He Clocked the Cosmic Whirl
The story of the Canadian who solved the secret of the Milky Way and thereby became one of the world's most famous astronomers
THIS IS the story of a great Canadian, a one-time farm boy who became a machinist, graduated from university at the age of thirty-four, and now at seventy-two is one of the world’s ranking scientists, an astronomer whose achievements will be remembered so long as astronomy remains a science.
It is also the story of one of the major astronomical discoveries of modern times; the story of the .solution of one of the most awesome and elusive riddles the universe has yet revealed.
Plaskett of Victoria is the Canadian.
The Rotation of the Galaxy: the discovery.
Dr. John S. Plaskett, C.B.E., F.R.S., until two years ago was head of the Dominion Astrophysical Observatory at Victoria, B.C.—he retired at seventy. A world-renowned figure in astronomy, few Canadians had heard his name until he was made a Commander of the British Empire in one of Mr. Bennett’s honors lists. Even now he is little known in his native land, and yet his lectures at European centres of learning are important scientific events. What the American Philosophical Society thinks of him is indicated by the fact that it made him a foreign member at the same time it conferred this honor on Albert Einstein, the great mathematician.
And what is The Rotation of the Galaxy?
Call it the cosmic whirl, and you’ll not be far wrong. Described in its baldest terms, it’s simply the rotation of all the stars in the Milky Way system about a common centre. We earthlings with the sun, moon and planets are part of it.
The speed at our part of the whirl is about
600,000 miles an hour and it takes us about 200,000,000 years to make one round trip !
Quite a whirl !
The idea of a cosmic whirl had been discussed more or less vaguely down through the years, but it was not until 1926 that a Swede, B. Lindblad presented it as a definite theory. A few months later, a young Dutch scientist, J. H. Oort, of Leyden, suggested how theory could be tested by direct observation of star movements. Oort made some observations which
tended to bear out the theory but these were not regarded as final proof.
Plaskett furnished the conclusive proof. With J. A. Pearce, his assistant at the Victoria Observatory, he clocked 849 stars and not only showed that the cosmic whirl was an actuality but measured its diameter, its velocity, its period of rotation and its mass.
Which was quite a job for an ex-machinist; and which explains why Plaskett is now one of the world’s most famous astronomers. The next time you are out of doors on a clear, moonless night, take a look at the heavens. You will notice at once that the stars are not uniformly distributed. Some parts of the sky are much more thickly spangled than others. A great band or belt of stars stretches across the sky from horizon to horizon, in which the stars are so closely packed that it looks like an arch of pearly light. As everyone knows, this is the Milky Way. In nearly all languages it has the same name, and the Mexicans call it poetically, “The little white sister of the many colored rainbow.” From the Milky Way, then, comes our term, galaxy, derived from the Greek word ga laxius, meaning milk.
The number of stars visible to the unaided eye is usually grossly exaggerated, most people believing that there are millions, whereas it is only under exceptional conditions that more than 3,000 are visible at one time. But even the smallest telescope shows many times that number; and
through a larger telescope, literally millions of stars can be seen. However, no matter what the size of the telescope, the same curious phenomenon is apparent: the stars are several times more numerous in the direction of the Milky Way than they are at right angles to it. On the reasonable assumption that the stars are fairly uniformly distributed in space, this can only mean that they extend to much greater distances in the direction of the Milky Way, or that our stellar system or galaxy is shaped like a great flat disc.
Sir William Herschel was the first to make accurate observations of the distribution of the stars, and he stated 150 years ago that the galaxy was shaped something like a great grindstone, with a diameter more than five times its thickness. It was not until the twentieth century that much advance was made upon Herschel’s pioneer work. Now, thanks to the Plaskett-Oort-Lindblad triumvirate, it is fairly certain that the great grindstone of stars has a diameter of 100,000, and a thickness of about 10,000 light years.
As Dr. Plaskett says, it is not easy to get an adequate conception of the immense distances thus glibly stated. A light year is the distance which light, moving at a speed of
186.000 miles a second, travels in a year; that is, six million million miles—a distance impossible to visualize. Put it this way: It has been estimated that two pounds of spider web would stretch around the earth, a distance of 25,000 miles. At this rate it would take 250,000 tons of spider web to stretch the distance of one light year, and hence about twenty-five billion tons to span the great grindstone known as the galaxy !
It is this great disc-like conglomeration of stars, some 100 billion in number, it is estimated, that Dr. Plaskett and his fellow scientists have shown to be rotating about a common centre. Our sun is only an average-sized star of all these billions, not at, or even near, the centre of the galaxy; and we, on the earth, are only a mere appendage of the sun, tagging along in the procession. The diameter of the system is about 100,000 light years. The sun is only about
15.000 light years, or a third of the way, in from the edge of this disc of stars, and hence 35.000 light years away from the centre. So gigantic is the sweep of the great wheel round its centre, that the sun, although it travels 2,000 times as fast as the fastest airplane—180 miles a second, or 600,000 miles an hour—makes the round trip only once in 200 million years.
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Outside our own stellar system, or galaxy, which is the only one we can see with the naked eye, there are innumerable myriads of other stellar systems or galaxies, separated from each other and from our galaxy by about a million light years of apparently empty space. That’s another story, however; here we’re concerned only with our own galaxy.
ONTRARY to the popular conception, ^ an astronomer is not a man who spends his life peeping through a telescope. The technique of modern astronomy is largely photographic. Light waves from a star can be analyzed by an instrument known as the “spectroscope,” in such a way as not only to tell us what the star is made of, but how fast and in what direction it is moving. These analyses are recorded photographically.
It is possible to measure star motion in two directions. These are called its radial motion and its transverse motion. Radial motion is the movement of the star toward, or away from, the earth. If a star is moving toward the earth, the wave length of its light is shorter than it would be if the star were stationary, just as the pitch of a locomotive whistle is higher if it is approaching you at high speed than it would be if the locomotive were standing still. Similarly, movement of the star away from the earth tends to lengthen the wave length of its light. These changes in wave length are recorded by the spectroscope by a shifting of the lines in the spectrum; and it is by measuring the photographed record of these “shifts” that the astronomer measures star velocity. The transverse motion, sometimes called proper motion, is simply the movement of a star across the sky which can be measured by direct observation. A combination of these two motions gives the direction in which the star is travelling as well as its speed.
Proper motions of stars have been measured for more than two hundred years; radial motions for fifty. But until the turn of this century, the more star motions that were measured, the more hopelessly random seemed their movements.
Order From Chaos
A BOUT THE beginning of the present
century, however, some trace of regularity began to appear. There was a certain community of motion running through the random speeds and directions, as if the galaxy consisted, not of a single swarm of stars but of two swarms, interjjenetrating one another like a swarm of mosquitoes around the heads of two people passing one another. It was only by careful analysis that this “star streaming” was discovered, but instead of clearing up the riddle of the random stellar motions, it at first only increased the confusion. And the puzzle was by no means lessened, when, about 1920, another kind of streaming was discovered. All “high velocity” stars, those with speeds greater than about fifty miles a second, were found to be moving toward one hemisphere of the sky—another puzzling phenomenon, somewhat analogous to “star streaming,” but even less amenable to explanation.
The first clue to the mystery was given by a young Swedish astronomer, Lindblad, working in his observatory at Stockholm. Ten years ago he resurrected the old spoliation of the rotation of the galaxy, but revolutionized it into harmony with modem knowledge, and developed a
theory which satisfactorily explained not only the great flattened form of our system, but also the curious systematic motions of “star streaming” and high velocity stars. He claimed that, just as in the solar system, where the rotational motion of the planets is maintained by the gravitational force of the sun, so the rotation of the stars and the sun around the centre of the galaxy is maintained by the gravitational force due to the whole system acting as if concentrated at the same centre.
Although a beautiful and orderly conception of the motions and structure of the galaxy, and an explanation of the mysterious systematic motions of the stars were provided by Lindblad’s theory, it did not indicate how the theory could be directly tested by observation—a very necessary procedure before any theory can be accepted. The necessary method was provided about a year later by a young Dutch astronomer named Oort., who further mathematically developed Lindblad’s work and showed how the rotation could be tested from the motions of the stars. This follows from the gravitational effect in a revolving system whose mass is unevenly distributed and is concentrated toward the centre of the system. Under these conditions those bodies nearer the centre move faster than those farther out. This is the way our own solar system behaves. Mercury which is closest to the sun travels in its orbit at a speed of thirty miles a second, the earth at eighteen, Jupiter at eight, and Neptune, which is farthest out, at three miles a second. Similarly, if the galaxy is rotating, stars nearer the centre of it will be moving fastest, and those nearest the edge, slowest.
This leads to a peculiar effect which can best be explained, perhaps, by an analogy. The only way in which we can detect the movement of the stars in the system is by observation from the earth. But the earth with the sun and the rest of the solar system is also rotating with the galaxy. We observe, therefore, from an observatory which itself is moving.
Now imagine a three-track railroad running in a circle with one train on each track, all moving in the same direction. The train on the inside is moving fastest, that in the centre at a medium speed, and the one on the outside at a slower speed. We are on the middle train and observe the other two. At intervals the inside train will pass us and as it draws ahead we will see it moving away from us, even though we are both travelling in the same direction. Ultimately it will get around to the opposite side of the circle and then it will seem to us to be travelling in the opposite direction.
Similarly with the outside train. As we overtake it, we say it is moving toward us; after we’ve passed it, it is moving away from us.
In relation to the rest of the galaxy we earthlings occupy the position of passengers on the middle train. The stars inside us in the whirl seem to behave as the inside train did;-the stars outside us, as the outside train.
Oort applied this reasoning to the radial motions of distant stars and showed that their motions were what might be expected if the galaxy were rotating in the manner described. Because of technical reasons which we need not go into here, observations had to be confined to very distant stars to minimize the chances of error. But the numbers of very distant stars available to Oort, with his limited equipment, were too small to make the proof convincing, and the provision of a much greater number of observations of the far distant star velocities was necessary before the great problem could be satisfactorily solved.
And here it was that the farsighted Canadian, Plaskett, stepped into a contingency that he had foreseen as long ago as 1911, when, working in the observatory at Ottawa, with its fifteen-inch telescope, he had started a campaign lasting until 1917, to persuade the Government to build a telescope large enough to put Canada on the map, astronomically speaking. Eventually it materialized in the great seventy-two-inch instrument in the observatory near Victoria, B.C., the largest in the world at the time of its erection.
From their vantage point in the brilliant aluminum-painted observatory on "Little Saanich Mountain.” which commands a view of the whole southern corner of Vancouver Island, Plaskett and his coworker, Dr. J. A. Pearce, made observations of 849 of the most distant stars especially suited for testing the rotation of the galaxy. These completed observations led to a conclusion that had been no more than speculation for over a century— that the galaxy rotates about a very distant centre in the direction of Sagittarius, a “star cloud” which forms the richest, brightest part of the Milky Way.
To realize just how microscopic we are in the great scheme of the universe, one has only to compare the figures. The solar system, of which the earth is such a tiny part, measures 10,000 million miles in diameter, yet it is only one six-millionth of the size of the whole galaxy. In other words, the galaxy or star system is sixty million times the size of the solar system.
Not only was Dr. Plaskett responsible for the final tracking down of the greatest problem the universe has yet presented, the ^Rotation of the Galaxy,” and its exact dimensions, but he added yet another piece of invaluable information to man’s knowledge of the mysterious universe. He was largely responsible for development of the theory of what is known as “interstellar” matter—an extremely tenuous, or thin, gaseous substance which fills the space between the stars. This gas is so thinly distributed that the whole volume of the earth’s sphere, which is 8,000 miles in diameter, would only hold four ounces of it.
Through the Canadian scientist’s efforts, it is known that there are present in the galactic space, calcium, sodium, and other elements, in the form of atoms, the smallest indivisible particles of matter. There are also dust particles, which look very much like wisps of smoke, and which have the effect of dimming the light of the stars. This inter-stellar substance—that, is, the calcium, sodium and other elements— exists at an extremely high temperature— about 20,000 degrees Fahrenheit—which is produced by the total radiation of heat from all the stars in the galaxy. Its discovery has been highly important in the progress of science. It not only gives a dearer idea of the dimensions of the galaxy, explaining in a measure why comparatively close stars only show dimly, but
it has led to a theoretical work by another famous scientist. Sir Arthur Eddington, which sets forth an absolutely new idea of the properties of space.
It would be the zenith of earthly fame for any ordinary man to have two of the largest stars in the heavens named after him, but it is only one of the minor incidents in Dr. Plaskett’s record. In 1921 he discovered the most massive stellar system then known. Hitherto uncharted in the map of the heavens, they were double, or twin stars, more than 160 times the mass of the sun. They rotate around each other, even though they are fifty-five million miles apart, taking fourteen days for each circle. They were christened upon their discovery, and have since been known as, the “Plaskett Twins.”
Having digested all these astounding findings concerning the. scheme in which he lives, the average “man in the street” is inclined to ask, in the expressive modem vernacular, “So what?” To which Dr. Plaskett replies:
“So far as practical results are concerned, the demonstration that the galaxy is rotating about a distant centre in some 200,000,000 years has at present certainly no economic value. But it lias equally certainly a great ethical and cultural value, by further satisfying man’s instinctive craving to discover the reason for the phenomena he sees all about him in nature, to explore the mysteries of the universe. It is mainly by the researches and discoveries of science that civilization has advanced from primeval times to the present.
“But to the scientist, one of the greatest satisfactions of such discoveries is in establishing still further the reign of law and order in the universe, in showing how what had previously appeared as inextricable confusion yielded to man’s perseverance and skill and became a beautifully ordered system obeying the universal laws of nature.”
A Self-made Scientist
AND WHAT of this man whose vision sweeps within its breadth all the workings of the universe, and whose human experience has run the gamut from small beginnings to the peak of human achievement? His own story is hardly less fascinating than the one he has unfolded from the stars.
Although he matriculated from the Collegiate Institute at Woodstock at the early age of fourteen, until he was twenty the premature death of his father kept him at home on the little Ontario farm. Then he studied the machinist’s trade in Woodstock for three years, after which a jobhunting expedition through the State of New York secured him a position with the Edison Electric Company at Schenectady — (he original firm of the General Electric Company—and eventually he arrived at
Sherbrooke, Quebec, with the company’s Canadian branch.
Pie married in 1892, after filling the post of applied mechanician and laboratory assistant at the University of Toronto for two years. Then, as Dr. Plaskett says with a directness that marks all his conversation, it was his wife’s encouragement and enthusiasm that persuaded him to forget the lapse of years and start his studies at the university. Doing his laboratory work by day and studying till midnight, he worked day and night for six years—two years for a second matriculation and four years for a degree, finally graduating in Ï899 at the age of thirty-four, with firstclass honors in mathematics and physics.
It was in 1903, after four years as lecturer and experimenting in scientific photography at the university—which last interest has been more or less of a hobby all his life and invaluable in his career—that the young scientist received his first official appointment in astronomical work from the Astronomical Department of the Interior at Ottawa. In 1909 he completed a series of observations for spectroscopic determination of the solar rotation which formed one of the standard researches on the problem. Pie initiated the measurement of radial velocities at Ottawa, and carried it out so efficiently that it was said by fellow astronomers that the fifteen-inch telescope did the work of a twenty-five-inch instrument in his charge.
Recognition was not long in coming, and in 1910 he went as Canadian representative to the meeting of the International Solar Union at Pasadena, where he more clearly saw the need of better equipment if Canada was to appear at all in the field of astronomy. Pie had done such outstanding work with his meagre equipment at Ottawa, that he easily received the backing of all his fellow scientists in his campaign for a new instrument.
Dr. Plaskett still maintains that, in spite of all his astronomical laurels, his greatest contribution to science was the capturing of Dominion Government funds for the erection of the 72-inch telescope in the observatory near Victoria. After years of effort, it was finally clinched only when he abandoned his heavenly highroads and spent three months in the Parliamentary lobby at Ottawa. Although this instrument was followed two or three years later by a 100-inch one at Mount Wilson, Pasadena, and more recently by a seventy-four-inch telescope at Richmond Hill, Toronto, the Victoria observatory set a new standard of accuracy and efficiency, and the results of work done there by a staff of seldom more than four members, have been relatively prolific as compared with observatories elsewhere, while it still holds the record, almost unequalled, in determining the radial velocities of the stars.
The astronomical branch of the Dominion Government was instituted only fifty years ago, when the need arose for the determining of 1,500 miles along the 49th parallel, for the boundary between Canada and the United States. Then the branch was used mainly for astronomical work connected with the surveying of the Western provinces, determining the meridians and parallels from which the boundary lines were subdivided. In 1905 the department developed into the observatory at Ottawa, where the fifteen-inch telescope was introduced for the first astronomical research attempted in the Dominion. Dr. Plaskett soon found this too small to carry the observation of the fainter stars and for coping with the illimitable possibilities he foresaw in the scientific future.
So it is that, owing to the vision and perseverance of one man, Canada, a new country with an astronomical history of only fifty years and comparatively few scientific resources, holds a leading position in astronomical research, and has participated in one of the major scientific discoveries of modem times.