Winter Solstice Lunar Eclipse

(NASA Photo)

A spectacular lunar eclipse is visible across the skies of North America, just hours before the winter solstice, on the night of December 20/21, 2010.

A lunar eclipse is visible when the moon, at the full phase, moves into the Earth’s shadow.  Occurring infrequently because the orbit is tilted slightly compared to the earth’s solar orbital path, the moon usually moves above or below the shadow when on the opposite side of Earth from the sun.

As the moon slowly plunges into the Earth’s shadow, it loses its reflected sunlight.  A total eclipse is not completely dark, but some red and orange sunlight is refracted into the shadow.  The moon then has a reddish orange glow.

Earth’s shadow has two zones:  The penumbra is the outer part of the shadow where the sunlight is not completely blocked.  The umbra is dark because it receives no direct sunlight.  During the nighttime we are inside the earth’s umbra.  No sunlight is visible.

Lunar eclipses are seen more often from any one location as they are visible from over half the earth, where the moon is above the horizon.  A lunar eclipse is not dangerous to view.  Binoculars or a telescope under low power, 15x to 40x present outstanding views of the eclipse.

Here are the events for the evening:

December 20, 2010  (The times that follow are accurate for any location in North American, except times for sunrise, sunset, moonrise, and moonset.  Observers in other time zones can adjust the eclipse times by adding or subtracting their time zone difference from Central Standard Time.)

  • 3:50 p.m. CST (Chicago) — The moon rises in the east-northeast sky.
  • 4:22 p.m. CST — Sunset.  Throughout the evening, the moon rises higher in the eastern sky.
  • 11:30 p.m. CST — The moon begins to move into the penumbra.  Not much darkening is noticed.

December 21, 2010

  • 12:32 a.m. CST — The moon moves into the darker central shadow, the umbra.  The partial phases of the eclipse begins.  As the eclipse progresses, more of the moon grows darker.  The moon appears high in the southern sky during this part of the eclipse.
  • 1:40 a.m. CST — The moon is completely immersed inside the umbral shadow and the best part of the eclipse begins.  For the next 73 minutes, the moon may be illuminated by a soft coppery color, like the image above.  Some sunlight streams through the earth’s atmosphere and is bent into the shadow by the air’s prismatic effects.  The brightness and depth of color will depend on the amount of dust suspended in the Earth’s atmosphere.  Volcanic ash suspended at high altitudes is one factor that can affect the colorful display.
  • 2:53 a.m. CST — The moon begins to exit the umbra and the total phase of the eclipse is finished. 
  • 4:01 a.m. CST — The moon is fully inside the penumbra continuing to exit into bright sunshine.
  • 5:04 a.m. CST — The eclipse is finished.
  • 7:14 a.m. CST — Sunrise
  • 7:31 a.m. CST — Moonset
  • 5:38 p.m. CST — Winter Solstice

The next lunar eclipse visible from North America occurs on June 4, 2012.  The start of the eclipse occurs June 4, 2012, although it completes after moonset.  The next total lunar eclipse visible from the Americas is on the night of April 14/15, 2014.

For more information about lunar eclipses and general sky watching, see the Waubonsie Valley High School Planetarium website.

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