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A total lunar eclipse occurs when the moon enters the shadow of Earth and gets cut off from all direct sunlight. This can only happen at full moon when it is directly opposite the sun as seen from Earth. If the moon's orbit was in the same plane as the Earth's, a total eclipse would happen every month. The orbit is tipped about 5° however, so the moon is more often out of alignment with the sun and Earth when it is full. The Earth constantly casts a shadow out into space directly away from the sun. The darker inner shadow, the umbra, forms a cone of darkness where no direct sunlight hits. Around that is the penumbra, a lighter semi-shadow where varying amounts of sunlight falls. The diagram below shows the shadow in relation to the moon, and a hypothetical lunar eclipse with the moon traveling directly through the shadow's center.
Then there is the matter of the uneven illumination on the lunar surface. This is mostly due to the moon's path through the shadow. If it went directly though the center of the umbra, and the Earth's atmosphere was completely uniform, the eclipsed moon would appear evenly lit. That is rarely the case however, and in the eclipse pictured above (from September 1996) the moon passed near the edge of the umbra where the shadow is a little brighter. When viewing a lunar eclipse with the naked eye, you will not see such spectacular bright colors at totality. Binoculars will show the rich hues much better, and of course photography captures them best. The image above was from my film days. It was taken on the richly saturated Velvia film. The image below is from the August 28, 2007 eclipse photographed with a digital camera for a better color rendition and contrast control.
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It is worthwhile seeing a variety of lunar eclipses that occur in different parts of the sky and time of night. When seen in twilight, like the one pictured at left, the eclipsed moon will appear quite dim and ghostly. That image is from South Mountain Park in Phoenix during the early evening of November 8, 2003. If seen while the moon has just risen and the sun just set, you would have the chance to also see the Earth's shadow in the atmosphere along with the shadow effects on the lunar surface. The clearest view of the totally eclipsed moon itself is when you can see it high in a dark sky. Due to the opposite positions of sun and moon during these events, this view would occur within a couple hours of midnight. |
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| Map courtesy of Fred Espnak, NASA GSFC. For more information visit the NASA Lunar Eclipse Page
You can also view the full page of eclipse data from which this map was taken |
Feb 21, 2008 Eclipse MapThe next total eclipse of the moon will occur on February 20-21, 2008. Below is a handy map showing the circumstances of the event. People viewing from the area in white can see the entire eclipse. The closer you are to that area, the more eclipse you will see. Here is where you get to use the contact point names (P1, U1, etc.) from the diagram above.Take the U1 point for instance. It goes right along the west coast of the United States. A person in Eureka, California could see the first dark bite taken out of the moon just as it rises. They would then see the rest of the eclipse from that point. Someone along the U1 line on the other side of the world, say near the India-Pakistan border, would see that same first umbral contact just as the moon sets. They would then miss the rest of the eclipse. In another example, viewers along the U3 line in eastern Africa could witness the first bit of direct sunlight hit the lunar surface at the end of totality just as the moon sets. So they would have seen the first stages all the way through totality—still a very good eclipse experience.
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All images are copyrighted by Frank Zullo. Please do not use without written permission. |
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At left is a totally eclipsed moon showing some interesting phenomena that needs a bit of explanation. Such as, why is there so much color if the umbral shadow has no light? Although no direct sunlight hits the lunar surface, there is indirect light that is refracted into the shadow by Earth's atmosphere. This sunlight basically skims past the Earth through a long stretch of air, and much like the light we see at sunset, has the shorter wavelengths of blue and green light scattered, letting only the longer wavelengths of reddish light pass. If we were on the moon looking back at Earth at the time of totality, we would see a bright ring of orange-red light encircling the planet.
A total eclipse of the moon is not as spectacular as one of the sun. The good thing about the lunar variety is that they are much more frequent for any given location on Earth. A lunar eclipse occurs out in space and you merely have to be in sight of the moon to see it. During a typical eclipse more than half the world can witness totality. Fewer people get to see a total solar eclipse because they occur for very small areas on the Earth's surface where the sun and moon alignment are perfectly centered.