Chapter III: Preface: 5 (2)

While the term “convection” may not be familiar, the role convection plays in filling the sky with beautiful clouds on a hot summer’s day is well known. Such cloud formation results from convection in the gaseous free atmosphere. Much more remarkable and regular are the results of _controlled_ convection in layers of _liquids_ rather than gases. Laboratory investigation of the effects produced by convection processes in heated liquids formed the basis for Wasiutynski’s new theory.

According to this theory, convection processes in the only partially solidified outer shell of the youthful moon could have given rise to great numbers of surface features having the size, shape, and distribution of the common lunar craters. In far more satisfactory fashion than any other theory so far proposed, the convection-current hypothesis of Wasiutynski explains the many and distinctive characteristics of the non-ray craters on the moon.

RECOGNIZED METEORITE CRATERS OF THE WORLD

NAME LOCATION DATE OF
RECOGNITION

Canyon Diablo Coconino County, Arizona 1905
Odessa Ector County, Texas 1929
Henbury McDonnell Ranges, Central 1932
Australia
Wabar Rub’ al Khali, Arabia 1932
Campo del Cielo Gran Chaco, Argentina 1933
[2]Haviland (Brenham) Kiowa County, Kansas 1933
Mount Darwin Tasmania 1933
[3]Podkamennaya Tunguska Yeniseisk District, Siberia 1933
Box Hole Station Plenty River, Central 1937
Australia
Kaalijarv Oesel, Estonia 1937
Dalgaranga Western Australia 1938
Ussuri (Sikhote-Alin) Eastern Siberia 1947
Wolf Creek Wyndham, Kimberley, 1948
Western Australia
Aouelloul Adrar, Western Sahara 1952

5. HEAVEN KNOWS WHERE OR WHEN

Meteorites have been falling upon our planet for a long time—how long, it is hard to say with accuracy. Up to now, no specimens certainly identified as meteorites have been found in ancient rock layers. Scientists have been able, however, to estimate the age of several meteorite craters on the basis of the degree of weathering not only of the crater rims, but also of the meteorites found around the craters. Age estimates have also been based on the ages of fossils found in silted-up crater interiors and on other related indirect evidence.

As we have already noted, the Canyon Diablo, Arizona, crater is thought to be 20,000 to 70,000 years old. The Odessa, Texas, crater is at least 200,000 years old; and the Haviland (Brenham), Kansas, craters more than 600,000 years old. Clearly, meteorite falls have been occurring over a very long period of earth history.

For many years, scientists have studied the distribution of recovered meteorites around the world in an effort to find out whether there are any places on the land surface of our globe where meteorites have fallen in unusually large numbers.

The idea that any particular spot on the land surface of the earth might in some way attract more meteorites to it than other locations seems unreasonable because of the very nature of the target presented by our planet to the meteorites wandering through space. Not only is the earth in motion, but it is in very complicated motion. Our earth revolves about a sun which is also in motion through space. At the same time, the earth is rotating on its axis. A single point on the surface of the earth therefore traces a very erratic path in space with the passage of the years, and the likelihood that this particular point would be struck by more than one meteorite (if indeed by one!) must be very small.

Studies have shown that the people of the earth have a great deal more to do with “concentrations” of meteorite recoveries than anything else. _Population density_ is the first important factor. Clearly, the more people living in a given area, the higher the probability that a meteorite fall will be seen and reported and that the fallen mass itself will be recovered. A prime example is India, one of the most densely populated regions of the world. Of the 102 meteorites recovered in that country up to 1953, 97 were of witnessed fall. This extremely high proportion of falls is undoubtedly due to the fact that for centuries such an event could hardly have taken place in that country without attracting the attention of large numbers of people. Apparently, the majority of Indian meteorites have been recovered as they fell, for only 5 unwitnessed falls are recorded for that country.

On the other hand, from French West Africa only 5 falls and 3 finds have been reported throughout an area slightly larger even than India’s. This country thus provides an example of a sparsely populated region, in many provinces of which a meteorite fall might pass unobserved, and a fallen meteorite might remain undiscovered.

A second factor is the _degree of civilization_ reached by the inhabitants of a particular area. Those regions of the world which have been settled the longest and which have seen the development of the higher cultures will be the most likely to support a populace that will take an interest in and report the occurrences of natural events like meteorite falls. Such a populace will also be more likely to bring suspected meteorites to the attention of experts.

For example, up to 1953, 55 witnessed falls and 3 unwitnessed falls were known from France, a country of relatively small area, but with a high population density and an advanced degree of civilization. From the whole vast area of Siberia, on the other hand, only 20 meteorite falls and 23 finds have been reported during the same interval.

In the past, scientists have suggested that various natural forces, such as the magnetic field of the earth or the attraction of high and massive mountain ranges, might cause more meteorites to fall in one place than another. But all available evidence indicates that this is not the case. The fall of meteorites upon the earth has been and is a process that shows no apparent pattern. Only “human” factors (like population density and scientific interest in meteorites) can be considered as accounting for any concentrations of meteorite falls in particular regions or countries.

In historic times, the number of man-built structures (houses, barns, hotels, office buildings, etc.) has increased tremendously. Such structures have presented an ever-expanding target to hits by falling meteorites. On pages 73, 74 is a listing of some of the meteorites that have struck and damaged buildings during the last 150 years or so. The items included in this list were chosen on the basis of interest, authenticity, and concreteness of detail.

The stories of all these meteorite falls are exciting, but none more so, perhaps, than that of the Beddgelert, North Wales, stone. This meteorite fell in the small hours of the morning on September 21, 1949. Not many people saw the fireball that accompanied its descent because of the early hour (1:45 a.m.), but one of the few persons who happened to be outside said that it resembled a huge rocket as it flashed across the sky. He also reported that the appearance of the fireball nearly frightened the swans in the local park to death, the birds fleeing in all directions.

The manager of one of the hotels in Beddgelert simultaneously was awakened from a sound sleep by the barking of his dog. This was an unusual occurrence, and the man was surprised by it. While he was trying to account for the dog’s peculiar behavior, he suddenly realized that something quite out of the ordinary was happening outside. He heard a series of unevenly spaced bangs that he later compared to “a naval broadside.” But as the noise died away and nothing further happened, he went back to sleep.

About noon on the next day, the manager’s wife went into the upstairs lounge of the hotel, a room right under a part of the roof. She was astonished to find plaster dust all over the floor. It had obviously come from a jagged hole in the ceiling. And, on the floor, she found an odd-looking dark stone.

Investigation showed that this stone had indeed fallen through the roof. It had made a neat round hole in four overlapping thicknesses of slate, shattered the underlying lath, made a dent in the lower edge of an H-section iron girder, and had finally broken through the plaster ceiling into the hotel’s upstairs lounge.

Although it was clear that the stone had come through the roof, the hotel manager did not connect the event in any way with the peculiar noises he had heard during the preceding night.

He tried to cut the stone on an emery wheel, but it was too hard.

That evening, an old miner in the hotel restaurant recognized the stone as a meteorite. Many years before, he had visited a museum and had seen specimens of meteorites on display there.

The slabs of slate penetrated by the meteorite would have provided good evidence as to the speed of the cosmic missile at the time it struck the roof. But, unfortunately, these appear to have been thrown away at the time the roof was repaired. This fact is mentioned to show that important scientific evidence is sometimes unwittingly destroyed before investigators can get a chance to examine it.

Along with the rapid increase in the number of man-made buildings has, of course, gone a simultaneous increase in the world’s population itself. A person does not present as large a target to a falling meteorite as a house or barn, but even so, if there were enough people on the earth, it would seem that someone was bound to be hit sooner or later.

Actually, the first _authentic_ case of a person being struck by a meteorite did not occur until November 30, 1954. Even then, the hit was an indirect one. At Sylacauga, Alabama, a meteorite fell through the roof of a house, went through the ceiling of the living room, struck the top of a radio, and—bouncing in a 6-foot arc—hit the lady of the house, who was taking a nap on the couch. Fortunately, nearly all of the energy of the meteorite was spent by the time it struck the woman, and, moreover, she was covered with two heavy quilts so that she was not critically injured. But she did receive bruises serious enough to send her to the hospital.

The instances just given show that a number of meteorites have struck buildings and, in one case, a cosmic missile has hit a human being. Nevertheless, such events are really quite rare. In fact, mathematical calculations indicate that, on the average, we can expect one meteorite to fall per township (36 square miles) per 1000 years. A rate like this does not justify the loss of any sleep over the possibility that you might some time be hit by a falling meteorite!

SELECTED LIST OF METEORITES THAT HAVE STRUCK AND DAMAGED BUILDINGS

NAME AND LOCATION TYPE APPROXIMATE WEIGHT YEAR

Baxter, Missouri stone 611 gm.[4] 1916
Meteorite penetrated roof and struck a log joist, which checked the fall.
The stone lodged in the attic.
Beddgelert, North Wales stone 794 gm. 1949
Meteorite made a clean hole through 4 thicknesses of slate roof. It then
shattered underlying wood, made tiny dent in bottom edge of H-section iron
girder, and broke through plaster ceiling into hotel lounge below.
Benld, Illinois stone 1770 gm. 1938
Meteorite penetrated garage roof, top of car, and seat cushion. It struck
and put 1-inch dent in muffler, then bounded back up and became entangled
in seat cushion springs.
Bethlehem, New York stone 11 gm. 1859
Meteorite struck the side of wagon house, bounded off, hit log upon ground,
bounded again, and rolled into the grass. (A dog lying in the doorway of
the wagon house jumped up, ran out and seized the meteorite, but dropped it
right away, probably because of the warmth and sulfurous odor of the stone.)
Branau, Bohemia iron 19,000 gm. 1847
Meteorite penetrated into room where 3 children were sleeping and covered
them with plaster and debris. They were unharmed.
Constantia, South Africa stone 999 gm. 1906
Meteorite penetrated 2 thicknesses of corrugated iron roofing and smashed
ceiling.
Kasamatsu, Japan stone 721 gm. 1938
Meteorite penetrated roof of house and stopped on floor. It went through
roof tile, ⅓-inch wooden roof-panel, and layer of clay 1 inch thick between
them.
Kilbourn, Wisconsin stone 772 gm. 1911
Meteorite went through 3 thicknesses of shingles, a 1-inch hemlock roof
board, and a ⅞-inch hemlock floor board. It then glanced in turn against
the side of a manger and the stone foundation of the barn and finally
penetrated 2½ inches into the clay floor of the barn.
Pantar, Philippine Is. stone shower 1938
Sixteen stones were recovered; thousands “as big as corn and rice grains”
fell on roofs.
Sylacauga, Alabama stone 3863 gm. 1954
Meteorite penetrated composition roof material, ¾-inch wooden decking,
¾-inch wooden ceiling, and interior wallboard. It then hit a radio,
punching a 1-inch hole in plywood top, and bounced 90° towards the east,
striking woman lying on couch.

6. FINDERS FOOLISH, FINDERS WISE

People find a great many meteorites that were not seen to fall. Most of these landed on the surface of the earth at some time in the remote past or happened to fall in an originally unpopulated portion of the land area of the globe. Generally, such meteorites are discovered entirely by accident, although in recent years quite a few recoveries of unwitnessed falls have been made by design. This has been the case during the systematic surveys with meteorite detectors conducted around such recognized meteorite crater areas as Canyon Diablo, Arizona; Odessa, Texas; and Wolf Creek, Australia.

The different modes of discovery of meteorites not seen to fall are interesting in themselves. The largest percentage of finds has unquestionably been made by farmers. The Plymouth, Indiana, meteorite, for example, was plowed up or, as the farmer nursing the rib bruised by his bucking plow would probably prefer to say, “plowed into.” So were such meteorites as the Algoma, Wisconsin; the Bridgewater, North Carolina; the Carlton, Texas; and the Chesterfield, South Carolina, to name only a few. A farmer found the Kenton, Kentucky, iron while he was cleaning out a spring. Another farmer was removing debris from an abandoned water well in an attempt to revive it when he discovered the Richland, Texas, iron. A field drainage project brought the Seeläsgen, Poland, iron to light. A man planting an apple tree near his house dug out the Mount Joy, Pennsylvania, iron, and a farmer hoeing tobacco turned up the Scottsville, Kentucky, iron.

The second largest percentage of finds probably has been made by miners. Prospectors and placer miners have mistaken numerous iron meteorites for lumps of silver ore. Among these are the Murfreesboro, Tennessee; Lick Creek, North Carolina; and Illinois Gulch, Montana, irons. The Aggie Creek, Alaska, iron was raised by a gold dredge. The gold miners recognized this meteorite as an unusual “haul” when it announced its presence by clanging loudly on the metallic screen of the dredge.

Men at work on road construction are also to be thanked for chancing upon meteorites of unwitnessed fall, for example, the irons found by road crews at Bear Lodge, Wyoming, and at Bald Eagle, Pennsylvania.

Some meteorites have been “found twice.” At Opava, Czechoslovakia, archeologists discovered seven pieces of meteoritic iron in a buried Stone Age campsite—the oldest meteorite collection so far on record! Apparently the paleolithic inhabitants of the Opava region had gathered the heavy masses together and used them to bolster the fireplaces in their rude encampment.

Investigators discovered the Mesaverde, Colorado, iron in the Sun Shrine on the north side of the Pipe Shrine House, and the Casas Grandes, Mexico, iron in the middle of a large room of the Montezuma temple ruins, carefully wrapped in linen cloth like a mummy. Members of an early archeological survey found the small Anderson Township, Ohio, meteoritic specimens on altars in mounds of the Little Miami Valley group of prehistoric earthworks. Some scientists believe that the American Indians transported these specimens to Ohio from the site of the Brenham meteorites in Kiowa County, Kansas.

Other modes of discovery fall into no pattern and must be regarded as merely curious. A farmer plowing his field near Pittsburgh, Pennsylvania, came across a snake. In looking for a suitable stone with which to kill it, he first seized upon a mass of iron too heavy to lift. After he had killed the snake with a handy rock, the farmer’s attention was drawn back to the small but remarkably heavy mass he had first tried to pick up. He carted it off to the city, where eventually it was recognized as a meteorite.

In another unusual recovery, fishermen brought the Lake Okeechobee, Florida, stone up from the waters of the lake in a net—the only such recovery recorded in the whole literature of meteoritics, although three-fourths of all meteorites must necessarily fall into water on our ocean-covered globe. Again, the members of the Australasian Antarctic Expedition of 1911-1914 were surprised to find the Adelie Land, Antarctica, stone lying on the snow some 20 miles west of Cape Denison.

Because the true nature of meteorite finds has often been unrecognized—sometimes for many years—these masses have been put to some rather lowly uses. The finder of the Rafrüti, Switzerland, iron meteorite used it as a footwarmer, and many of the heavy irons have been employed as haystack, fence, and barrel-cover weights, or as anvils, nutcrackers, and doorstops.

Some have fared better, as did the 1,375-pound La Caille, France, meteorite, which the people of the village used for two centuries as a seat in front of their church. Others, however, have fared even worse. Blacksmiths and assayers have smelted up and destroyed a number of iron meteorites either in the making of tools (like plowshares, axe-heads, and knife-blades) or in the quest for precious metals. Nearly all of the iron meteorite that was found by the farmer near Pittsburgh was worked up by a blacksmith and lost to science. Even the stone meteorites have occasionally fallen victims to man’s greed for gold. Miners who believed that the 80-pound San Emigdio, California, stony meteorite was gold-bearing mashed it to powder in an ore-crusher.

On the contrary, people who, in one way or another, have become acquainted with the characteristics of meteorites have brought a number of these objects to the attention of scientists. For example, one of the University of Nebraska men who worked on the excavation and removal of the large Furnas County stone meteorite (see Chapter 2) became keenly interested at that time in meteorites in general, and took the trouble to learn as much as he could about them. Several years later, after he had become director of a state park museum in southern Oklahoma, a large metallic mass was reported to him. The finder of this mass of metal had known of its existence for some 20 years, but had never succeeded in getting anyone to examine it carefully. The former field worker took one look at the object and, on the basis of his knowledge of meteorites, concluded that it probably was a huge iron meteorite. He immediately called the Institute of Meteoritics by long distance and was able to give such a wealth of significant details that a field party left at once for the site. In this way, the Lake Murray, Oklahoma, meteorite was identified and recovered.

The unoxidized central core of this iron weighed more than 600 pounds. Before excavation this core was surrounded by a “shell” of oxidized meteoritic material several inches thick, as shown on page 77. Such a shell of oxide clearly indicated that the meteorite had been subjected to weathering in the ground for many thousands of years.

In general, meteorites _seen to fall_—possibly because of the magnitude and impressiveness of the light and sound effects connected with their descent—have received respectful treatment after recovery. Most of them have been presented to men of science for study and eventual display in some museum collection. Even when kept by their finders, the specimens usually have been well cared for. After the fall of the Flows, North Carolina, meteorite in 1849, the owner of the land on which it came down set the stone in a place of honor on top of a barrel fixed to a post. On the post he put up the notice:

“_Gentlemen, sirs—please not to break this rock, which fell from the
skies and weighs 19.5 pounds._”

This landowner obviously realized that nearly everyone has the unfortunate urge to hammer on strange rocks.

Of course, there have been exceptions to the respectful treatment of meteorites seen to fall. The finder of one fragment of the Zhovtnevy Hutor, Russia, fall tossed it into the stove, and a farm woman lost another by throwing it at an unruly horse. A peasant who thought meteorites possessed miraculous powers powdered up a piece of the diamond-bearing Novo-Urei, Russia, stone and ate it!

7. LANDMARKS, SKYMARKS & DETECTORS

The chemist can easily obtain materials for his research work from reliable supply houses. The meteoriticist (as a scientist who studies meteors and meteorites is known), is not this lucky. He must search for the specimens he wishes to investigate wherever they may have landed on the wide, wide earth. This “needle-in-a-haystack” problem could rarely be solved if it were not for certain mathematical and instrumental aids that swing the balance in favor of the meteorite hunter. When meteorites are seen to fall, these aids can be brought into play only if certain information is supplied by eyewitnesses of the falls. For this reason, everyone ought to be acquainted with the facts about meteorite falls that scientists will need to know in order to make finds, and should understand how these facts must be reported in order to be of maximum use to field parties.[5]

The problem of working out the path a fireball has followed in the sky boils down to this. The investigating scientists must be able to fix the position _in space_ of certain important points on the fireball’s path. This idea of fixing points is not really difficult at all. Suppose, to take an analogy from baseball, we have base runners on first and third. These two players are intently watching their team’s clean-up hitter, who is “crowding the plate.” Consequently their lines of sight intersect at home plate and give a very good “fix on” its position, as navigators say. This is the way a fix can be obtained in _two_ dimensions; that is, essentially, in the plane of the earth’s surface.

B. A fix determined in three dimensions. The lines of sight of the
runners on the first and third intersect at x.]

Now, let us move into the _third_ dimension, since a fireball’s path through the atmosphere lies in space, not in the “flat” plane of the earth’s surface. Returning to our baseball diamond, let us suppose that a helicopter with an enterprising photographer aboard hovers over the centerfield bleachers so that he can take pictures of the record crowd. While the umpire is dusting off home plate, the two runners on first and third simultaneously sneak a look to see what the helicopter is doing. Their lines of sight now intersect at the helicopter and fix its position _in space_.

Similarly, the location of a fireball path in space is determined by the fixing of certain points on the luminous streak seen in the sky. Instead of using only two intersecting lines of sight (those of the runners on first and third in our analogy), scientists investigating a meteorite fall try to collect as many different lines of sight as possible from people in the region above which the fireball streaked. The more commonly determined points are those of the fireball’s appearance and disappearance and those where “explosions” took place. These points are generally located by use of the method we have described in some detail above, the so-called _intersecting-lines-of-sight_ method.

The most important point on a fireball path is the point of disappearance. The most valuable single piece of information you can supply about a meteorite fall is as accurate an answer as possible to the question: In what compass direction were you looking when you _last_ saw the fireball? This question has often been twisted around in newspaper and radio accounts into the meaningless question: In what direction was the fireball going when you saw it?

One person cannot give the answer to the second question because from a single station it is impossible to determine the _true_ direction of motion of an object seen in the sky. One person can report only an _apparent_ direction of motion, which is of little or no value in locating the last point on the luminous path, generally referred to as the “end-point.” Therefore, though you cannot by yourself determine the actual direction in which a fireball is _moving_, you can report the direction in which you were _looking_ when you last saw the fireball, that is, due south, southwest, northeast, etc.

Scientists are eager to obtain reliable reports on the compass direction to the fireball’s point of disappearance from as many widely separated eyewitnesses as possible. They then can plot the individual lines of sight on a good map, marking exactly where these lines intersect. In this way, the investigators can make reasonably accurate fixes of the position of the point on the earth’s surface that is situated directly below the end-point of the fireball path, as this end-point was seen in the sky by each pair of eyewitnesses.

Instead of using the ordinary compass direction to a fireball’s point of disappearance, you may prefer, as do astronomers, to use the azimuth. What we have been calling a “compass direction” is one that is expressed in terms of the cardinal points: north, south, east, west. An azimuth is a direction stated in _degrees_. Rough azimuths can be taken with a compass, but for accurate work, a graduated circle, like that on a transit or theodolite, must be used. Astronomical azimuths begin at the _south_ point and continue clockwise full circle to 360°. For example, the lines of sight in the diagram, p. 87, could very well have been given as astronomical azimuths. And, in the diagram, p. 91, the line of sight C₁ could have had the precise designation 118° and C₂ that of 222°.

Every fix serves to guide field parties to areas that are to be carefully searched for fallen meteorites. Extra-thorough searches are made if the people living in a particular area reported that they heard meteorite fragments hissing and whining on their way to earth or heard the thumps of their impacts on the ground.

You will notice that so far we have been treating our problem as a two-dimensional one. We have been working with _directions_ only and have plotted out direction indicators on a map representing the plane of the earth’s surface. Now, as we did in our baseball analogy, let us move into the third dimension.

If, in addition to compass directions to the observed endpoint, scientists can also obtain the apparent _elevation_, in degrees, of this point as seen by the various eyewitnesses, then with the help of a little trigonometry, they can fix the position _in space_ of the end-point itself rather than the position of its _projection_ on the surface of the earth.

This same procedure can be followed in fixing the space-position of any well-observed point on the fireball path. It therefore becomes possible when _both_ elevations and compass directions are reported for several points on the fireball path to determine the flight-path or, as it is technically called, the _trajectory_, of the falling meteorite through the atmosphere. Trajectory determinations are of great scientific value.

You can estimate the compass directions and elevations to the important points on a meteorite trajectory at the actual time of fall. Or you can have the scientific field party make or check your measurement at some later time by setting up a surveying instrument at the very point from which you saw the fireball.

The accuracy of your measurements can be improved if you have been able to “line up” the point, L, at which you saw the fireball disappear, with some familiar object on the horizon, such as a church steeple, a tall tree, a telephone pole, or a lightning rod on a farm building. You will recall that an eleven-year old girl provided one of the field parties from the Institute of Meteoritics with an excellent observation of the point of disappearance of the Norton fireball. She was able to do this because she remembered just where it went out of sight behind a familiar landmark.

O₁ First observer.
A₁ Apparent height of point of disappearance (50°).
C₁ Compass direction of point of disappearance (N 62° W).
O₂ Second observer.
A₂ Apparent height of point of disappearance (45°).
C₂ Compass direction of point of disappearance (N 42° E).]

If the fall occurs at night, you can help investigators greatly if you are familiar enough with the brighter stars to use them as “skymarks.” You simply note as quickly and sharply as you can just where the fireball path was in reference to those prominent stars. This alert observation of yours will at least be a great aid to investigators who are searching for meteorites that may have fallen from the fireball; and, moreover, there is no telling what else your quick eye might have captured for science.

While looking through a window, Kayser, the Polish astronomer, saw a fireball appear at Rigel and move to Sirius, where it disappeared. This observation of his proved to be one of the most accurate and _significant_ ever made of the fall of a meteorite. For it enabled the German mathematician, Galle, to show that the Pultusk meteorite, which produced the fireball Kayser saw, came into the Solar System from interstellar space!

It is very essential to carefully notice and mark the exact spot from which your observation was made so that you can return to it if scientists wish to set up surveying instruments there.

The map and side view of the Norton County, Kansas, meteorite trajectory show the practical results that the Institute obtained by use of the intersecting-lines-of-sight method. The fireball accompanying the Norton meteorite fall appeared at A. The first “explosion” took place at E₁, the second at E₂, and the fireball disappeared at L.

If markers were dropped straight down to earth from each point along the trajectory or flight-path of a meteorite through the atmosphere, the line joining the points where the markers fell would be the _earth-trace_ of this trajectory. The directions of sight to these various points are indicated for people living in the towns along and near the earth-trace of the Norton meteorite fall. The solid-line arrows represent the direction of the point of disappearance; the dotted-line arrows, the point of appearance; the dash-dot arrows, E₁; and the dashed arrows, E₂. The probable area of fall is shown as an oval-shaped area, the longer axis of which is identical with the direction of motion of the meteorite.

The many fragments of all sizes recovered from the Norton fall were all found within the bounds of this oval-shaped area, although unavoidable errors of observation placed the center of the oval about 4 miles too far to the north.

In addition to the questions about direction and elevation, there are a few more that investigators of meteorite falls would like to have observers answer.

At what time (determined as accurately as possible) did the fall
occur? Knowledge of this time is necessary if the path in which the
meteorite was moving about the sun is to be calculated by scientists.

Did you hear any sounds, either while you were watching the fireball
or after it disappeared? If you heard such sounds as the whining or
hissing of meteorite fragments flying through the air or the heavy
thumps of their impacts on the earth, then you were very close to
where the meteorite came down!

How many minutes and seconds (again determined as accurately as you
can) passed between the time when you saw the fireball vanish and the
instant when you first heard sounds from it? Such sound data permit
rough determination of the distance from the observer to the point
where the meteorite fell.

How long did the sounds set up by the meteorite last, and in what
direction did these sounds seem to die out?

If you or your neighbors find fragments that you suspect are pieces of the meteorite, these specimens should be shown to the investigating field parties at once—preferably undisturbed and in the very places where they fell. In any event, the suspect masses should not be hammered on and broken up! Even as late as 1958 in a country as science-conscious as Germany, a beautiful stony meteorite, seen to fall and speedily found by an alert group of children playing out of doors, was deliberately broken up into 5 pieces in order that each of the children (aged 9 years and up) might take home a “souvenir” of the event. Later, these pieces had to be laboriously reassembled by scientists before any idea could be gained of the original shape and surface features of the meteorite.

Even when thorough searches are made, not all the meteorite fragments in the area of fall may be found for many months. But if the people living in the region have been alerted and are on the lookout for unusual specimens or signs of meteoritic impact (such as freshly made holes or “craters” in the ground, shattered tree limbs, and so forth), the chances of ultimately finding many or most of the fallen masses are good.

As we have already mentioned, numerous fragments of the Norton meteorite (including one weighing 130 pounds) were found within two to three months after its fall on February 18, 1948. But the main mass was not discovered until the following August, when a caterpillar tractor nearly tipped over into the large impact funnel that this huge stone had made in the earth. Fortunately, field searchers from the Institute had already talked to one of the farmers using the tractor and had told him that just such a “crater” might be found in the very area under cultivation. Consequently, the crater was promptly reported.

In surveys concerned with the location and recovery of meteorites _not_ seen to fall, we find that sometimes meteorite fragments, particularly the smaller ones, lie on the surface of the ground or at shallow depth. Such fragments were probably too light to penetrate deep into the ground or, in the years since their fall, the action of rain, wind, and frost has uncovered them.

In such cases, a party of searchers generally spreads out in order to get over as much ground as possible and each member of the group looks for meteorite specimens without using instrumental aids. Visual searches of this type have been very successful, for example, around the Canyon Diablo crater, where almost the entire plain out to several miles from the rim once was sprinkled with large and small fragments of meteoritic nickel-iron. This type of meteorite hunt is of only limited effectiveness because the specimens (or at least a part of each one) must be visible to the searchers.

To increase recoveries, searchers have employed, in addition to their eyes, various types of permanent magnets, either mounted on the end of a cane and used to probe the upper few inches of loose soil, or dragged behind the searcher on a small, light sled. Meteorite hunters have also used more powerful portable electromagnets to collect large amounts of meteoritic material (both solid iron and iron-shale) not only from the surface but also from shallow depths. Even the best of these simple magnetic devices, however, are useless in the detection of really deeply buried meteoritic material.

Meteorites do not merely fall upon the earth (as most astronomical textbooks still insist), but usually penetrate into it—often quite deeply. In fact, one of our mathematical investigations showed that perhaps 100,000 times as much meteoritic nickel-iron is concentrated below maximum plow-depth (approximately one foot) as lies above that depth. Clearly, some form of instrument capable of detecting deeply buried meteorites needed to be devised if this wealth of buried material was not to be lost to science. This need was answered by the development of special _meteorite detectors_.

Although meteorite detectors working on several different principles have been constructed, we shall limit attention here to the simplest and most field-worthy design. The essential principle on which it operates is one familiar to any Boy or Girl Scout who has used a magnetic compass. The first lesson Scoutmasters teach is not to read compass directions from such an instrument when it is held near a mass of iron of considerable size, such as an automobile. Such a large iron mass alters or distorts the local magnetic field of the earth on which the direction-finding ability of the ordinary compass depends. It is this very characteristic, so bothersome to the user of a compass, that is the principle on which meteorite detectors work. For if an electrically driven meteorite detector capable of generating its own magnetic field is carried over a deeply buried iron meteorite, the instrument’s magnetic field will be distorted by the presence of the metal mass, just as the local magnetic field of the earth was distorted by the metal of the automobile.

The operator of such a meteorite detector wears earphones and watches a signal needle in plain sight on the top panel of the detector. Since the phone and signal-needle circuits of the meteorite detector are _in balance_ only when the magnetic field generated by the detector is undistorted, the disturbing presence of a deeply buried meteorite is at once revealed by a shrill note sounding in the earphones and simultaneous motion of the signal needle. If, as in all buried treasure stories, we use “X” to stand for the spot where the signals from the detector are strongest, then the meteorite-hunter has only to dig deep enough at “X” to recover the celestial treasure-trove he is after.

8. THE NATURE OF METEORS

In answer to an exam question, a freshman astronomy student wrote:

A _meteor_ is the flash of light
Made by a falling _meteorite_
As it rushes through the air in flight—
I hope to gosh this answer’s right!

Doggerel or not, the student’s definition correctly stated the true distinction between the two terms, and the teacher marked his off-beat answer correct.

Defined in more scientific terms, a meteor is the streak of light (usually of brief duration) that accompanies the flight of a particle of matter from outer space through our atmosphere. This particle may be as small as a tiny dust grain or as large as one of the minor planets which are called asteroids. Fortunately for the inhabitants of the earth, most of the meteor-forming masses encountered by our globe are of the “small-fry” variety!

As the rapidly moving particle plunges earthward through denser and denser layers of atmosphere, the air molecules offer ever-increasing resistance to its passage. This resistance heats up the meteorite body until it glows. Technically speaking, it becomes incandescent. _The meteor is this incandescence._ We see it as a darting point. Or as a ball of white, orange, bluish, or reddish light. But the _material object_ that produced this light is the _meteorite_. The distinction between these two terms—meteor and meteorite—we must emphasize again and again because people continue to use them incorrectly, as, for instance, when they keep saying “meteor crater” instead of “meteorite crater.”

The majority of the meteors we observe represent the heat-induced “evaporation” of exceedingly small fragments of cosmic matter. The smallest meteor-forming bodies reach the surface of the earth only as the finest of dust particles or as microscopic droplets of solidified meteorite melt.

These residues descend slowly through the atmosphere and may be carried for great distances. Afterwards, they may be found scattered so widely and uniformly on the ground that their presence in any given locality cannot be accounted for by the fall of any specific meteorite. This is a fact that, for example, one school of modern Russian meteoriticists overlooked when they were dealing with tiny granules of meteoritic dust that had been recently found at Podkamennaya Tunguska. These scientists tried to identify the tiny granules with the meteorite that had fallen there, June 30, 1908. But the members of the latest (1958) Russian expedition to that region about the impact point of 1908 clearly recognize the widespread character of meteoritic dust. So they reject the theory that such dust found in the Podkamennaya Tunguska area is specifically connected with the meteorite that fell there a half century ago.

If sizable chunks of meteoritic material enter the atmosphere, they may produce exceptionally large and brilliant meteors. A spectacular meteor is generally known as a “fireball” if it is as bright as Venus or Jupiter. It receives the French term _bolide_ if, in addition to showing great brilliance, its flight is accompanied by detonations like the alarming sounds heard at the time of the Ussuri and Norton meteorite falls.

The term “shooting star,” which is often applied to meteors, in newspapers and magazine articles, is a misnomer. A meteor is _not_ a distant sun (that is, a star) in rapid motion, for the whole path of the meteor lies close at hand within a restricted zone of the earth’s atmosphere.

The word “meteor” comes from the Greek word _meteōra_, which once applied to any natural occurrence _in the atmosphere_—for example, rainbows, halos, auroras, and so forth. Nowadays, the word “meteor” is used in a much more specialized sense than it was by the ancient Greeks. We have a specialized word, _meteoritics_, for the study of meteors and meteorites. No one should confuse meteoritics with _meteorology_, which is the science of things _other_ than meteors and meteorites, in the atmosphere—for example, clouds, storms, air currents.

The region in which meteoric phenomena take place was long the subject of controversy. Some persons felt that meteors were nearby, like lightning. Others said that they moved at the distances of the remote fixed stars. This controversy on the whereabouts of meteors became heated, although it could have been settled quickly by a simple experiment you can try out for yourself.

Hold a pencil against the tip of your nose and look at it first with your right eye closed and then with your left eye closed. Repeat this experiment with the pencil held at arm’s length. In the first case, the pencil will seem to shift position very greatly; in the second, although the same base line (the distance between your eyes) is used, the pencil will seem to shift position only slightly.

Such an apparent shift in position is called a _parallactic displacement_, or, simply, _parallax_. The notion of parallax is of the greatest importance in most branches of astronomy, and it leads (with proper instruments and a little mathematics) to exact determinations of the distances of remote objects.

For our purpose, we need not go into all the interesting but complicated details. Our experiment with the pencil shows that if a meteor was close by, like a blinding bolt of lightning, then, as seen by a pair of observers separated by only a few blocks, the meteor would show a large parallax. But if this meteor was as far away as the stars, it would show no parallax at all, no matter how widely the pair of observers were separated on the earth.

There were many clever scientists among the Greeks, and it is quite possible that a pair of them actually tried out this simple parallax experiment on the meteors and so were able to prove that these beautiful light effects occurred in the high but not too distant layers of the atmosphere. The earliest calculations of meteor heights that are so far known, however, were made in Bologna, Italy, in 1719 and 1745—long after the heyday of Greek science.

The meteor heights found by the Italians were quite low in the atmosphere, probably for two reasons. First, the visual (unaided-eye) observations they had to use were made by eyewitnesses stationed so close together that accurate fixes were impossible. Secondly, these visual observations must have related only to the very brightest and therefore lowest portions of the luminous paths of the meteors through the atmosphere.

In 1798, two German students operating from carefully chosen and widely separated stations began the systematic observation of meteors for parallax. They found that the height of appearance of most meteors lay between 48 and 60 miles above the earth’s surface. It is now known that most meteors, as observed with the naked eye, appear at about 70 miles and disappear at about 50 miles above the surface of the earth. These figures, obtained from visual work, still stand in spite of the development of such modern techniques as photographic and radar recording of meteor paths.

Rarely, meteors may appear at heights of 150 or more miles and fireballs may penetrate to within a few miles of the earth. The average meteors, however, appear and disappear within a well-defined, high-altitude zone in the atmosphere. Fortunately, this atmospheric zone serves us as an effective shield against the constant bombardment of the smaller and much more numerous particles from outer space.

In earlier times, scientists thought that the particles becoming visible as meteors must be tiny dense masses of iron or stone like the material composing the recovered meteorites. Most modern investigators, however, believe that the typical meteor-forming particles may be small loosely bound-together “dust-balls”; that is, fluffy clusters of matter held together by frozen cosmic vapors, generally referred to simply as “ices.” In any event, these masses are usually very small, ranging perhaps from the size of a pinhead to that of a marble.

Because we cannot collect the tiny masses that are seen only as meteors, it is impossible to determine their composition by ordinary laboratory methods. The best we can do is to observe and record carefully the light these masses give off when they become incandescent in their plunge through the atmosphere.

We can examine this meteor light by using the spectroscope and spectrograph. Through these specially designed instruments we can make the meteor light reveal the chemical elements present in the incandescent masses. Each such element sends out light rays as characteristic of its nature as fingerprints are of the individual who made them. Photographs taken of these characteristic light rays are called _spectrograms_, and what might be termed the “fingerprints of light” recorded on these spectrograms are known as _spectra_—which is the plural of the word _spectrum_. If the source of light is a meteor, the photograph shows a meteor spectrum.

From a study of a considerable number of good quality meteor spectra, scientists have found that the principal elements in the masses responsible for meteors are iron, calcium, manganese, magnesium, chromium, silicon, nickel, aluminum, and sodium.

As we have already noted, the resistance encountered by meteor-forming particles as they dash through our atmosphere is so great that they become incandescent and vaporize. These small bodies must therefore be in very rapid motion.

Before we attempt to find out the nature of the paths in space followed by meteorites, we must take into account the fact that these bodies are observed from a station—the earth—which is itself in rapid motion. You may have noticed that on a still day, when rain drops fall vertically downward, the streaks they leave on the windows of a swiftly moving car are not vertical but almost horizontal. Obviously, it would be wrong to say the rain drops are falling from left to right or from right to left when they are actually falling almost straight down, and it is only the forward motion of the car that makes them leave horizontal streaks.

Similarly, neither the apparent speed nor the apparent direction of motion of a meteorite with respect to the moving earth is significant. The important factor is the meteorite’s velocity _with respect to the sun_ at the time the meteorite is picked up by the earth.

This factor enables us to determine in which of two possible kinds of path the meteorite was moving _before_ it was “fielded,” as we might say in baseball, by the earth. This factor tells us whether the meteorite was moving about the sun in a relatively short, closed, oval-shaped path or, instead, was following an indefinitely long, open path which began in the depths of space and would have returned there if the collision with the earth had not prevented.

Either type of path is technically called an _orbit_. The closed orbits are what the mathematicians term _ellipses_; the open orbits, _hyperbolas_.

To scientists, the nature of the orbits followed by meteorites is most important, especially in efforts to determine the mode and place of origin of these bodies. To rocket engineers and astronauts, it also matters a good deal whether the meteorites encountered on flights through space are traveling sedately along closed orbits about the sun or are zipping swiftly along open orbits.

The greater the speed of these cosmic “hot-rods,” the more dangerous they are to space travelers. For example, a mere grain of nickel-iron moving at 40 miles per second is quite as lethal as a .50-caliber machine-gun slug, which, relatively speaking, is traveling at only a snail’s pace.

As our earth moves along its orbit about the sun, meteoritic bodies can run into it from any direction. The direction from which they do approach strongly influences the speed of these bodies as they plunge through the earth’s atmosphere. A meteorite moving slowly about the sun in the same direction as the earth and chancing to catch up with our globe more or less from behind will have an observed speed of only a few miles a second. For example, the speed calculated from Harvard meteor-photographs of one such not-too-spectacular “rear-end” collision amounted to no more than 7.3 miles per second, just about the speed a rocket must acquire to escape from the apron strings of Mother Earth.

In contrast to such a “rear-end” collision, the speed observed would be far greater if the meteorite happened to collide exactly “head-on” with the earth. For, in this case, the orbital speed of our planet would be _added_ to that of the meteorite about the sun. As an example, suppose that at the earth’s average distance from the center of our Solar System, the speed of a meteorite with respect to the sun were 32.23 miles per second. (This speed was actually found for the mass that produced one of the first meteors photographed simultaneously by the Harvard stations at Cambridge and Oak Ridge, Massachusetts.) Then if such a meteorite ran “head-on” into the earth, the speed observed for it in the atmosphere would be over 51 miles per second. And mathematics would show that the orbit of this meteorite with respect to the sun was a wide open hyperbola.

If the orbit of the earth and the orbit of a swarm of particles of cosmic matter intersect, and if the earth and the swarm pass through this intersection in space at nearly the same moment, multitudes of meteors appear. We then say that a _meteor shower_ takes place. The position of the point at which the particle-swarm crosses the earth’s orbit about the sun fixes the date of the meteor shower.

Because the particles that make a meteor shower are moving through space along parallel paths as they come into the earth’s atmosphere, the meteors all seem to shoot out from a single small area in the sky. You may have seen something like this in the case of the sunrise or sunset effect known as “the sun drawing water.” In this more familiar phenomenon, the sun’s disk is the area from which shafts of sunlight radiate out in a beautiful, if somewhat irregular, fan-like pattern. The area from which the meteors of a given shower seem to come is the _radiant_ of that shower.

Meteor showers are named for the constellation in which their radiant lies. The suffix “-id” (Greek for “daughters of”), or some modification of this suffix, is added to the name of the constellation from which the meteors seem to radiate. The Orionid radiant, for example, is in Orion, the Hunter; the Leonid radiant is in Leo, the Lion; and the Lyrid radiant is in Lyra, the Harp. Exceptions to this rule do occur, however. Astronomers may refer to a shower sometimes appearing on the night of October 9 as the “Giacobinid” shower in honor of the comet Giacobini-Zinner, which is associated with this particle-swarm.

In the course of each year, the earth passes through a number of particle-swarms of varying densities. Some of the resulting meteor showers, like the Leonids and Giacobinids, are very feeble in most years, but sometimes produce spectacular displays.

The more important recognized meteor showers are:

NAME OF SHOWER DATE OF MAXIMUM
Quadrantids January 1-3
Lyrids April 21
Eta-Aquarids May 4-6
Perseids August 10-14
Giacobinids (Nu-Draconids) October 9
Orionids October 20-23
Leonids November 16-17
Geminids December 12-13

Certain daytime streams are also known to be active during June and July. These daytime showers are, of course, invisible in the glare of sunlight, but they can be picked up by radar devices like those used in World War II to spot enemy airplanes.

Some meteor showers have been splendid enough to make a place for themselves in the historical record. Examples are the Leonid returns of 1833 and 1866, and the Giacobinid showers of 1933 and 1946. During these displays, meteors fell in a veritable fiery snowstorm, several hundred meteors sometimes appearing within a minute.