Jan 18, 2000

Total Lunacy

copyright Vic Winter ICSTARS
January 19, 2000 -- Each month when the Moon is full, the coyotes in our neighborhood visit my sled dogs' kennel. Three or four coyotes gather on one side of the fence with about a dozen Siberian Huskies on the other. Before long, the "Moon song" begins. It starts with a few discordant yips and some tentative yowls. Then, just when you think the chorus is over, there's a spine-chilling explosion of howls in perfect canine harmony. No one sleeps through a full Moon where we live.

The next full Moon is on Thursday and I fully expect the usual serenade. But when my lead dog peers at the Moon this week, he might do a double take. On Thursday night and Friday morning, January 20 and 21, there will be a total lunar eclipse as the Moon passes directly through the shadow of our planet. Unlike a solar eclipse, which requires special equipment to observe safely, a lunar eclipse can be viewed with the unaided eye, even by Siberian Huskies.

Above: This time-lapse photograph by Vic Winter shows a total lunar eclipse over North America that occurred in April 1993. [more information]

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A lunar eclipse takes place when the Moon passes through Earth's shadow. This can only happen when the Moon is full. The eclipse will begin this Thursday night when the moon is high in the sky over the Americas. The face of the Moon will begin to dim at about 10 p.m. in New York and 7 p.m. in Los Angeles on January 20. As seen from Western Europe and Africa, the eclipse won't begin until a few hours before dawn on January 21. At totality the face of the Moon will likely have a deep coppery color. [see the Eclipse Time Table for details]

The Moon orbits the Earth every 29.5 days but it doesn't pass through the Earth's shadow each time it goes around. That's because the Moon's orbit is tilted with respect to the plane of the Earth's orbit around the Sun. There are anywhere from 0 to 3 lunar eclipses (including partial and total) each year. The last total lunar eclipse visible from the United States occurred on Sept. 26, 1996. North Americans won't have another opportunity to see a total lunar eclipse until May 16, 2003. However, on July 16, 2000, Hawaii, Australia and Asia will see the longest total lunar eclipse in 140 years (since 1859). It will last 1 hour and 47 minutes.

To fully understand lunar eclipses, you have to know the meaning of umbra and penumbra. The Earth's shadow has a conical shape with two parts. The umbral shadow (on the inside) is very dark while the penumbral shadow (on the outside) is very weak. An astronaut situated on the Moon inside the penumbral shadow would see the disk of the Sun partially covered by the Earth. From a position in the umbral shadow, the astronaut would see a total eclipse of the Sun by the Earth.

diagram showing geometry of eclipses

diagram of moon passing through Earth's penumbra and umbra
Lunar eclipses are considered total when the Moon passes completely into the umbral shadow. Unlike total solar eclipses, which are over in just a few minutes, lunar eclipses are slow. From start to finish, this week's lunar eclipse lasts nearly three and a half hours. The eclipse begins as the Moon's eastern edge slowly moves into the Earth's umbral shadow. During this partial phase, it takes just over an hour for the Moon's orbital motion to carry it entirely within the Earth's dark umbra. Then, totality lasts for 77 minutes. After the total phase ends, it is once again followed by a partial eclipse as the Moon gradually leaves the umbral shadow.

You might think that the Moon would be completely dark at totality. Not so. The Earth's atmosphere bends and refracts sunlight into the umbra. Even at maximum eclipse the moon is weakly illuminated. When this sunlight passes through Earth's atmosphere most of the blue-colored light is filtered out. The remaining light is a deep red or orange in color and is much dimmer than pure white sunlight. The exact appearance depends on how much dust and clouds are present in Earth's atmosphere. Total eclipses tend to be very dark after major volcanic eruptions since these events dump large amounts of volcanic ash into Earth's atmosphere. During the total lunar eclipse of December 1992, dust from Mount Pinatubo rendered the Moon nearly invisible. Since no major volcanic eruptions have taken place recently, the Moon will probably take on a vivid red or orange color during the long total phase.

During totality, the winter Milky Way and constellations will be well placed for viewing. Gemini's Castor and Pollux lie a dozen degrees northwest of the eclipsed Moon, while the Beehive cluster or M44 is 7° to the east.

Total Lunar Eclipse of January 20, 2000
Event Time
Partial Eclipse Begins 03:01 AM* 10:01 PM 09:01 PM 08:01 PM 07:01 PM
Total Eclipse Begins 04:05 AM* 11:05 PM 10:05 PM 09:05 PM 08:05 PM
Mid-Eclipse 04:44 AM* 11:44 PM 10:44 PM 09:44 PM 08:44 PM
Total Eclipse Ends 05:22 AM* 12:22 AM* 11:22 PM 10:22 PM 09:22 PM
Partial Eclipse Ends 06:25 AM* 01:25 AM* 12:25 AM* 11:25 PM 10:25 PM

* Event occurs on morning of January 21, 2000

GST - Greenwich Mean Time; EST - Eastern Standard Time; CST - Central Standard Time; MST - Mountain Standard Time; PST - Pacific Standard Time

Web Links

Sky & Telescope Press Release -On Thursday night/Friday morning, January 20/21, Americans and Western Europeans will have a front-row seat for the first total lunar eclipse in more than two years.

Total Lunar Eclipse: January 20-21, 2000 - a press release from the Goddard Space Flight Center

More information about the eclipse -from Fred Espenak at the Goddard Space Flight Center

Tips for photographing a lunar eclipse -an excellent overview from

5000 year catalog of lunar eclipses -During the 50 century period, 2000 B.C. to 3000 A.D., Earth experiences 12186 lunar eclipses.