ASK A SCIENTIST
Question: What causes a lunar eclipse and what causes the reddish color to appear on the moon?
Eclipses have been observed by people all over the Earth since the beginning of time. The public's fascination with eclipses remains even in today's technological world. Lunar eclipses result when the Sun, Earth, and Moon make a straight line, with the Earth in the middle. At this time the Moon's orbital motion carries it through the Earth's shadow. Lunar eclipses are darkest when the Moon passes through the center of the Earth's shadow or umbra. Depending on the exact celestial geometry, total lunar eclipses can last up to 100 minutes. On average someone in the Binghamton area will see about 3 total lunar eclipses every 5 years, weather permitting- of course!
Since our planet has an atmosphere, some of the Sun's light is bent or refracted around the edge of the Earth, brightening its shadow somewhat. In addition, the dust in the Earth's atmosphere scatters out some of the blue light from the Sun, leaving the shadow with an orange or red tinge. Since the amount of dust and cloud cover varies in the Earth's atmosphere during any lunar eclipse, each eclipse is unique in its color and appearance.
Unlike a total solar eclipse, which is visible only from narrow path on the Earth's surface, a total lunar eclipse is visible from the entire nighttime side of the Earth. As a result most people can see dozens of total lunar eclipses in their lifetimes.
The next total lunar eclipse visible from our region will be on March 3, 2007. If you want to study this eclipse in more detail, I recommend using binoculars and a simple Moon map obtained from a local library to sketch the Earth's shadow as it covers some of the larger craters on the Moon. For more information you can call Kopernik Observatory at 607-748-3685 or visit NASA's website.
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