shadow, called the penumbra, at 8:06 P.M. EDT. [Editor’s note: See the table below for the times in your time zone.] Unfortunately, the penumbra imparts only a subtle shading to the lunar surface, and few observers will notice more than a dusky shading on the Moon’s western half during the next hour. (From the West Coast, the Moon rises after the penumbral phase is underway.)

The real show begins when the Moon crosses into the darker, inner part of Earth’s shadow, called the umbra, at 9:14 P.M. EDT. Initially, the shadow will appear black in contrast to the rest of the Moon, which remains bathed in bright sunshine. As the partial phases progress over the next hour, however, and more of the lunar surface slips into Earth’s shadow, the Moon starts to take on a dull orange to reddish hue. The color brightens significantly by the onset of totality, which arrives at 10:23 P.M. EDT.

At first, the color may be surprising – after all, how can light get into our planet’s shadow? If Earth were an airless planet, the shadow would be pitch black, and the eclipsed Moon would vanish. But our atmosphere acts like a filtered lens, bending red sunlight into the shadow and scattering out blue light. It’s the same reason sunrises and sunsets appear reddish.

Totality will last 81 minutes, ending at 11:45 P.M. EDT. Expect the Moon’s southern half to appear darker because it passes closer to the center of Earth’s shadow. In the 2 hours after totality, the Moon gradually slides back into full sunlight, playing out the earlier partial phases in reverse. The Moon leaves the umbral shadow at 12:54 A.M. EDT and the penumbral shadow at 2:03 A.M. EDT, wrapping up the 6-hour show.

North America won’t be the only continent to see the total eclipse. Viewers throughout South America will see a similar display. And totality will reign in Europe and western Africa as well, but there, the eclipse takes place in the predawn hours of October 28.