Astronomy

The term meteor comes from the Greek meteoron, meaning phenomenon in the sky. It is used to describe the streak of light produced as matter in the solar system falls into Earth’s atmosphere creating temporary incandescence resulting from atmospheric friction. This typically occurs at heights of 80 to 110 kilometers above Earth’s surface. The term is also used loosely with the word meteroid referring to the particle itself without relation to the phenomena it produces when entering the Earth’s atmosphere. A meteoroid is matter revolving around the sun or any object in interplanetary space that is too small to be called an asteroid or a comet. Even smaller particles are called micrometeoroids or cosmic dust grains, which includes any interstellar material that should happen to enter our solar system. A meteorite is a meteoroid that reaches the surface of the Earth without being completely vaporized.

One of the primary goals of studying meteorites is to determine the history and origin of their parent bodies. Several achondrites sampled from Antarctica since 1981 have conclusively been shown to have originated from the moon based on compositional matches of lunar rocks obtained by the Apollo missions of 1969-1972. Sources of other specific metorites remain unproven, although another set of eight achondrites are suspected to have come from Mars. These meteorites contain atmospheric gases trapped in shock melted minerals which match the composition of the Martian atmosphere as measured by the Viking landers in 1976. All other groups are presumed to have originated on asteroids or comets; the majority of meteorites are believed to be fragments of asteroids.

Meteorite Types & Percentage that Falls to the Earth

• Stony meteorites
  • Chondrites (85.7%)
    • Carbonaceous
    • Enstatite
  • Achondrites (7.1%)
    • HED group
    • SNC group
    • Aubrites
    • Ureilites
• Stony iron meteorites (1.5%)
  • Pallasites
  • Mesosiderites
• Iron meteorites (5.7%)

Meteorites have proven difficult to classify, but the three broadest groupings are stony, stony iron, and iron. The most common meteorites are chondrites, which are stony meteorites. Radiometric dating of chondrites has placed them at the age of 4.55 billion years, which is the approximate age of the solar system. They are considered pristine samples of early solar system matter, although in many cases their properties have been modified by thermal metamorphism or icy alteration. Some meteoriticists have suggested that the different properties found in various chondrites suggest the location in which they were formed. Enstatite chondrites contain the most refractory elements and are believed to have formed in the inner solar system. Ordinary chondrites, being the most common type containing both volatile and oxidized elements, are thought to have formed in the inner asteroid belt. Carbonaceous chondrites, which have the highest proportions of volatile elements and are the most oxidized, are thought to have originated in even greater solar distances. Each of these classes can be further subdivided into smaller groups with distinct properties.

Other meteorite types which have been geologically processed are achondrites, irons and pallasites. Achondrites are also stony meteorites, but they are considered differentiated or reprocessed matter. They are formed by melting and recrystallization on or within meteorite parent bodies; as a result, achondrites have distinct textures and mineralogies indicative of igneous processes. Pallasites are stony iron meteorites composed of olivine enclosed in metal. Iron meteorites are classified into thirteen major groups and consist primarily of iron-nickel alloys with minor amounts of carbon, sulfur, and phosphorus. These meteorites formed when molten metal segregated from less dense silicate material and cooled, showing another type of melting behavior within meteorite parent bodies. Thus, meteorites contain evidence of changes that occurred on the parent bodies from which they were removed or broken off, presumably by impacts, to be placed in the first of many revolutions.

The motion of meteoroids can be severely perturbed by the gravitational fields of major planets. Jupiter’s gravitational influence is capable of reshaping an asteroid’s orbit from the main belt so that it dives into the inner solar system and crosses the orbit of Earth. This is apparently the case of the Apollo and Vesta asteroid fragments.

Particles found in highly correlated orbits are called a stream components and those found in random orbits are called sporadic components. It is thought that most meteor streams are formed by the decay of a comet nucleus and consequently are spread around the original orbit of the comet. When Earth’s orbit intersects a meteor stream, the meteor rate is increased and a meteor shower results. A meteor shower typically will be active for several days. A particularly intense meteor shower is called a meteor storm. Sporadic meteors are believed to have had a gradual loss of orbital coherence with a meteor shower due to collisions and radiative effects, further enhanced by gravitational influences. There is still some debate concerning sporadic meteors and their relationship with showers.

Chondrite Meteorite

This meteorite was collected from the Allan Hills in Antarctica. Meteorites are bits of rock that are captured by a planet’s gravity and pulled to the surface. This meteorite is of a type named chondrite and is thought to have formed at the same time as the planets in the solar nebula, about 4.55 billion years ago.

Achondrite Meteorite

Discovered at Reckling Peak, Antarctica, this type of meteorite is known as an achondrite. It has a basaltic composition and was probably formed when an asteroid melted about 4.5 billion years ago. The asteroid broke up some time later and this small piece of the asteroid was captured by Earth’s gravity and fell to the ground.

Iron Meteorite

This iron meteorite was found at Derrick Peak, Antarctica. This type of meteorite gets its name because it is mostly made of the elements iron and nickel. This sample is probably a small piece from the core of a large asteroid that broke apart.

Martian Meteorite

Even though this meteorite was collected in Elephant Moraine, Antarctica in 1979, some scientists believe that it came from the planet Mars. The minerals found in this rock are similar to those that scientists expect to find in rocks on Mars. This meteorite also contains vesicles, or shiny pockets, which contain air very much like the air measured on Mars by the Viking spacecraft. This meteorite is 180 million years old.

A Martian Meteorite

This meteorite, called EETA 79001, was found on the ice in Antarctica, and is quite likely from Mars. For scale, the cube at the lower right is 1 centimeter on a side. The meteorite is partly covered by a black glassy layer, the fusion crust. The fusion crust forms when the meteorite enters the Earth’s atmosphere at high speed. Friction heating melts the outer portion of the meteorite. Inside, the meteorite is gray. It is a basalt, very similar to basalts found on Earth. It formed in a volcanic eruption about 180 million years ago. This meteorite is quite likely from Mars because it contains a small amount of gas that is chemically identical to the Martian atmosphere.

Microscopic View of a Martian Meteorite

Rocks are often made of small mineral grains that can’t be seen clearly without a microscope. To see these small grains, scientists grind and polish rock samples very thin so light can pass through them. This microscopic view, 2.3 millimeters across, is in false color, produced by holding polarizing filters above and below the microscopic slide. These filters cause different minerals to have distinctive colors, allowing easy identification of the minerals. Most of this meteorite (in yellow, green, pink, and black) is the mineral olivine, which is common in some basaltic rocks. The striped grain near the center is the mineral pyroxene.

Vesta Meteorite

This meteorite is assumed to be a sample of the crust of the asteroid Vesta, which is only the third solar system object beyond Earth where scientists have a laboratory sample (the other extraterrestrial samples are from Mars and the Moon). The meteorite is unique because it is made almost entirely of the mineral pyroxene, common in lava flows. The meteorite’s mineral grain structure also indicates it was once molten, and its oxygen isotopes are unlike oxygen isotopes found for all other rocks of the Earth and Moon. The meteorite’s chemical identity points to the asteroid Vesta because it has the same unique spectral signature of the mineral pyroxene. Most of the identified meteorites from Vesta are in the care of the Western Australian Museum. This 636-gram specimen comes from the New England Meteoritical Services. It is a complete specimen measuring 9.6 by 8.1 by 8.7 centimeters, showing the fusion crust, evidence of the last stage in its journey to Earth.

Having accepted atomism, it is necessary to account for the differences between solid, liquid, and gaseous states. Matter in any of these states consists of molecules. Ice, water, and steam represent three states of the same compound of hydrogen and oxygen. Mercury, an element not a compound, can be solid, liquid, or gaseous. Usually a solid passes through a liquid state before becoming gaseous: however, it is possible, at certain temperatures and pressures, for solids to pass directly to the gaseous state or from gas to solid.

It has been seen that the result of heating a body (increase in temperature) is to increase the energy of motion (kinetic energy) of the molecules of which it consists. In the solid state the molecules are thought to be bound together by certain forces so that we have a condition of stability and, to a degree, orderly and permanent arrangement. For the present we need not be concerned with the details of shape and arrangement of the molecules. Perhaps it is sufficient to imagine a box full of egg-shaped rubber balls bound together by thin rubber bands. If the balls are hollow and contain a mechanism which will make them vibrate, we will have a vibrating mass, the individuals of which are limited in their movements. If the effect of the internal mechanisms could be controlled so that the agitation could be varied, we would be able to demonstrate in a crude manner the ” solid” at various temperatures.

When the temperature was increased to the proper value, the elastic bands would break and the individuals would be freed. They would then begin to bounce and collide haphazardly and would try to escape from the room. This would be a crude picture of a gas.

A crystal could be pictured the same as any other solid, but the molecules would be arranged in a more orderly manner.

If a room contains many elastic balls bouncing here and there, we have a picture of a gas. Suppose that a layer or two settles to the floor, but still is in an agitated state. This may be considered a crude model of a liquid above which is its vapor.

By rubbing two solids together their temperature is increased by an amount equal to the work done in overcoming friction. It may be considered that the molecules in the surface layers have been excited into more violent movement resulting in greater average kinetic energy, hence, in higher temperature.

Absolute zero is that lowest possible temperature at which the molecules of matter cease to vibrate. This logically follows from the kinetic theory of heat and of matter. Absolute zero is at about 4590 F. below the ordinary Fahrenheit zero or 4910 F. below the freezing point of water. On the Centigrade scale it is about 2730 C. below the Centigrade zero which is at the freezing point of water.

It is well known that a liquid is cooled by evaporation. If we consider that a liquid consists of molecules moving haphazardly (within certain limits) due to collisions with each other, some of these molecules will have sufficient speed to escape the attractions of their neighbors. These, then, find themselves in the space above the liquid and are now a part of the vapor above the liquid. Inasmuch as the only molecules which escape are those having a great enough velocity in a direction away from the surface of the liquid, it is obvious that the liquid is losing only those molecules which at the time of escape have much more than average kinetic energy. Such losses result in a lower average velocity of the molecules left in the liquid and therefore the temperature of the liquid decreases.

Inasmuch as the molecules of matter do not cease to vibrate or to move about until absolute zero is reached, it is obvious that there is much kinetic energy in bodies at ordinary temperatures. A piece of ice is cold to us, but it is relatively hot compared with liquid air and even more so compared with absolute zero. Here we must eliminate our sense of temperature and look at Nature without this prejudice. There is enough total kinetic molecular energy in a piece of ice the size of a baseball to raise a ton weight more than 30 feet vertically. If we could find a means of extracting the total kinetic energy of the molecules of a piece of ice of this size each second, we would have the equivalent of a motor of about two horse-power. It should be noted that the foregoing involves only molecular energy and not so-called chemical and atomic energy.

Other Applications of Atomism

The great success of the atomistic principle as it is involved in the kinetic theory of matter is one of the wonders of the modern scientific age. It is to be expected that it has found other applications equally fascinating and promising. It is now being pressed further into the service of explaining the structure of matter. Molecules are not only divided into atoms, but the latter are now known to consist of still smaller particles. The reality of the electron is thoroughly established. It takes 1800 electrons to equal in mass that of an atom of hydrogen which has the smallest mass among the atoms of elements.

When Maxwell (1873) propounded the electromagnetic theory of light (radiation), his achievement was epochal. The exact manner in which the radiant energy traversed space was not known, and the next epochal event was the founding by Planck (1900) of the quantum theory. Here we have the atomistic principle applied to energy instead of being confined to the material of the universe as it had been. In other words, in the quantum theory we have the atomistic idea applied to physical processes. We now have the atom of matter, the atom (electron) of electricity, and the atom (quantum) of action (a product of energy and time). Planck assumed the emission of radiation (from the sun, a lamp filament, etc.) to occur discontinuously. He conceived elements of energy of equal magnitude analogous to the equality of electrons, or atoms of a given element. Radiation or radiant energy is emitted of various wavelengths or frequencies which must be taken into account in laws of radiation. By inventing the quantum of action Planck was able to derive a law of radiation which explained the experimental data hitherto not understood. The elementary quantum of action is equal to the elementary quantum of energy multiplied by the frequency of the radiation. Thus again, we find science in a state which required a creative mathematical physicist to iron out inconsistencies, to put the finishing touches on existing theories, and to explain much of the accumulated data.

Now the physicist uses quanta as commonly as he does electrons and atoms and molecules. Bodies are built of molecules, the molecules of atoms, and the atoms of electrons (and protons) . Here we see the atomistic principle applied to ” material” (matter) and then to electricity (What shall we call it?). Finally, a physical process - the radiation emitted by the electrons - is divided into quanta. With such pictures of the universe being constructed we may cease to be surprised at anything, but our interest and admiration will grow. Will we ever get to the final foundation? Will mind be finally explained by the physicist?

These are mere glimpses of the electron theory and the quantum theory introduced to complete this portion of the picture for the present. They are so important, so modern, and 50 far-reaching that they are treated later in more detail.

It is interesting to view the particles of gas more intimately.

The velocity of a molecule of gas depends upon its mass. At the temperature of melting ice, hydrogen molecules have an average velocity of about one mile per second. Oxygen molecules being about sixteen times heavier travel about one fourth as fast as hydrogen molecules. These velocities are of the order of magnitude of projectiles fired from guns. It is fascinating to think of the nitrogen and oxygen molecules of the air about us moving between collisions with the velocities of bullets. They are striking our faces with these velocities and it is obvious that we should be thankful for their very small mechanical energy. We cannot conceive the smallness of the mass of a hydrogen molecule. Its mass is related to that of a baseball about as the mass of the baseball is to that of the Earth. There are about 102.5 molecules of hydrogen per ounce of the gas, or 10 million billion billion molecules or 10 trillion trillion molecules per ounce. The reader may take his choice of these numbers, but it is likely that the baseball comparison of relative mass gives a better idea of the size than the foregoing numbers. The diameter of the hydrogen molecule is less than ten billionths of an inch (8.5 X 10-9 inch). Particles must be a thousand times larger to be visible under the most powerful microscope.

Perhaps some idea of the number of molecules in an ounce of hydrogen gas might be obtained if we set out to count them.

There are about two billion persons on Earth. Suppose each was able to count 100 molecules per minute continuously. It would take the entire population of the Earth one hundred million years to count the molecules in an ounce of hydrogen gas. The mass of the Earth is again inconceivably greater than the mass of hydrogen weighing an ounce at the Earth’s surface, so it is seen that the number of molecules in the Earth alone is quite beyond comprehension. Similarly the greatest known distances in the stellar universe are inconceivably large. The human being is puny indeed and his mind can never comprehend the picture in its entirety. Nevertheless, we may enjoy knowing that there will always be awesome magnitudes to contemplate when we desire to exercise our imagination. There would be a maximum of about 7 billion molecules in a single row of them five feet long and it would take a person a lifetime to count the number in this short row of molecules in “single file.”

The Statistical Method

In dealing with molecules and other minute particles of matter which are shooting about as in the case of a gas confined in a vessel, we cannot arrive at any definite conclusion without studying averages. A single molecule, if we take averages, collides billions of times per second. If we direct our mind’s eye upon anyone molecule of a gas, we will find that its path is hap-hazard, unpredictable, and quite accidental. The same is true of the course of life of any human being. However, the insurance companies by observing a large number of persons can make sufficiently accurate predictions upon which to base a sound business. Anyone of us may die the next moment, or fall out of a window tomorrow, or collide with a street-car the next day. When an individual will marry, how many children he will have, or how much money he will acquire, only the future can tell us. No one can predict what will happen in a particular case, but from adequate records of a sufficient number of cases a safe prediction can be made based upon the” law of averages.” Many applications daily are now made of the results of statistics and science has successfully utilized the statistical method in various ways.

Maxwell (1841-1879) was the next great mathematical physicist after Newton to greatly change the course of scientific thought. Although he has greater scientific achievements to his credit, he placed the kinetic theory of gases on a firm foundation from which it has not been shaken, by developing the statistical method. He applied natural laws to the individual molecules, but without attempting to follow an individual he gave his attention to totality. It has been seen that the number of molecules in even a small quantity of matter is very great; therefore, we can have faith in the law of averages.

It is certain that the movements of molecules of a gas depend upon less complicated factors than the lives and activities of human beings. All molecules of the same element or gas have equal masses, with slight exceptions of no consequence at this time. The kinetic energy of anyone is determined by its mass and velocity. The mean velocity of the molecule, based upon the study of the combined effect of the billions of molecules, is a very definite and constant value for any given set of conditions. In fact, about all we must convince ourselves of in order to have faith in the statistical method as applied to gases, is that the rate of collision of molecules is constant for a given pressure, volume, temperature and gas.

Perhaps it will aid the reader to have faith if we revert momentarily to the number of molecules. A minute sphere two thousandths of an inch in diameter is about as small an object as we can see with the unaided eye at a distance of one foot. If this sphere were filled with gas at atmospheric pressure and of ordinary temperature, it would contain about 2000 billion molecules. Expressed in another way this number is equivalent to two million-million. Counting at the rate of 100 per minute for the usual working hours throughout a year, it takes a person a lifetime to count a billion. At this rate it would take 2000 persons their entire lifetime to count the molecules in that minute sphere two thousandths of an inch in diameter. Insurance can be safely based on the statistics of a number of persons, relatively few compared with the number of molecules in a sphere invisible to the unaided eye. Considering this fact along with the more complex vagaries of human beings as compared with those of molecules, it is seen that we can have utmost faith in the constancy of the results of the statisical method as applied to molecules of matter. Maxwell established these facts beyond question.

Brownian Movements

If we suspend in air an object easily visible to the unaided eye, it will be subjected to collisions from all directions, of molecules of the gases in the atmosphere. But we do not see it move here and there because it is being bumped from all directions. The number of molecules colliding with it per second is inconceivably large. Even in the smallest part of a second necessary for our consciousness to note a movement of this small suspended object, it would receive billions of impacts. The force upon it would be equal in all directions owing to the application of the law of averages so that even if it had no mass, it would not be moved appreciably.However, if we reduce the size of this suspended object, we should be able to arrive at a point where there is not a sufficient number of collisions from all directions for the effect to be equalized on all sides. In other words, the particle would be subjected to different forces from various sides and we would expect it to be bumped here and there in a haphazard fashion. Brown (1773-1858), a botanist, while examining under a microscope some liquids containing particles of pollen about one thousandth of an inch in diameter, noticed that these particles moved irregularly. He also noticed that the movements were more conspicuous for the smaller particles. Brown did not explain this, but, scientist that he was, he recorded his keen observations.With the establishment of any new principles and generalizations which are shown to be sound, many of the observed facts of past records are explained. Brown’s observations were to await the kinetic theory of matter before true light could be shed upon them. Hence, about fifty years later the Brownian movements were shown to be due to the impacts of molecules of the liquid in which the pollen particles were suspended. The same kind of movements have since been demonstrated in gases. It has been shown that fine particles of matter, such as gamboge suspended in water, obey the same laws that have been applied successfully to molecules. Some of this work has provided experimental foundation for the theory that the average energy of motion of the particles or molecules of a mass of matter depends only upon the temperature of the matter and not upon the mass of the particles. It was also shown that these particles, although very much larger than molecules, had an average energy of rotation equal to their average energy of translation. This also added support to the prevalent theory.

It is seen that the study of Brownian movements contributed much toward the establishment of the kinetic theory of matter.

The atomistic principle rendered a very great service in the development of a picture of gases which could account for such properties as pressure. Newton’s mechanics, which contributed so much toward our knowledge of the stellar universe, finds a beautiful application to the molecules of a gas. Although the conception of the idea of the kinetic theory of gases can be traced further back, Clausius ( 1857) really founded it after Joule (185 I) had attempted to calculate the velocity of a hydrogen molecule. The calculations were inexact, but they mark the beginning of an actual atomic view of matter as distinguished from the mere symbolic view of the chemist up to that time.

The molecules of a solid are considered to be bound to certain positions which result in equilibrium, but this is not the case in gases. The molecules of a gas are continually in motion, excepting at absolute zero, about 491 degrees Fahrenheit below the melting-point of ice. At first they were likened to elastic spheres shooting in all directions and colliding with each other. At ordinary temperatures and pressures a gas-molecule will suffer several billion collisions each second. Although the modern ideas of the atom are not fully developed in relation to the kinetic theory of gases, it is likely that the molecules do not actually collide in the ordinary sense. The modern conception is that atoms are tiny planetary systems of electrons revolving around a positive nucleus. Doubtless they are surrounded by electric forces so that instead of a collision we have a repulsion of the electric forces. At any rate the true picture is of little consequence here because it will not alter the actual facts.

The pressure on the sides of a vessel containing a gas is due to the billions of collisions of the molecules with the sides. The force of an impact is determined by the mass and the velocity. The pressure is the result of the number of impacts per second. If the density of the gas is doubled there will be twice as many impacts in a second on a given area of the vessel and, therefore, the pressure will be doubled. This relation of density and number of molecules was suggested by Boyle (1627-1691) which gave rise to Boyle’s law. This law states that, for a given temperature, the product of the pressure and the volume is constant.

The temperature of a gas is determined by the mean energy of motion of a molecule. Here again Newton’s mechanics enter, for the energy of motion of a molecule is proportional to its mass and to the square of its velocity. As the temperature decreases, the energy of motion (kinetic energy) of a molecule decreases until at absolute zero there is no motion. Hence, at absolute zero the pressure of any gas is zero. It may be of interest to know that absolute zero has not quite been reached in the laboratory, but it has been approached to within less than a degree Centigrade.

The atomistic idea has not been limited to the structure of matter by any means. It is associated with several properties or characteristics of matter such as heat, gas-pressure, and light or radiant energy. The early idea of heat was that it was a fluid. Count Rumford (1753-1814) a little more than a century ago was one of the first to relegate this idea to the discard by experiments which suggested that heat was a mode of molecular motion. It is true that Roger Bacon (12141294) suggested heat was a matter of agitated particles such as molecules, but as in other phases of science, experimental data were lacking. Mayer and Joule (1842) discovered that mechanical work was converted into heat and that the amount of heat was always exactly proportional to the amount of work and vice versa.

It had long been recognized as a direct consequence of Newton’s laws of motion, that energy could not be destroyed. This is the well established law of conservation of energy. For example, if a moving body collided with another body, the resultant mechanical energy remained equal to the total before the collision. The total mechanical energy required to produce a certain amount of heat (agitation of the molecules of the body in which the heat was generated) would remain unaltered. The molecules of the body now possessed so much more mechanical energy; in other words, they were sufficiently more agitated so that their excess mechanical energy was just equal to the mechanical energy required to produce the amount of heat that the body received.

Thus we see not only the atomistic idea of matter used to account for a change in temperature (due to the production of a certain quantity of heat), but also Newton’s laws of motion applied to the molecules of the body. It is a beautiful picture of unification. For example, suppose a large iron ball is dropped from a height and it strikes a thick iron plate of great mass. The mechanical energy of the falling ball at the moment before striking the plate is proportional to its mass and the square of its velocity. Actually the ball will bounce a few times, but let us assume it always hits in the same place and comes to rest there. The energy of the ball is now distributed among myriads of molecules of iron both in the plate and in the ball. Owing to the minuteness of the agitated molecules we cannot see their increased movements, but we can feel the result of the increase. The two bodies are of a higher temperature at first only near the points of contact, but the heating effect rapidly spreads and equalizes. This is what we term conduction of heat and is really a communication of the increased agitation to other molecules. It should be noted that the molecules of a body are always in a state of agitation (excepting at absolute zero), the degree of agitation being indicated by the temperature.

Perhaps to a primitive mind the earth consists of stones, grains of sand, dust particles, drops of water, and similar things. In other words, it is made up of parts. One cannot contemplate Nature for long without noting that disintegration and transformation are continually going on. Ice melts to water; the water vaporizes; the vapor condenses again to water; it freezes to ice. Clouds dissipate themselves in rain or snow. Rock disintegrates into sand; the sand into dust; the dust is carried away by wind and water. Thus, visible things become invisible and the invisible may become visible.

It is not surprising that Anaxagoras (500-428 B.C.) propounded the principle that the material of Nature was compounded of and could be resolved into elementary seeds of matter. This idea found advocates throughout the ages, although it was little more than a speculation in early centuries. Leucippus believed that the universe consisted of limitless empty space and of matter, the latter consisting of numberless, indivisible atoms. He also thought that atoms were always in motion. As usual, there were many fantastic ideas interwoven in these speculations.

Democritus (460-370 BC), a pupil of Leucippus, developed the theories of his teacher to such an extent that generally his name is the only one associated with these early speculations of empty space and atoms as elements of the cosmos. He also developed the idea that all the material of the universe was produced by the motions of these atoms. He was an extreme sceptic as indicated by the remark attributed to him, “We know nothing; not even if there is anything to know.”

Although many of his speculations can be very easily modified to fit the facts of the physical world as we know it today, he contributed little of real note to science excepting an example of the value of a critical attitude. Nevertheless, the idea of atomism had to have a beginning and it matters not if it began in metaphysics and alchemy. It has eventually arrived a definite reality. It aided in the development of chemistry which in turn developed atomism. Spectroscopy did much to place the atomic theory of matter on a firm foundation. Finally radio-activity, that marvelous exhibition of the birth of one element from another, has made us even better acquainted with the atom.

In the development of the atomic theory of matter, the foundational laws of the great stellar world were applied to the tiny worlds far beyond the revealing power of the microscope. The great laws which were developed to explain the motions of the Moon, planets, and other celestial bodies and were so clarified by Newton, soon began to serve to explain the structure and properties of matter and eventually of atoms themselves. Motions and masses were attributed to minute molecules, atoms, and electrons with the result that the energy of motion of these small particles became a very important factor in explaining various physical phenomena. Hence, the introduction of the term, kinetic energy. As will be shown later, modern developments impose limitations upon the applications of Newtonian mechanics, but for the present we need not consider them in detail.

By this time considerable knowledge of the movements of matter was available. Galileo’s work with the pendulum, with falling bodies, and with projectiles had established a number of facts. Kepler’s laws of the movements of the planets were available. In fact, much data of matter and motion had accumulated and the time was ripe for a generalization. Coordination of various laws and phenomena was lacking. This situation is reached every so often in scientific development and opportunity awaits the genius capable of the great work to be done. When opportunity and genius meet a notable epoch is the result. Such a time awaited the coming of Newton (1642-1727) and he did not fail.

Newton’s imagination conceived the idea of an essential deadness of matter; that is, that matter could not of itself change its state of motion or of rest. Something had to do this for matter. This fundamental characteristic of matter he termed mass. It is something which, according to Newton, does not change. Einstein’s modern view, which seems to be well founded, shows that Newton’s theory is correct only under specific conditions. However, it happens that these specific conditions are the ones we are ordinarily concerned with so that Newton’s theory is practicable for our everyday use.

If matter could not move itself or change its state of motion, something had to be “invented” to do this, because it is well known that matter falls, that stones roll down hill that the tides ebb and flow. For this purpose Newton’s imagination created force. It was purely a hypothesis because it is not observed. We only observe its result as a change in motion. His great achievement was a definition of force which explained the movements of failing bodies on the Earth as well as of celestial bodies such as the Moon and planets revolving about the Sun.

If force is responsible for the change of motion of a body, the rate of change which it produces must be a measure of it. After considering the problem from various viewpoints he finally defined the quantity of motion of a body as the product of its mass and its velocity. Therefore, the change in velocity of a body due to a certain force was greater for a body of small mass than for one of a larger mass. This is the first introduction of the idea of mass as a property of matter. It became established that mass could not be destroyed and that it was constant for a given body. If the body was broken into parts, the sum of the masses of the parts equaled the original mass.

If the mass of a body is constant a change in motion must be due solely to a change in velocity which is acceleration in the case of increased velocity. Newton’s hypothesis of force is that it is equal to the mass times its acceleration. The weight of a body is really the force of the Earth’s attraction and may be stated thus; Weight or Force equals Mass times the gravitational constant g. This may give an idea of the difference in the weight of a body at different distances from the center of the Earth. Inasmuch as the Earth is flattened at the poles, a body at the North Pole is somewhat nearer the center of the Earth than one at the equator. Hence, a body is heavier (it weighs more) at the pole than at the equator. In other words, the weight of a body is variable because the gravitational constant is variable, the mass being constant.

Newton’s law of gravitation or of attraction between bodies is as follows;

The force of attraction between two bodies (masses) is proportional to the product of their masses divided by the square of the distance between them.

This law has been invaluable to all branches of physics throughout the atomic and stellar realms. By means of this law and his laws of motion many far-reaching conclusions in physical science have been reached. It is easily understood why the ((weight” of an object varies for different locations in space. For example, an object on the surface of the Earth is approximately 4000 miles from the center of the Earth. Suppose it has such a mass that the mutual attraction is a force of I 60 pounds; that is, the weight of the object, say a man, is 160 pounds. At a distance 4000 miles above the Earth’s surface, the man would be twice as far from the Earth’s center and, therefore, would weigh only 40 pounds. It will be recalled that the force of attraction varies inversely as the square of the distance. If the man were in space at the distance of the Moon (240,000 miles) and the Moon were as far away as possible so its influence was negligible, the man would weigh about two-thirds of an ounce.

Newton’s laws of motion may appear rather obvious to us, nevertheless, they were wonderful conceptions. They are axioms which cannot be directly proved, but they fit data and experiences so well that they have been indirectly proved (with limitations) almost to the satisfaction of us Earth-beings. These laws are as follows:

1. Any body persists in its state of rest or of uniform motion in a straight line, unless acted upon by an external force.
2. Rate of change of motion is proportional to the force applied and is in the direction of this force.
3. To every action there is always opposed an equal reaction.

These laws will be recognized as a part of that often uninteresting course of physics which most of us have had at some time or other. But the interest is largely a matter of viewpoint and lies within the individual. Here it is hoped that these laws will be looked upon in a different light - as a fundamental and vital part of a wonderful structure which to us is the physical world. We have no means for proving these laws any more than we can prove any fundamental. A great structure was satisfactorily built upon them so they were accepted as correct. We cannot prove that a body will continue moving forever along a straight line unless acted upon by other forces, because other forces always exist. The second law shows how a force can be measured because it is really the definition of a force. The third law indicates that if a force is applied to a body an equal force (exerted by the body) must be overcome. For example, the Earth is pulling just as hard on a body that we are holding in our hands as we are.

Let us look at one of the difficulties that confronted Newton in his labors to unify the motion of bodies by means of fundamental laws. The falling of an object to the Earth seems quite unrelated to the revolution of the Moon around the earth or the planets around the Sun. The falling object travels in a straight line; the Moon and the planets travel in closed curves - ellipses. Furthermore, the velocity of a falling object continually increases; the velocities of the Moon and planets are more nearly constant, only varying between reasonably small limits. Add to these differences, the fact that a “heavy” body falls from a given height in the same time as a “light” one (neglecting air resistance).

It has been seen that Newton propounded the law that the attractive force between two bodies was proportional to the product of their masses. That is, a stone was pulled by the Earth and the latter was also pulled by the stone. Suppose one stone had three times the mass of another. It would be pulled three times as hard by the Earth, but it would also have three times the resistance to the Earth’s pulling force. This results in equal accelerations of the two stones when dropped from the same height. As a consequence they fall together about 16 feet the first second, 64 feet the next second, 144 feet the third second, and so on.

In order to explain why the Moon does not fall to the Earth due to the attraction of it, it was necessary to attribute to it a motion of its own. If the Moon and the Earth had no independent motion and no other forces, but their own gravitational forces were acting, they would be drawn toward each other. The Earth would move slightly toward the Moon, but the latter would move most of the way because of its lesser mass. In fact as the Earth proceeds on its elliptical path around the Sun, the Moon in revolving around the Earth pulls the Earth slightly to and fro so that the Earth’s path is slightly wavy. From accurate measurements of these variations it is determined that the mass of the Earth is about eighty-one times that of the Moon. After Kepler established his laws and the elliptical orbits of the planets, the variations from true ellipses of the actual paths of the planets due to the mutual attractions of the planets, were subjected to close scrutiny by Newton. He found that the laws that he had formulated accounted for most of these variations very well. This led him to the universality of the law of gravitation.

It should not be difficult to conceive of the Moon, the planets, and other celestial bodies having an independent motion. If a bullet could be projected from the Earth at a sufficient velocity it would not fall to the Earth. It would go on traveling in a curved path which finally would be the resultant of its independent motion and of the change in motion due to the Earth’s gravitational force. It would then go on describing a closed orbit around the Earth. It loses none of its velocity due to resistance of the medium of space because as far as we know space is a void from a material viewpoint. The Earth’s force of attraction is satisfied by continually changing the direction of the path of the new “bullet” satellite.

If one has not thought of these matters seriously it may be difficult at first to conceive the possibility of the Moon not falling to Earth. Remember the tendency of the Moon is to travel forever in a straight line unless acted on by other forces. The Earth’s force is the only important external one for the Moon, owing to the proximity of the Earth compared with other bodies. Under the action of the Earth’s attraction the Moon does not travel in a straight line, but is pulled all the time from its straight-line tendency. The resultant is a closed curve at each point of which the position of the Moon is the resultant of all the forces acting. We are used to forces dissipating. We do not hope for perpetual motion in our mechanisms, because we cannot get rid of friction. A heavenly body is a mechanism of perpetual motion because, as it travels through the nothingness of space, there is no friction and therefore no loss of its own momentum in that respect. Apparently there are similar mechanisms within the atom.

Limitations of Newton’s Laws

Newton’s laws of motion and gravitation are epochal because they are really the foundation of dynamics. They were amply verified throughout many years and were the basis of physics for two centuries. As already stated they are still acceptable for all practical purposes of the Earth being, but being based upon absolute space, time, and matter they are shown to be only special cases of Einstein’s wonderful conception of the cosmos which is discussed later. Einstein, who can be credited with one of the greatest achievements of human thought, has said, “Newton’s theory is probably the greatest stride ever made in the effort toward the causal nexus of natural phenomena.” These laws explained observed data and predicted phenomena very well for all practical purposes and for most scientific ones. But certain observations in astronomy were not quite satisfied by them. In new physics, some phenomena connected with rapidly moving small particles and with light and radiation was not accounted for by the Newtonian laws. As has been stated, this assumption of absolute time, space and matter satisfied the Earth-being in his everyday affairs and also if his observations did not extend too carefully into the stellar and atomic worlds.

Einstein became dissatisfied with certain inconsistencies that had arisen between theoretical physics and observed data. He began with the premise that time was not absolute; that is, that statements of time depend upon the viewpoint of the observer and that two observers moving with respect to each other would differ in their statement of time. Einstein built up a principle in which space, time and matter are relative, hence, the principle of relativity. This was destined to revolutionize scientific thought. The velocity of light now plays in physics what infinity does in mathematics. Statements of time must satisfy the demand that the velocity of light is invariable in all directions. Mass varies with the velocity of the body, becoming infinite at the velocity of light. When a mass becomes infinite a force acting on it cannot alter its velocity, therefore, the velocity of light is the highest attainable. Mass becomes associated directly with all energy, and energy with all mass. The failure of Newton’s laws is chiefly noticeable when dealing with velocities approaching that of light.

Mankind could have gone on developing science without serious handicaps by the use of Newton’s laws; however, it appears that never would the whole scheme of the cosmos have been revealed in its simplest form without the new Einstein concepts. The chief drawback of the principle of relativity is that it cannot be visualized by minds of the three-dimensional world. Space is of three dimensions, Time being relative instead of absolute; we must consider it as well as the three dimensions of space. This is easy in mathematics, but a four-dimensional world cannot be conjured up in the mind’s eye. Nevertheless, this far-reaching principle, which has so far passed with flying colors tests that have been applied, is treated briefly in a later chapter. In the meantime, let us be assured that Newton’s laws can be safely depended upon for most practical and scientific purposes.

Galileo saw a chandelier swinging gently to and fro and he wondered why. Thousands had witnessed the same thing since the beginning of man, but few contemplated the phenomenon thoughtfully, as he did. Apples had dropped for ages, but Newton (if the apple story is true) was one of the relatively few to wonder why. Primitive men learned early in their lives that some things were heavy and other things were lighter. This downward force, which we term gravitation, was utilized in many ways even by early races. There is nothing spectacular in the force of gravity. Being commonplace and universal in man’s experience there is little wonder that it did not interest or was not even recognized by many persons as a great fundamental natural property of the Earth and of matter. So much more credit is due to those who did give their attention to it.

These discussions do not aim at historical treatment so no attempt will be made to go back to the first person who devoted study to this or that phase of physical science. In fact, it would be impossible in most cases to find a record of the first person. However, as a matter of interest and as an aid in presenting the various subjects somewhat in perspective, some of the early contributors of noteworthy data and analyses will usually be included.

Galileo (1564-1642) was born on the day of Michelangelo’s death. One might fancy that this signified the passing of the sceptre from art to science, for science was destined to receive a great impetus from this remarkable man. While still a youth he discovered the regularity of the vibration of a pendulum by observing the swinging of the cathedral lamp of Pisa. He set to work and found that the vibration of a pendulum varies as the square root of its length. He recognized the utility of the pendulum as a timing device, but it remained for Huygens (1673) and others to perfect its use in clocks.

Shortly after his first observations of the pendulum, Galileo conducted his famous experiments on falling bodies dropped from the leaning tower of Pisa. By showing that the velocity of descent was independent of weight, he upset the idea which had prevailed for centuries that the velocity was proportional to weight. Many who saw his objects of unequal weights, dropped simultaneously from the same height, strike the ground at the same time, still did not believe that Aristotle (384-322 B. c.) and his followers were in error. When we contemplate that civilization had been progressing for many thousand years, it is difficult to believe that only 400 years ago Galileo was for the first time proving before an audience, which for a time was still to remain skeptical, the law of falling bodies. To us this is a simple law, but Galileo, in proving by experiment and placing in proper mathematical relation to other factors the acceleration of a falling body, made a contribution to physical science comparable to all the work of the philosophers who preceded him.

He also studied the motion of projectiles under the two forces, the projecting force and that of the earth’s attraction. Then Galileo turned his attention more to the heavenly bodies. Learning of the telescope invented in Holland, he constructed one for himself and began a series of noteworthy observations. He discovered the sun-spots, the satellites of Jupiter, the rings of Saturn, and the mountains and other markings of the Moon. What fascination there must have been to gaze upon these marvels that had been hidden from man’s eyes for so long!

The stage was well set for the appearance of Kepler (15711630) who had a life-long struggle against poverty and ill health. Although he did not inherit the silks and ruffles that fell to Tycho Brahe, he did inherit great riches in the astronomical observations of his more prosperous predecessor. Kepler took up the Copernican theory of circular planetary motions, but was unable to reconcile the assumptions of uniform circular motion with the observational data available. He gave up the idea of uniform motion and also began to experiment with other closed curves. Finally he discovered that Mars describes an ellipse around the Sun and that the Sun was in one focus of the ellipse. This led to other conclusions which are known as Kepler’s three laws pertaining to the motions of the bodies of our solar system. They are,

1. The orbit of each planet is an ellipse, having the Sun in one of the foci.
2. The straight line joining a planet and the Sun describes equal areas in equal times.
3. The squares of the times of revolution of any two planets about the Sun are proportional to the cubes of their mean distances from the Sun.

It will be noted that the first two laws concern the motion of anyone planet and the third gives a relation between the periods and distances of the various planets. The determination of anyone distance in the solar system, therefore, makes it possible to determine all other distances, because the periods of revolution can easily be determined by observation. It has been stated by some authorities that in the entire history of astronomy only two other works, those of Copernicus and Newton, are of equal importance.

It is seen that in the earlier period of scientific development, astronomical observations were contributing much toward an understanding of the physical world. This was inevitable because these data were obtainable by direct observation. Much of our present knowledge of the electron, of radiation, and of atomic structure is obtained by indirect methods which naturally are the result of this period of greater knowledge. However, even now, observations of the stellar universe and of the phenomena taking place in stellar crucibles are contributing much toward the development of physical science.

Copernicus (1473-1563) developed the theory of circular planetary motions around the sun. When Copernicus was 19 years of age Columbus re-discovered America (for it had been visited by the Norsemen many years before). This lent proof of the rotundity of the Earth which was not fully proved “by experiment” until Magellan made his great circumnavigation. Shortly after this event, Tycho Brahe (1546-1601) was born of a noble Danish family. He became the greatest astronomical observer up to that time. It is said that he never went into his observatory for his night’s work without being attired in his best clothing. When asked why he wore his silks and ruffles he replied to the effect that as he gazed at those celestial bodies he felt that he was in the presence of his Maker. Indeed, he must have.

“One sun by day, by night ten thousand shine; And light us deep into the Deity;

How boundless in magnificence and might.” — Young