Saturday, 22 December 2007

Comets, Meteors and Shooting Stars

Comets, Meteors and Shooting Stars


From American Boy, January 1912, digital copy 2007 by Doug Frizzle

IT IS rather hard to draw the line between comets, meteors and shooting stars, and even astronomers are at something of a loss to furnish hard and fast rules to distinguish them. As a, rule, comets are mainly composed of gas or gaseous matter, and travel in a regular course or orbit, while meteors or "shooting stars" are composed of metallic or stony material and have no real defined orbit.

Certain meteors or meteoric showers have regular orbits, however, and in some cases these meteoric showers are believed to be the remains of comets which have been split up or otherwise disintegrated. This is fairly well proven by the fact that the present meteors follow practically the same course and appear at the same time that missing comets should. The Brooks comet is pretty well known to be composed of gases, but even so, these gases might readily be solidified or combined with other matter and form solid material under certain conditions. Little is really actually known of the formation or composition of these celestial bodies, for while some observers claim a comet to be entirely gaseous, others equally as competent insist that the same comet is composed of great numbers of small meteors, while others claim that the head is solid and the tall gaseous. A great many comets have been recognized for many years and their orbits and the time of their appearance is well known and is computed for years in advance of their arrival. Such is the case with Halley's comet and many others.

Meteors are rather erratic and while certain seasons of the year are more productive of meteors than others, owing to the earth's passage through belts of meteoric showers, yet they are visible at all times and on any bright, clear night meteors or "shooting stars" may be seen.

The great majority of shooting stars never reach the earth but are entirely consumed while passing through the outermost stratas of our atmosphere. Doubtless many more fall into the sea and are never seen. Many people have seen meteors so brilliant and apparently so close at hand that they have actually thought they saw the spot where they fell, but authentic cases of eye witnesses of a meteor striking the earth are very rare.

Several years ago, while in the West Indies, I was fortunate enough to witness two exceedingly brilliant meteors. The first of these fell at midday and although it was a bright sunny day the light was so intense that it seemed like a magnesium flashlight. The meteor caused a sound like escaping steam and exploded with a deafening detonation. It was seen to fall into the Carribean Sea some ten miles distant and the splash of water was plainly visible.

The other meteor fell at night and for several seconds the atmosphere was illuminated with a greenish light as brilliant as day. The report of this bursting meteor was as loud as a large cannon and the natives screamed and ran in every direction believing that one of the island's volcanoes was in eruption. At the time we thought this meteor struck close at hand but a few days later the captain of a steamer told me that he had seen the same meteor some three hundred miles distant and that it appeared just as brilliant and exploded with as loud a report as described by us so that it was evident that it might well have struck several hundred miles from either of us, Meteors are roughly divided into two classes: stony meteorites and metallic meteorites. The first of these are stony and usually bear a general resemblance to trap rock, although usually more rounded and showing evidences of recent fusion. The metallic meteorites are composed mainly of nickel-iron and are very heavy. They are usually dull blackish or rusty on the outside with numerous rounded or smoothed nodules and hollows on their surface. In section they present curiously formed patterns known as Widmanstatten Figures and the presence of these are a sure proof of the meteoric origin of the specimen.

Many rare minerals and metals are found in meteorites and they are invariably of great interest to scientists.

While small meteorites frequently strike the earth, yet they are usually of great value, for no two are just alike in structure or composition. In some places, as in certain districts in Iowa, meteorites are quite common and as a rule these visitors from the heavens are far commoner on level, treeless plains than in wooded districts; not because more have fallen there but because they are easier to see or find. Very large meteorites are rare but quite a number have been found. Among these large specimens is one in the Yale museum weighing several hundred pounds and the huge specimens in the American Museum of New York City which were brought from Greenland by Commander Perry.

Doubtless most of the smaller specimens are but fragments from larger bodies which exploded upon coming in contact with the earth's atmosphere, and there seems no real reason why enormous meteors, or aggregations of small ones, should not strike the earth at any time or place. Such things have occurred in the past and at least one such happening has left indisputable records of the enormous size and power of large meteors. When this huge aerolite struck, or what its size, may never be known, but the impact was sufficient to form a great depression, or basin, in the crust of the earth that for many years was considered a volcanic crater. Coon Mountain, or Coon Butte is the common name of this crater but it is now known also as Meteor Crater. It is situated in northern central Arizona and investigations by trustworthy geologists and scientists have proven beyond a doubt that it was formed by the blow from a gigantic meteor, or aerial projectile of some sort.

The country around Meteor Crater is a fairly level, rocky plain with a thin covering of soil, in spots the soil is entirely absent while there are no trees upon the plain other than stunted cedars and a sparse growth of cottonwoods and walnuts along the water courses. There are no volcanic rocks of any sort nearer than Sunset Mountain, nine miles distant, and the San Francisco Mountains forty miles to the northwest. The crater iiself is nearly circular and is about 4,000 feet, or about three-fourths of a mile in diameter. From the rim to the interior central plain or floor it is about 570 feet deep.

The rim is formed of broken and pulverized rock which has been forced up from beneath the surface of the earth and careful observations and measurements, as well as comparisons of the rock in the rim and samples of the original strata obtained by drilling, prove that this enormous mass of solid rock has actually been lifted upward for more than one hundred feet. The weight of this lifted mass of rock is estimated at twenty to thirty million tons and the fragments are of all sizes from the finest gravel to masses weighing over four hundred tons.

The total amount of material which was forced out to form the crater is over three hundred million tons. With such startling figures it is next to impossible to estimate the size of the projectile which caused the upheaval, or to even guess at the speed with which it travelled or the energy it exerted, but it is safe to say that it weighed at least a million tons and travelled far faster than a rifle ball. It certainly was several hundred feet in diameter and may have been either a solid meteorite or a dense mass of innumerable smaller projectiles.

That the present floor of the crater is composed largely of accumulated debris seems certain, for borings have shown similar material to extend down some five or six hundred feet. An Iron Company has a plant in the centre of the crater and large quantities of nickel iron (meteoric iron) have been collected both from the surface and from drillings.

Although several thousand tons of this material have been gathered, yet the great bulk, at least 90 per cent, of the original meteor remains to be accounted for. Several theories have been advanced to solve this puzzle, some of which are rather far-fetched. Among these is the theory that the mass, after striking, rebounded into space or else bounded into the Pacific Ocean.

These theories are unworthy of notice and the only ones worthy of consideration are the following: First that the huge mass was broken into small pieces and thrown out of the crater by the rebound of its own force. Second: That it has disappeared through oxidization and decomposition. Third: That it is still somewhere and in some form in the depths of the earth within the crater. The first two of these theories seem to have been disproved by the facts that there have been very few, if any, fragments of the meteoric mass found on the plains around the crater and that all the meteoric material found in the crater is in a fine state of preservation and shows little sign of oxidization.

This brings about the conclusion that a vast mass of meteoric iron lies somewhere beneath the crater but how far it penetrated or where or when it will be found, remains a mystery which will be of the greatest scientific interest when solved.

The human mind can scarcely grasp the size and power of the rushing meteor which, travelling at a rate of from twenty to thirty miles a second, struck the rocky Arizona plain with sufficient force to tear out a great bowl-shaped crater nearly a mile in diameter and a thousand feet deep and hurled up three hundred million tons of rock and sand, tossing great masses of four hundred tons far out upon the plain and pulverizing the flinty quartz to the finest flour. It is by far the most stupendous "shooting star" of which we have any record and the crater is undoubtedly the most remarkable mountain in the world and instead of being devoted to the commercial uses of an iron company it should be guarded and preserved by the Government as the most remarkable and most interesting of our natural curiosities.

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As an armed forces brat, we lived in Rockcliff (Ottawa), Namao (Edmonton), Southport (Portage La Prairie), Manitoba, and Dad retired to St. Margaret's Bay, NS.
Working with the Federal Govenment for 25 years, Canadian Hydrographic Service, mostly. Now married to Gail Kelly, with two grown children, Luke and Denyse. Retired to my woodlot at Stillwater Lake, NS, on the rainy days I study the life and work of A. Hyatt Verrill 1871-1954.