CHAPTER XLII
METEORS AND SHOOTING STARS
"Falling stars," or "shooting stars," have been familiar sights in all ages of the world, but the ancient philosophers thought them scarcely worthy of notice. According to Aristotle they were mere nothings of the upper atmosphere, of no more account than the general happenings of the weather. But about the end of the eighteenth century and the beginning of the nineteenth the insufficiency of this view began to be fully recognized, and interplanetary space was conceived as tenanted by shoals of moving bodies exceedingly small in mass and dimension as compared with the planets.
Millions of these bodies are all the time in collision with the outlying regions of our atmosphere; and by their impact upon it and their friction in passing swiftly through it, they become heated to incandescence, thus creating the luminous appearances commonly known as shooting stars. For the most part they are consumed or dissipated in vapor before reaching the solid surface of the earth; but occasionally a luminous cloud or streak is left glowing in the wake of a large meteor, which sometimes remains visible for half an hour after the passage of the meteor itself. These mistlike clouds projected upon the dark sky have been especially studied by Trowbridge of Columbia University.
Many more meteors are seen during the morning hours, say from four to six, than at any other nightly period of equal length, because the visible sky is at that time nearly centered around the general direction toward which the earth is moving in its orbit round the sun; so that the number of meteors that would fall upon the earth if at rest is increased by those which the earth overtakes by its own motion. Also from January to July while the earth is traveling from perihelion to aphelion, fewer meteors are seen than in the last half of the year; but this is chiefly because of the rich showers encountered in August and November.
Although the descent of meteoric bodies from the sky was pretty generally discredited until early in the nineteenth century, such falls had nevertheless been recorded from very early times. They were usually regarded as prodigies or miracles, and such stones were commonly objects of worship among ancient peoples. For example, the Phrygian Stone, known as the "Diana of the Ephesians which fell down from Jupiter," was a famous stone built into the Kaaba at Mecca, and even to-day it is revered by Mohammedans as a holy relic. Perhaps the earliest known meteoric fall is that historically recorded in the Parian Chronicle as having occurred in the island of Crete, B. C. 1478. Also in the imperial museum of Petrograd is the Pallas or Krasnoiarsk iron, perhaps three-quarters of a ton in weight, found in 1772 by Pallas, the famous traveler, at Krasnoiarsk, Siberia.
But a fall of meteoric stones that chanced upon the department of Orne, France, in 1805, led to a critical investigation by Biot, the distinguished physicist and academician. According to his report a violent explosion in the neighborhood of L'Aigle had been heard for a distance of seventy-five miles around, and lasting five or six minutes, about 1 P. M. on Tuesday, April 26. From several adjoining towns a rapidly moving fireball had been seen in a sky generally clear, and there was absolutely no room for doubt that on the same day many stones fell in the neighborhood of L'Aigle. Biot estimated their number between two and three thousand, and they were scattered over an elliptical area more than six miles long, and two and a half miles broad. Thenceforward the descent of meteoric matter from outer space upon the earth has been recognized as an unquestioned fact.
The origin of these bodies being cosmic, meteors may be expected to fall upon the earth without reference to latitude, or season, or day and night, or weather. On entering our upper atmosphere their temperature must be that of space, many hundred degrees below zero; and their velocities range from ten miles per second upward. But atmospheric resistance to their flight is so great that their velocity is quickly reduced: at ground impact it does not exceed a few hundred feet per second. On January 1, 1869, several meteoric stones fell on ice only a few inches thick in Sweden, rebounding without either breaking through the ice or being themselves fractured.
Naturally the flight of a meteor through the atmosphere will be only a few seconds in duration, and owing to the sudden reduction of velocity, it will continue to be luminous throughout only the upper part of its course. Visibility generally begins at an elevation of about seventy miles, and ends at perhaps half that altitude.
What is the origin of meteors? Theories there are in great abundance: that they come from the sun, that they come from the moon, that they come from the earth in past ages as a result of volcanic action, and so on. But there are many difficulties in the way of acceptance of these and several other theories. That all meteors were originally parts of cometary masses is however a theory that may be accepted without much hesitation.
Comets have been known to disintegrate. Biela's comet even disappeared entirely, so that during a shower of Biela meteors in November, 1885, an actual fragment of the lost comet fell upon the earth, at Mazapil, Mexico. And as the Bielid meteors encounter the earth with the relatively low velocity of ten miles a second, we may expect to capture other fragments in the future. Numerous observers saw the weird disintegration of the nucleus of the great comet of 1882, well recognized as a member of the family of the comet of 1843. As these comets are fellow voyagers through space along the same orbit, probably all five members of the family, with perhaps others, were originally a single comet of unparalleled magnitude.