Total Eclipse: Dark of the Moon

The December 21, 2010, lunar eclipse dazzled viewers across North America. This image is a two-exposure combination taken in Mead, Colorado, by attaching a digital camera to a 4-inch telescope.
Photo by Richard McCoy

by Michael E. Bakich
Published: June 6, 2011

Don't get scared. This title is not from Hollywood Movies. The first lunar eclipse of 2011 occurs June 15. The timing and the placement of the Moon in its orbit does not favor the Western Hemisphere, however.

Skywatchers can see the entire event from the eastern half of Africa, the Middle East, central Asia, and western Australia. At mid-eclipse, the Moon will lie near the zenith for observers situated in Réunion or Mauritius in the Indian Ocean.

Observers throughout Europe will miss the early stages of the eclipse because they occur before moonrise. But except for northern Scotland and northern Scandinavia, Europeans with clear skies will see totality (when the Moon lies completely within Earth’s umbra).

Likewise, eastern Asia, eastern Australia, and New Zealand will miss the last stages of eclipse because they occur after moonset, but, like those in Europe, most inhabitants will see the total phase. Observers in eastern Brazil, Uruguay, and Argentina also will witness totality. Unfortunately, none of the eclipse will be visible from North America.

A lunar eclipse occurs when the Moon in its orbit passes into Earth’s shadow. Because the Sun isn’t a point of light, the shadow has two parts — the inner, darker umbra and the outer, lighter penumbra. If the entire Moon enters the umbra, the eclipse is total. If the umbra hides only part of our satellite, the eclipse is partial.

This eclipse’s umbral phase begins at 18h22m56s UT (2:22:56 p.m. EDT). As the Moon dips deeper into our planet’s shadow during the next hour or so, darkness gradually overtakes the brilliant orb.

Earth’s shadow takes almost exactly 1 hour to envelop the Moon. Totality begins at 19h22m30s UT (3:22:30 p.m. EDT).

The Moon won’t disappear from view, however. Some sunlight passing through Earth’s atmosphere falls on the lunar surface. The cleaner our atmosphere is, the “lighter” the eclipse will be. “Dark” eclipses generally occur after large volcanic eruptions when the atmosphere contains more dust.

What color will the Moon turn at mideclipse? During previous total eclipses, the Moon has appeared brown, orange, crimson, and brick red. Lunar eclipses exhibit a range of shades because sunlight passing through Earth’s atmosphere during totality becomes scattered and reddened. It’s this dim glow that fills Earth’s shadow and lights the eclipsed Moon. The sky certainly will grow darker, allowing the bright summer stars surrounding our nearest celestial neighbor to spring back to prominence.

Totality lasts 100 minutes, which is rather long. The last eclipse to exceed this duration was in July 2000. During totality, the Moon’s southern edge may appear slightly darker than its northern side. This disparity occurs because the Moon’s southern limb lies a bit closer to the center of Earth’s shadow. After totality ends at 21h02m42s UT (5:02:42 p.m. EDT), it takes the Moon another 60 minutes to leave Earth’s umbra.

Astronomy magazine Contributing Editor Ray Shubinski describes the upcoming eclipse as a missed opportunity: “It’s too bad that nobody in North America will see the eclipse. Luckily, we don’t have all that long to wait until the next one.”

The eclipse to which Shubinski refers will occur December 10. But it won’t be perfect, either. For North Americans, that eclipse will still be in progress as the Moon sets. The farther west you live, however, the larger fraction of the eclipse you will see before moonset. The entire event will be visible for inhabitants of Asia and Australia under clear skies.