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Sierra Daily

12/08/2011

An Early Morning Eclipse

12-9-11 Total Lunar Eclipse Piotr Ciuchta
The moon emerging from a total lunar eclipse. Credit: Piotr Ciuchta

A total lunar eclipse occurs when a full moon lines up with Earth and the sun such that the moon enters into Earth's shadow. Who gets to view the eclipse is determined by what part of Earth is facing the moon at the right time. On the morning of Saturday, December 10, 2011, a lunar eclipse occurs that is situated perfectly for Asia but a bit sketchy for those of us in North America. The partial phase of the lunar eclipse begins at 12:45 UT, with the total phase beginning at 14:06 UT. Complete totality lasts for just under an hour, ending at 14:57 UT. Then the partial phase repeats as the moon slips back out of Earth’s shadow, with the event concluding at 16:17 UT.

Convert Universal Time to your local time to know when you should be looking. For those on the West Coast, that means you will have the best chance to see it. The total eclipse begins at 6:06 a.m. PST, 7:06 a.m. MST, 8:06 a.m. CST, and 9:06 a.m. EST. The problem with these times is that when the total lunar eclipse begins for those on the East Coast, the moon will already have set. So, for example, in Denver the moon sets at 7:12 a.m., allowing for observers to see all the partial phase but just a peek of the total phase.

Some of you may remember that there was a solar eclipse only last month, although it was just a partial eclipse far down on the southern tip of the world. Lunar and solar eclipses always occur within 14 days of each other. So next year when there is a solar (annular / ring-type) eclipse on May 20, there will be a lunar (partial) eclipse on June 4. But the next total lunar eclipse won't occur until April 15, 2014. The 2014 eclipse will also favor West Coast observers.

If you get to view the total phase of the lunar eclipse on Saturday morning, pay attention to just how dark the moon gets. The darkness of the moon varies from eclipse to eclipse, depending on how deep into the shadow the moon is during the eclipse and also on the atmospheric phenomena in the part of the world from which you are viewing. Brighter eclipses are more common with darker eclipses being rarer. The Danjon Scale is a measurement of the brightness of lunar eclipses. Use the definitions below to try to determine what this lunar eclipse looks like to you.

  • 0              Very dark eclipse. Moon almost invisible, especially at greatest eclipse.
  • 1              Dark eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.
  • 2              Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra  is relatively bright.
  • 3              Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
  • 4              Very bright copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.

-- Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.

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