National Geographic News
A 2007 lunar eclipse seen from Germany.
Lunar eclipses range in color from bright orange to blood red (file picture).

Photograph by Patrick Seeger, European Pressphoto Agency

Andrew Fazekas

for National Geographic News

Published June 14, 2011

Wednesday night the full moon will plunge into the longest and deepest total lunar eclipse in more than a decade.

(Update: See lunar-eclipse pictures from Wednesday's event.)

Sky-watchers across most of the Eastern Hemisphere will be able to watch the lunar disc turn stunning shades of orange and red as the moon becomes engulfed within the darkest part of Earth's shadow for almost two hours.

"The path that the moon is taking through Earth's shadow is almost directly through [the shadow's] center, making for the longest possible path and so the longest duration," said Ben Burress, staff astronomer at the Chabot Space & Science Center in Oakland, California.

"The last eclipse that was as long as this one was in 2000, while the next won't be until 2018, so this makes it a somewhat rare event."

(Also see: "Winter Solstice Lunar Eclipse—First in 372 Years.")

Lunar Eclipse to Last a Hundred-Plus Minutes

Because of the tilt of the moon's orbit around Earth, the moon usually passes slightly above or below Earth's cone-shaped shadow, so no lunar eclipse occurs.

Sometimes, however, the geometry is just right for the moon to cross Earth's orbital plane—always during a full moon. As all three bodies line up, the moon passes through Earth's shadow and we see a lunar eclipse.

Partial eclipses happen when the moon grazes Earth's shadow, while total eclipses occur when the whole moon passes through the shadow.

(See pictures of a 2010 total lunar eclipse.)

On June 15 Earth's shadow will start to darken the moon around 18:22 universal time, or UT (2:22 p.m. eastern time).

The total lunar eclipse will begin at 19:22 UT and will last for more than a hundred minutes. The deepest part of the eclipse will occur at 20:12 UT, as the moon plunges into the umbra, the dark center of our planet's shadow.

The last hint of Earth's shadow will slip off the moon around 22:02 UT.

Except for northern Scotland and Scandinavia, most of Europe as well as eastern South America and western Africa will see totality underway around moonrise—just as the sun begins to set on June 15.

"The best place to be is where you would be able to view the moon throughout the eclipse—and the higher in the sky it is, the better," Burress said. "From that standpoint, the best location for viewing the entire eclipse is eastern Africa, the Middle East, Central Asia, and the western tip of Australia."

From Indonesia to New Zealand, viewers will get to see the moon's face slowly eaten away by the initial stages of the lunar eclipse just before the moon sets on June 16.

This celestial event won't be visible from North America, unfortunately for Canadian, Mexican, and U.S. eclipse hunters, who will have to wait until December 10, when western parts of the continent will be treated to the next lunar eclipse.

Lunar Eclipse to Create a Blood-Red Moon?

The most spectacular and least predictable part of the eclipse is the color the lunar orb will take on during totality, Burress said.
"The redness of the moon during totality depends partly on global atmospheric conditions," Burress said. That's because the light we see coming from the moon is actually reflected sunlight.

During a total lunar eclipse, Earth blocks the pure white, direct light from the sun. But some indirect light passing through Earth's atmosphere still manages to reach the moon.

Since dust and gases in Earth's atmosphere filter blue wavelengths from sunlight, the remaining light is reddened. The moon will therefore appear to change from brilliant silver to between bright orange and blood red during a lunar eclipse.

"Also, how high in the sky the moon is during totality has an effect: The lower in the sky, the more atmosphere its light must pass through to reach the observer, and the more reddening that can occur."

(Take a moon myths and mysteries quiz.)

The best advice for sky-watchers is to get away from city light pollution as much as possible and go to places where there are no trees or houses blocking your view, Burress said.

"If you can determine where the moon will be during the eclipse, you want to choose a place with a clear, unobstructed view of that part of the sky and enjoy the show."

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