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Fernando Vergara, Associated Press
The earth's shadow begins to fall on the moon during a total lunar eclipse, behind the Angel Moroni statue in Bogota, Colombia, early Wednesday, Oct. 8, 2014. Skygazers in the western U.S. and Canada will be treated to a total eclipse of the moon before dawn, Saturday, April 4, 2015. Scientists said it’ll be an unusually brief eclipse, with totality lasting several minutes.

CAPE CANAVERAL, Fla. — The heavens are providing a holiday treat this weekend, but you'll have to be quick to catch it.

If there are clear skies, the 3½-hour spectacle is visible from start to finish from the western U.S. and Canada where it occurs before dawn. Skygazers in the Midwest and East Coast only get part of the lunar show.

Scientists expect totality — when the full moon is completely obscured by Earth's shadow — to last just several minutes, beginning at 4:58 a.m. PDT, or 5:58 a.m. in Utah, on Saturday.

The eclipse will be visible Saturday night from Australia and parts of Asia, and deep at night from Hawaii and New Zealand.

In the Midwest, the moon will be close to setting and the sun rising around totality. The eastern half of North America will miss out on the total phase.

HOW LONG IS THE TOTAL ECLIPSE?

NASA calculates the total eclipse — the moment when Earth's shadow completely blocks the moon — at only five minutes. Using a different model, the U.S. Naval Observatory put it at about 12 minutes. In either case, it's the shortest lunar eclipse of the century.

WHY SO BRIEF?

In this case, the moon skims the upper part of Earth's shadow. If the moon passes through the middle of the shadow, the eclipse lasts longer.

WHY A "BLOOD MOON" DURING THE ECLIPSE?

"Blood moon" refers to its orange or red appearance — the result of sunlight scattering off Earth's atmosphere. Whether the moon appears dark red, copper, bronze or another shade depends on several factors including the amount of volcanic ash in the atmosphere.

"That's what makes lunar eclipses so interesting," said Geoff Chester of the U.S. Naval Observatory in Washington.

WHEN IS THE NEXT TOTAL LUNAR ECLIPSE?

The next full eclipse of the moon occurs on Sept. 28 and will be visible across the U.S. and Canada, as well as western Europe and Africa. Totality will last a little over an hour.

IS SPECIAL EQUIPMENT NEEDED TO WATCH?

Unlike solar eclipses which require eye protection, you only need clear skies to view a lunar eclipse. A pair of binoculars or backyard telescope will enhance your view, but they're not necessary.

"Get a comfortable chair ... and just look up," said Mitzi Adams, an astronomer at NASA's Marshall Space Flight Center in Alabama.

Online:

NASA's eclipse map: http://go.usa.gov/3gwxP

Watch: http://new.livestream.com/GriffithObservatoryTV

Follow the reporter on Twitter: @SciWriAlicia