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July 27, 2008

Shade coming to parts of the Earth!


There will be a total solar eclipse on August 1, the first total eclipse in about 2 years. Of course I am not in the umbra, again, for the 18th time in a row but fortunately for the people who live in the northern most shit holes of the Earth- like Greenland, the Arctic, Northern Canada, and the primo vacation spot Siberia-
will get a spectacular view of the sun being totally blotted out by the moon.

A total eclipse will happen somewhere on the Earth roughly every 1.5 to 2 years and if you can hang out in one spot for at about 300 years you will eventually witness a total eclipse. Before people really knew why the moon blots out the sun, it was left up to the folklore and superstitions to explain why. Many an advisor or witchdoctor lost their head for not being able to predict this lunar miracle. Today, we know that it is not a giant dragon eating the sun or an angry god punishing the Earthly denizens.

The moon is phase locked with the Earth which is why we always see the same side of the moon. Its rotation rate equals its orbit rate around the Earth. The moon has a circular orbit but it does not follow an exact axis around the Earth, otherwise we would get a solar eclipse once a month and it would be no big deal. So sometimes it follows and latitude above our equator and sometimes below. But every two years or so it hits an axis equal to the suns and blots out the light along an umbra, or shadow. The umbra is never bigger than about 175 miles so only a small portion of the Earth will be in the exact area to see the eclipse. The rest of the Earth will see a partial, less exciting eclipse. The cool thing about the eclipse is that the moon has the right distance from Earth to block out the sun, but not entirely. What we are able to see is the corona from the sun, or the sun's atmosphere.

But this is always changing since the moon is moving away from the Earth about 3 inches per year. Eventually, the umbra will be huge and more people will be able to witness the event. Those lucky bastards in the year 5000 won't have to take special eclipse tours to see one.

We are very lucky to have the moon, or Luna, as the Romans called it. It is the only moon in our solar system that has the largest relative size to its host planet. Contrasting Neptune, Saturn, and Jupiter, they are extraordinarily huge compared to the dots that orbit around them. The moon gives us tides, stable weather patterns, and for millennia, was used as a time piece. Without it, life on Earth would be very different- if it could exist at all. It was only recently (mid 1970's) that we sorta-kinda knew how it ended up in Earth's orbit.

For centuries people speculated that the Earth and the moon were formed together about 4.5 billion years ago as our solar system gathered the dust and debris from a long ago star that went supernova. As our sun horded the 99% of the debris, the rest of the planets had to make due with what was left over. Luckily there was enough to make the 8 planets and 3 dozen or so moons that exist in our solar system today. People though the moon actually broke off from the Earth which would explain its size and close orbit. But when the Apollo missions returned with the 45 pounds of sample from the moon, the rocks told a different story. Although the isotopes of some of the elements were the same as the Earth, like oxygen, the iron content was grossly different. BFD, you say? Well, it is because the Earth has a nickel iron core and if the moon sprouted from the Earth then it would have the same materials. But it didn't.

Another theory, purposed by a Navy officer stationed in Mare Island, CA who had a lot of time on his hands, said that the Earth snagged the moon out of a close orbit and captured it into our own. This theory was accepted from about 1908 until the mid 70's but it had a few holes. The Earth just didn't have enough mass or gravity to pull something as big as the moon into its orbit. A group of astronomers created a computer model that showed that it was possible for an object about the size of Mars to have slammed into the Earth when it was still a molten blob of matter early in the solar system's life cycle. The collision created debris that was pulled into Earth's orbit and that debris eventually formed the moon. After a day or two, the Earth resumed its circular shape and after a few million years or so finally hardened. This would explain the differences in mineral content but even this theory has a few holes that most astronomers and scientists are willing to forgo until a more plausible theory comes along.

Although interest in the moon declined sharply after the last Apollo mission in the early 70's, the U.S. plans on making a permanent station on the moon for research and to have a better launch point for our eventual trip to Mars. Even China has lofty goals of reaching the moon so that the starving people who live there can look up and know that at least a few astronauts who make more than $2 a day made it to the big time. But for now, we Earthlings will be content with making an occasional glance into the night sky to see our closest cosmic neighbor who has been watching our backyard for billions of years.

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