There will be a total lunar eclipse on the night of October 27, which will be visible across much of North America. Do lunar eclipses have an effect on phenomenon such as tides, avalanches and earthquakes -- how about temperature?

Well, whether or not eclipses have an effect on any geophysical phenomena, last night's total lunar eclipse certainly appears to have effected the Boston Red Sox. Or perhaps outstanding pitching and clutch hitting worked in favor of the Bosox to break the jinx that kept them from winning the World Series for 86 years.

If you were fortunate enough not to be in a cloudy location last night, and if you live in eastern North America, you likely observed the Moon turn a coppery or deep red color as the Earth's shadow crept across its face. The reddish color results from refracted sunlight streaming around the limb of the Earth. Just as sunrises and sunsets are reddened as the Sun's ray must traverse more of the Earth's atmosphere, the extraneous light reaching the Moon during a total lunar eclipse is reddened as well. Eclipses of the Moon, while just as rare as solar eclipses, are sluggish and sedate affairs by comparison. While they won't knock your socks off, they can still be quite engrossing. Besides, almost everyone on the night side of the Earth can see a lunar eclipse (weather permitting), but only a select few (relatively speaking) are fortuitously positioned to observe a solar eclipse. If you missed this one, the next total lunar eclipse similarly visible across the U.S. won't occur until February 2008!

Eclipses occur when one object moves into the shadow of another. One of the most amazing coincidences in our solar system is that the Sun is about 390 times wider than the Moon, but it's also almost exactly 390 times farther away! Because of this fact, and because the Earth, Sun and Moon happen to line up in such a manner that on occasion the Moon or Earth moves directly in front of the Sun, Earthlings can view two lunar eclipses and two solar eclipses just about every year. It turns out that the key players are lined up just right about every 346.6 days -- this is referred to as an eclipse year.

During a lunar eclipse, because the Earth is so much bigger than the Moon, it's entire surface (side facing the Earth) is engulfed by the Earth's shadow. If the Moon were populated with Lunatics, from their perspective, the Sun would disappear from the sky when the Earth passed directly in front of it. Regardless of where they were located on the Moon's surface, they would be treated to a solar eclipse. However, when the Moon was in between the Sun and the Earth, Lunatics would witness just a narrow strip of the Earth's surface being shadowed.

Eclipses don't occur every full Moon, of course, since the Moon's orbit is tilted a bit (5 degrees) with respect to the plane of the Earth's orbit around the Sun (ecliptic). So, during most full Moons, the Earth's shadow, both the umbra (deepest part of a shadow where all light is blocked) and penumbra (area of partial shadow -- only some light is blocked) misses the Moon completely.

Last week, Japan suffered a series of strong earthquakes (its worst in 10 years), and volcanoes such as Mt. St. Helens are belching smoke and steam. Is it just coincidence that parts of the Earth seems to be hyperactive of late, or do the positions of the Earth, Moon and Sun play a role in effecting or causing geophysical phenomena?

It's known that the tides during a lunar eclipse aren't significantly different than tides during a full Moon. Each is just another spring tide -- the name for tides that occur when the Earth is between the Moon and the Sun. If tides don't really differ substantially during an eclipse than during regular full Moon or new Moon phases, why should celestial positions effect the Earth's surface or subsurface features? The answer is that they don't.

Earthquakes and volcanic eruptions do indeed occur at times of eclipses. But records show that they occur with no greater frequency or power than on days when full Moons or new Moons occur (without eclipses), when all the planets line up on the same side of the Sun or on days when the Moon is in a crescent or gibbous phase. As special as eclipses are, they simply don't have a known impact on any geophysical phenomena.

Well, if it an eclipse has virtually no effect on tides, avalanches, earthquakes or volcanoes, it makes sense that atmospheric temperatures during a lunar eclipse would be unchanged from a night when the full Moon is shining brightly. However, the temperature of the atmosphere does warm up a tad when a full Moon occurs, so perhaps it's ever so slightly cooler during the total phase of a lunar eclipse?

It has been demonstrated that the temperature of the air is a fraction of a degree warmer on a night when the full Moon is in view than on nights when the Moon is absent from the sky (new Moon). Satellite measurements of temperatures in the lower troposphere have revealed that the Earth's average global temperature is approximately 0.01 degree C (a hundredth of a degree ) warmer on a moonlit night (when the Earth is between the Moon and the Sun) than when the Moon is new (between the Earth and the Sun). This doesn't really have anything to do with the greater amount of sunlight reflected from the Moon back to Earth during a full Moon. Rather, it's related to the fact that during full Moons, the Earth/Moon system is somewhat closer to the Sun than during the new Moons. It's this difference which seems to be responsible for the minuscule increase in temperature. So, regardless of the length of totality of a lunar eclipse, the Earth's temperature will remain the same.

Despite the evidence that eclipses don't impact geophysical phenomena, it's hard to know if they effect human emotions. Nonetheless, I'm glad there's not one on Halloween, or for that matter, on election day.

For more about this see
http://sunearth.gsfc.nasa.gov/eclipse/LEmono/TLE2004Oct28/TLE2004Oct28.html
See also the Science Question of the Week for April 8, 1998.

This week's question is provided by Dr. James Foster. Dr. Foster originated this series and did it as a solo project for the GSFC website for EIGHT YEARS! This year Dr. Foster has decided to share the enthusiasm he has for this project with other Goddard scientists and will be posing questions on a semi-regular basis. His question will be answered on October 22, 2004.