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Copper Moon: May's Lunar Eclipse

Eclipse diagram

Mid-eclipse occurs at 3:40 UT on May 16, which is 11:40 p.m. EDT on May 15 for North Americans. The image above is adapted from an illustration in Celestial Delights and shows the course of the moon through Earth's shadow and the Universal Time for each of its contacts; subtract four hours to convert to Eastern Daylight Time. An inset shows the corresponding view of Earth as seen from the moon.
Click for the animated version.

Sky watchers from Madagascar to California will see a striking total lunar eclipse on May 16. With the moon most deeply immersed in shadow shortly before midnight Eastern Daylight Time on May 15, at least a portion of totality will be visible to observers in Europe, Africa and the Americas.

Lunar eclipses occur when the full moon passes through the Earth's shadow. The moon encounters the penumbra, the Earth's outermost shadow zone, at 1:05 Universal Time (UT). Expert observers may notice a slight dusky shading on the leading edge of the moon ten minutes or so after it contacts the penumbra. Most people won't notice anything unusual about the moon for another thirty minutes.

The moon begins its entry into the innermost shadow zone, or umbra, at 2:03 UT. For the next hour, even the most casual skygazer will notice a circular shadow creeping across the moon's face. At 3:14 UT, the moon will lie completely within the umbra. That's when it will take on an eerie coppery tint that ancient writers often compared with blood.

Without Earth's atmosphere, the moon would disappear completely once immersed in the umbra. Longer wavelengths of light penetrate Earth's atmosphere better than shorter wavelengths, which is why the rising or setting sun looks reddish. In essence, the ruddy tint of a totally eclipsed moon comes from the ring of atmosphere around Earth's limb that scatters a sunset-like glow into the umbra.

The hue actually changes from one eclipse to another, ranging from a bright coppery orange to brownish, and the moon may darken so much that it becomes all but invisible to the unaided eye. These very dark lunar eclipses often occur after exceptional volcanic eruptions, which can enhance the number of sulfuric acid droplets in the stratosphere and thus increase its ability to scatter light.

Totality will end at 4:07 UT, when the moon's leading edge exits the umbra. The moon will leave the umbra completely at 5:18 UT, and the eclipse will end at 6:15 UT when the moon makes its last contact with the penumbra. From start to finish, the eclipse lasts over five hours.

This is the first of four consecutive total lunar eclipses, part of an unusual series known as a tetrad. The next eclipse, which occurs on November 9, will be visible from the Americas, Europe, Africa, the Middle East and western Asia. The one after that, in May 2004, will favor the Eastern Hemisphere, but the final eclipse of the tetrad, in October 2004, will bring another coppery moon to the Americas.