Comet

Well, that took a long time to read! Learned a lot of stuff I promptly forgot again (just like in school!). It was especially interesting to compare a scientist's hopes for the future from decades ago to what has actually developed. Interesting, and depressing and sad. But also very cool in a lot of ways. ( )

From the basics of what a comet is, to the records of comets seen throughout human history, to the incorporation of comets in myth and legend, and then the hard science of what comets are actually made out of and where they come from, Comet will teach you everything you ever wanted to know about its subject, and then some.

Comet opens with a detailed description of what one would encounter if one could, hypothetically, ride on a comet as it makes its journey through space. The book then goes on to discuss how humanity has viewed the apparition of comets throughout history (usually as a portent of doom.) There is an entire chapter dedicated to Edmund Halley, the friend and contemporary of Sir Isaac Newton, who did so much to further our scientific understanding of comets, and lays out not just his theories and discoveries, but much interesting biographical information as well.

I learned so much about comets that I had never known before. For example, I had never heard of the Oort Cloud, which is a "great spherical assemblage of comets" which surrounds the Sun at a distance of 100,000 AU (Astronomical Units).

A Cometary Bestiary provides reproductions of many illustrations and photographs of different comets seen from Earth throughout human history, and posits the interesting theory that the swastika (an ancient good luck symbol found miraculously throughout the ancient world, before the Nazis ruined it for everybody during World War II) may have been ancient man's attempt at recording the sight of a spectacular comet.

"How does the same curious symbol became established in the ancient cultures of India, China, the American Southwest, Mayan Mexico, Brazil, Britain, and Turkey, among others? The swastika was in general use in Bronze Age Europe from the Arctic to the Mediterranean, spreading in the Iron Age, to the Etruscan, Mycenaean, Trojan and Hittite civilizations... Looking over the entire prehistoric world, we find the swastika used on small and comparatively insignificant objects... and frequently on statues, altars, and the like..."(p. 182)

The text includes a reproduction of a silk scroll from third or fourth century BCE China, the Mawangdui silk, which shows diagrams of comets witnessed by the ancient Chinese. It's all incredibly fascinating, and Sagan masterfully weaves human history in alongside the hard science.

There is also a very interesting chapter on how the cometary impact that wiped out the dinosaurs led to human evolution, thus making comets quite responsible for humanity! This then leads into a chapter on the several periods of mass extinction which have occurred on the Earth every 30 million years or so, and the proposed theories about what might cause this grim phenomena.

"You look at the age of fossils and craters on Earth, and you find a time scale of almost 30 million years. You look at the Sun bobbing in the Galaxy and you find another time scale of roughly 30 million years. It's hard not to think that the two periods might be related, that the oscillation [of the Sun] causes the extinctions." (p.299)

Another theory proposes that our Sun might have an invisible companion star, as most other stars do. "Suppose there was a companion star on a very long elliptical orbit - so that, on average, it was 90,000 AU away, 1.4 light-years. But once each orbit it comes much closer to the Sun, maybe 10,000 AU or even a little closer. This would bring the star into the inner part of the Oort Cloud, where comets are not ordinarily jostled by passing stars. With such an orbit, once every 30 million years the companion would plow through the denser parts of the Oort Cloud, and shower the Earth and neighboring words with comets." (p.301)

These are, of course, just theories, as Sagan is quick to stress, but they make for interesting reading just the same. All in all, Comet is a ferociously interesting book. Sagan's writing is fluid and engaging, easy to read, yet at the same time detailed and informative. Some readers may find certain chapters more interesting than others, depending if their interests run more towards human history or science, but there should be enough of interest to satisfy a diverse group of readers, and it will certainly leave anyone with a lot to think about. ( )

Sagan and Druyan cover pretty much everything you'd ever want to know about comets in their usual inimitable style. ( )

Sagan, along with co-writer Ann Druyan takes a look at what comets are, where they come from, and how they affect things around them.

They also speculate on the possible and actual effects that comets have had throughout history physically, as well as culturally.

http://freesf.strandedinoz.com/wordpress/2012/04/comet-carl-sagan/ ( )