How They Trailed a New Planet (Jun, 1930)
This is a contemporary account of the discovery of Pluto. At the time it had not yet been named. The article lists Atlas, Prometheus, and Pluto as suggested possibilities.
How They Trailed a New Planet
Study of many photos of stars disclosed to a farm boy what may prove a new world where a famous astronomer said it would be. Old theories are upset by find.
ALDEN P. ARMAGNAC
A NEW planet has been announced. Out in space, four billion miles beyond the globe we live on, a yellowish object, a little larger than the earth, swings in a vast circle about the sun; a frigid little world, bathed in the dim light of perpetual dusk. Its discovery is called the most important event in astronomy in nearly a hundred years.
A new planet is not found every day. As many of us learned in school, a planet is one of the exclusive company of heavenly bodies that get their light and heat from the sun. They swing about it, as the earth does, in great circular paths, or orbits. These earthlike worlds are so few in number that they may be counted on the fingers.
Six, visible to the naked eye, were known to the ancients. In outward order from the sun they are: Mercury, Venus, Earth, Mars, Jupiter, and Saturn. Only two more, far-away Uranus and Neptune, were added comparatively recently when peering at the sky with telescopes came into fashion.
Now there is a ninth.
The ninth awaits positive confirmation.
It behaves differently from other planets. Its orbit is so far from a perfect circle, and tilted so askew, that astronomers hesitate to declare it a planet with certainty. Yet its actions are even less like any known comet, or anything else that might be mistaken for a planet.
There is one compelling reason to believe the newcomer is really the ninth planet. Astronomers of the Lowell Observatory, at Flagstaff, Ariz., found it remarkably near the spot where the late Doctor Percival Lowell, founder and director of the observatory, predicted it fifteen years ago. When Clyde Tombaugh, one-time Kansas farm boy who came to the observatory to study astronomy, spotted it as a flash of light on a photographic plate, the long search was believed ended.
Far away as the new planet isâ€”so far that its light, racing through space at 186,000 miles a second, takes six hours to reach our telescopesâ€”its discovery has practical significance for many besides the astronomers.
Even dictionary-makers and book publishers are upset by the discovery. At least two widely-used standard dictionaries felt safe in listing, to round out their definitions of “planet,” the names of the first eight, without such qualification as “so far known.” Now the dictionaries to be up to date must publish a new edition. Meanwhile, for a brief time, there are no complete books whatever on general astronomy. A New York publisher of school books told Popular Science Monthly that revised editions, probably available next fall, would describe the new planet.
Anyone who has ever had the curiosity to wonder where the earth itself came from is further concerned in the discovery of the new planet, for, astronomers say, it throws a new light on the way the earth was born. Its finding solves other long-standing mysteries of the heavens, tooâ€”for instance, wobbles in the motions of Uranus and Neptune, the two planets nearest to it, and strange delays of several days in the returns of Halley’s comet, a flashy periodic visitor to our sky.
Yet the planet itself is no easy object to see. Few Americans will ever see it except in photographs. It is far too faint to be seen in the night sky by the naked eye; or, for that matter, through anything short of a sixteen-inch telescope such as a large observatory would possess. Even that would require good “seeing weather.” Astronomers classify the planet as of the “fifteenth magnitude” in brightness, which would make it about a thousand times fainter than Neptune.
A concrete picture of this degree of brightness is suggested by Dr. Donald H. Menzel, of the Lick Observatory at Mt. Hamilton, Calif. If mountains, atmosphere, and the earth’s curvature did not intervene, astronomers at the Lick Observatory could see New York, 3,000 miles or so away, through their great telescope. Then, if someone stood on top of New York’s tallest building and held out a brick in his hand, the sunlight reflected from that single brick would appear about as bright as does the new planet in powerful telescopes. Another example of its brightness is that it corresponds to the light of a tallow candle seen at a distance of 430 miles, the approximate distance between New York and Cleveland, O.
When such an object must be picked out from among some 30,000,000,000 stars in the sky, many of them far brighter, it is no wonder that the world’s greatest observatories failed to notice it in the past.
It was picked up first at the Flagstaff observatory because Dr. Percival Lowell had built that lookout post and equipped the turreted dome for the sole purpose of finding it. This he did at his own private expense. He was sure of himself. Working with pencil, paper, and intricate equations, he had already “discovered” the planet, on paper, and predicted exactly where to look for it in the heavens.
How Dr. Lowell could locate so definitely a planet he had never seen is made easier to understand by the parallel case of Neptune’s discovery nearly a century ago. This was the second planet really to be “discovered” by astronomers. The first, Uranus, was a lucky find of Sir John Herschel’s, when in 1781 he swept the British skies with a homemade seven-inch reflecting telescope. But Neptune’s finding was a star-gazing feat backed by mathematics.
URANUS, once found, had failed to follow the eighty-four-year course around the sun that astronomers predicted for it. As if pulled by some invisible hand, it sped ahead of its expected itinerary until 1822; then it began to lag behind. The “invisible hand” was thought to be the pull, by gravity or tidal force, of some unknown planet beyond Uranus. “We see it,” Sir John Herschel remarked, “as Columbus saw America from the shores of Spain. Its movements have been felt trembling along the far-reaching line of our analysis with a certainty hardly inferior to that of ocular demonstration.”
It may have been that sincere, if high-sounding, declaration that spurred two men, unknown to each other, to tackle the formidable mathematics necessary to locate the unseen planet â€” John Couch Adams, in England, and U. J. J. LeVerrier, in France. Adams finished first, but British astronomers who sought the planet at the spot he indicated were too slow. In the meantime, one day in September, 1846, the Frenchman had sent this rather cocky message to Johann Gottfried Galle, an astronomer of the Berlin Observatory :
“Direct your telescope to a point on the ecliptic (the single plane in which all planets revolve about the sun) in the constellation of Aquarius, in longitude 326 deg, and you will find within a degree of that place a new planet, looking like a star of about the ninth magnitude, and having a perceptible disk.”
On the night of September 23rd, Galle looked. In half an hour he had found Neptune. LeVerrier was not thrilled. He knew that he simply could not be wrong. He never bothered once during his lifetime to look at his planet through a telescope. But the world hailed the addition of a new planet to the solar system.
NOW Dr. Lowell stepped into the picture. He was one of the first to point out that the new planet Neptune did not, as astronomers had hoped, explain all of Uranus’ outlaw conduct. It helped, but minor irregularities still remained. As early as 1902, Dr. Lowell declared he believed that still another planet, beyond Neptune, was responsible for these. In 1915 he published his figures which definitely located, in one of two possible positions at opposite corners of the sky, the unknown planet that was causing Uranus’ trouble. Undoubtedly it was troubling Neptune, which was nearer to it, even more. Little information on this point was available, though, since Neptune had completed only a fraction of its circuit around the sun since its discovery. That had forced Lowell to base all his figures on distant Uranus, making his feat all the more remarkable.
The figures were completed just in time, for Lowell died in 1916, the plane still unfound. But he had left an observatory and the best of clues. The search continued, encouraged by the belief of others in a new planet, notably Prof. W. H. Pickering, observer in Jamaica (P.S.M., Aug. ’28, p. 60).
Last year came another big aidâ€”the most powerful photographic telescope of its kind in the world, which looks more like a huge camera than a conventional telescope. Its thirteen-inch lenses were ground to an accuracy of better than one millionth of an inch.
It remained for a former farm boy to finish what Dr. Lowell had started. When this nineteen-year-old lad, with a hobby for astronomy, Clyde Tombaugh, graduated from high school at Burdette, Kansas, five years ago, his sister read a class prophecy naming him as the future discoverer of a new world. That prophecy was to come true.
Tombaugh, having successfully applied for a job at the Flagstaff observatory, sat one day last January in front of a “blink microscope,” examining fourteen-by-seventeen-inch photographic plates he had just taken of the heavens. The instrument he was using is one of the most modern aids to astronomers. Put in it two plates taken at different times of the same sky region, adjust them until they match perfectly, look in an eyepiece, and operate a lever. A flopping shutter hides first one plate and then the other. Stars, which are fixed in the sky, appear to stand still. But any object that moves or flickers, such as a comet or a planet, stands out like a beacon in contrast to the rest.
THUS Tombaugh had already examined, perhaps, a thousand slides. But now his practiced eye caught a flicker of something new. He stared into the eyepiece. It couldn’t be, but it was, the new planet.
“Excited? I should say so!” Tombaugh says. “What did the others say when I called them in to see it? Well, you know how these astronomers are. They are used to thinking in terms of millions of years, and millions of miles. They weren’t excited. They said it might possibly be the Lowell planet, but they would have to watch it further to check it with data they had been gathering.”
Seven weeks later Dr. V. M. Slipher, the observatory’s director, telegraphed to Harvard College Observatory, official center for astronomical news, the epochal announcement:
“Systematic search begun years ago, supplementing Lowell’s investigation for a trans-Neptunian planet, has revealed an object which, for seven weeks, has in rate of motion and path consistently conformed to a trans-Neptunian body at the approximate distance he assigned. Fifteenth magnitude; position March 12th, at three hours Greenwich Civil Time, was seven seconds of time west from Delta Geminorum, agreeing with Lowell’s predicted longitude.”
NOTE, if you please, the commendable reservation of the Lowell telegram. The astronomers did not claim to have discovered the trans-Neptunian planet. They simply stated that the object they had watched for seven anxious weeks had moved as a trans-Neptunian planet should. It might still be a comet, as some British astronomers suggested. The Flagstaff astronomers explained that they had made their announcement “only” seven weeks after sighting the planet simply to give other astronomers a better chance to look at it since it soon would be too low in the evening sky for further observation this year.
As the news flashed from the Harvard center, the great telescopes of the world’s observatories swung on their massive trunnions to converge at the point in the sky where the new planet had been discovered â€” in the star group or constellation known as Gemini. It was no light matter to disrupt the twenty and thirty-year schedules of star study that many observatories are following, even to sight a new planet; but this time, studies of stars, for the moment, were set aside. First the twenty-four-inch reflector of the Yerkes Observatory, at Williams Bay, Wis., picked up and photographed the newly-found member of the solar system. Hardly were the plates developed when Harvard Observatory flashed the news that it had snapped the planet’s likeness through its sixteen-inch refractor, by a ninety-minute exposure.
“AS A small but devoted homage to American astronomy,” Prof. Emilio Bianchi, director of the Brera Observatory at Milan, Italy, interrupted the important work of its Merate substation to order its powerful Zeiss telescope trained on the new planet. It secured at once two excellent photographs.
Astronomers are clever fellows at learning things about a world visible only as a small speck on a photograph. One rather startling thing they have found out about the new planet is that it seems to resemble the earth more than its nearer neighbors; its faintness suggests that it is solid rather than gaseous or liquid.
No life as we know it could exist on this frigid planet, far removed from the sun’s heat. Even on its sunny side, unless it has internal heat such as the earth manifests through volcanoes, its temperature must be 382Â° F. below zero. If our earth were transported there, its air would liquefy and fall to the ground, where it would freeze. Only hydrogen and helium gases would remain gaseous, and thus would be left for an atmosphere, in such cold as that of the new planet.
If any creature, of some sort utterly unknown on earth, were able to stand the cold, it would not live in total darkness, but in a sort of pearly dusk, midway between day and night. The sun, 4,000,000,000 miles away, would be hardly more than a pin point of light. Yet its glow would still be more than 200 times brighter than the earth’s full moon.
The new planet may have moons of its own. But unless the new planet’s moons, if any, are big ones, no telescope yet built could see them.
EVEN in the short time that the planet has been known it has made notable contributions to the science of astronomy. At the outset, it is the first of the nine planets ever to be discovered by photography. The new planet’s discovery practically doubles the known area of the solar system, or planet-family’s, back yard. Its extreme distance from the sun, some astronomers say, kills the old idea that the planets were born by condensation from rings of gas, as raindrops condense from a cloud. No ring could exist of such size as would be required by the new planet, they say, and therefore this old “nebular” theory seems doomed.
Another remaining duty, as this issue goes to press, is to give the planet a name. Curiously, astronomers have already used up many of the most appropriate names in christening the hundreds of asteroids â€” those tiny bodies, believed to be fragments of a single planet, that revolve between Mars and Jupiter.
This seems to rule out one name, Minerva, suggested for the planet but already given an asteroid. One suggestion was to name the new planet after its prophet, Dr. Lowell. But astronomers believe, from past experience, that only the names of mythological deities, such as those that other planets bear, will stick. Some suggestions so far recorded are Atlas, Prometheus, and Pluto. Other names are pouring in on the astronomers at the Flagstaff observatory, who probably will be entitled to select a name for their planet.
The name may be chosen by the time you read this, thus officially welcoming the newest comer into our family of planets. Who can say whether the future will bring more?