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New Mexico State University

New Mexico State University

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Sky watchers can enjoy a total eclipse of the moon

The clear dark skies of southern New Mexico should provide a sensational show for sky watchers Thursday, May 15, when there will be a total eclipse of the moon, said New Mexico State University astronomer Kurt Anderson.

n said the eclipse will be apparent to the unaided eye -- no telescopes or binoculars will be required to observe the event, but it will be more impressive if viewed in darker skies away from the glare of city lights.

"It should be visible throughout the United States, but our skies should provide a particularly spectacular show for Southwestern observers," Anderson said.

Moonrise will be about 6:34 p.m. MDT and the lunar eclipse will begin at 7:05 p.m. when the full moon enters the penumbral shadow of Earth. In the penumbra, Earth, as seen from the moon, blocks out only a portion of the sun's light.

"This part of the eclipse won't be very noticeable, but will appear as a progressive dimming of the moon's brightness," Anderson said.

The moon enters Earth's umbral shadow at 8:03 p.m. and observers will see the sharp edge of this darker shadow of the Earth begin to move across the face of the moon, beginning on the moon's western edge.

"The umbra is the part of the shadow within which an astronaut on the moon would see the Earth completely covering the sun," he said.

The eclipse will become total, with all of the moon in the umbral shadow, at 9:14 p.m. Totality will last until 10:07 p.m., with mid-eclipse at 9:40 p.m. Between 10:07 and 11:18 p.m. the moon will move out of the main shadow of Earth. Finally, the penumbral part of the eclipse will end at 12:15 a.m. Friday, May 16.

Watchers should note the curved shadow of Earth as it crosses the face of the moon. "The shape of the shadow was offered as proof of the Earth's sphericity by Aristotle in about 350 B.C.," he said.

During "totality" the moon will probably assume a reddish hue because of the sunlight refracted by Earth's atmosphere. An observer on the moon during this part of the eclipse would see Earth as a dark disk completely obscuring the sun, but surrounded by a bright red ring of refracted sunlight, Anderson said.

Earth's atmosphere acts like a prism to bend this sunlight toward the moon, but absorption and scattering in that atmosphere removes all but the reddest wavelengths of light.

"These are the same phenomena which distort the setting sun and make it appear red," he said.

Eclipses tend to occur at six-month intervals. Another lunar eclipse will occur in November.