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Comets: From Doomsayers to Delights (Part 1)
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There are two long-haired types headed our way. They go by the code names C/2001 Q4 and C/2002 T7. If you know where to look you can see them now, with a little help. By next month just about everyone on Earth should be able to see the two. Had enough of these apocalyptic riddles?
I'm talking about comets, those rare and beautiful solar system objects, predictable to an extreme in their orbits, but very impulsive as to how they will actually present themselves.
We have two debutantes headed our way in late April and May. The big question is: Will this spring's gossamered guests power through the skies, graced by millions-of-miles-long tails, or will they be tiny, dim, disappointing fuzzballs?
In the coming weeks here we'll look at the historical role of comets as portents of ruin, where they come from and why they do the things they do, and the details of our latest two mentioned above and what to look for as they pass by.
In
order to understand the importance of comets in history you'll have to
put yourself back in ancient times. To most of our ancestors the sky was
a thing of steadiness and relative calm. The stars kept their positions
in the sky year after year after year. The planets, of course, were known
to be the wanderers. But even their movements were relatively predictable.
The reliability of the sky was so well trusted one could set his or her
watch by it. As a matter of fact, social, religious, and agricultural
calendars were set by the movements of the trusted heavens.
So imagine the trepidation when one of these rogues would suddenly come flying by. Here they are, showing up whenever they want, coming from and leaving into whatever direction they choose. They never go by with the same steady motion through the sky, oh no! They come in slowly, speed up as they fly through the starry background, only to slow again ... and then disappear!
Since many people believed the skies were where the Deity or deities resided, many saw comets as messages from above. And almost exclusively it was bad news that was being sent.
Whether one was Chinese, Babylonian, Greek, or Roman, comets meant the death of a king, an impending war, famine, or the end of a dynasty. They were (cue dramatic music) Portents of Doom!
Not everyone saw them as starry harbingers of disaster, even if they couldn't figure out exactly what they were. The philosopher Aristotle had his spin on these strange visitors. The Universe According to Aristotle portrayed the universe as perfection. All the different heavenly objects traveled through the perfect heavens with perfect motions.
So how did Aristotle explain the creepiness of comets? They were an atmospheric phenomenon, not a heavenly one! They were literally in the blue skies above our head. This view was held for another 2000 years until Edmund Halley put a final nail in old ultra-influential Aristotle's coffin.
Halley was a contemporary and friend of Isaac Newton in the late 17th century. Newton had recently shown that there were laws governing the motions of the universe. Might comets just be solar system bodies, no better or worse than planets and moons? Could Newton's laws be used to predict whether a comet might actually return?
Looking back at historical records Halley discovered that the comet of 1682 had some unique characteristics, making it slightly unusual even by comet standards. Looking back farther he saw that the comet of 1607 and one way back in 1531 were also very similar to the 1682 comet. Hmmmm ...
Was it too much to expect that all three might be the same animal? Using Newton's laws of motion and putting his reputation on the line, Halley predicted the return of that comet "about the end of the year 1758, or the beginning of the next."
Lo and behold! On Christmas Day 1758, a farmer in Dresden first spotted the returning comet. It has returned several times since, the latest visit being in 1986.
Newton's laws stood the test, Aristotle was finally laid to rest, and the now famous comet was named Halley's Comet. Comets, it turned out, were just another group in the family of the sun, and like the other bodies were subject to ordinary laws of motion. But what were they? Where were they coming from? And why the tail?
Tune in next time as we continue our look into comets and what makes them tick.
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2004.04.18 12:38 PM | Comments (0)
