Tales from the Golden Age: Clyde W. Tombaugh; Discoverer of Pluto.

Clyde W. Tombaugh pictured here with his homemade long focus 9 inch Newtonian reflector.


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Can it be a coincidence that many of the most pre-eminent amateur astronomers to emerge in the United States during the early 20th century were born into rural communities? We have already seen some of the work of the late Sky & Telescope columnist, Walter Scott Houston, who was born and raised in Tippecanoe, Wisconsin. Then there is Leslie Peltier, the great comet and variable star observer, who lived his entire life among the strawberry fields of Delphos, Ohio. And that list wouldn’t be complete without Clyde W. Tombaugh, who hailed from a farmstead seven miles from the town of Streator, Northern Illinois. In this vast open country, where fields would stretch from horizon to horizon, the glory of the night sky would have been made manifest to their young, curious eyes, stoking an early passion for all things astronomical.

No; there are no coincidences, only convergences.

These great American amateurs all started out with humble beginnings. Life was hard, very hard by modern standards, but ultimately rewarding. It was into this kind of world that Clyde W. Tombaugh was ultimately thrust. The first born and eldest son of Muron (born 1880) and Adella Tombaugh, Clyde entered the world on February 4 1906. For a few generations, the Tombaughs were distinguished from many other families in their rural community in being an educated bunch. Clyde’s grandfather was University educated and served as a school teacher. His father too had high ambitions to follow a career in mechanical engineering but the circumstances of his early days meant that there were many stops and starts in his education, with the result that, although he attended the local University of Illinois, he never completed his degree. More children arrived in rapid succession to Clyde; first Esther, two and half years his younger, and then Roy, Charles, Robert and finally Anita. Such a large family demanded an industrious bread winner and Muron did his Sunday best for his family, running a busy rented farm which eked a modest income from the cultivation of oats, wheat and corn. He also singlehandedly managed a threshing company which catered for the local farming community.

Being the eldest in the family, Clyde quickly became like a second father figure to his younger siblings and helped look after them when his parents were preoccupied with other matters. By all accounts Clyde’s elementary school days were happy and productive and he was lucky enough to have teachers who encouraged the boy’s natural curiosity. He excelled at history and geography. But his transition to high school was marred by a particularly vicious bout of whooping cough, which left young Clyde bedridden for a few months, and as a result he fell behind with his studies. After school, he was expected to help out on the farm, planting seed beds, cultivating, harvesting and threshing crops as they matured in their appointed time. In those days before mechanisation, work days on the farm could be were very long, often lasting from seven in the morning until 6 in the evening. In these ways, Clyde’s early life was no different to many thousands of other youths, especially since many late teenagers had enlisted in the U.S. army between 1917 and 1920.

In high school, Tombaugh enjoyed the elementary courses in physical science and biology and in his spare time he’d often be found reading into the night, with only a kerosene lamp for light. He reputedly read and studied the Bible from cover to cover; quite a feat for such a young man and which had a lasting effect on him, right on into old age. He also borrowed his father’s old books on engineering mathematics and even dabbled in some ancient Greek and Latin. Clyde’s interest in astronomy was piqued by his paternal uncle, Lee, who’s family lived and worked on a nearby farm and who cultivated a life long interest in astronomy. Lee was the proud owner of a 3 inch singlet (read non achromatic) refractor giving a fixed power of 36 diameters. While the optics on such a telescope were understandably so-so, they did give good views of the lunar regolith, which mesmerised young Clyde.

Responding to Clyde’s growing interest in astronomy, Muron and Lee chipped in to purchase a new and in many ways, more serious telescope; a 2.3 inch aperture long focus achromatic refractor offered by Sears Roebuck & Co. (an early U.S. based department store), which was equipped with a single ocular delivering a power of 45x. That telescope enjoyed a very long and productive life. In those early days, the Sears family telescope alternated between his home and his uncle Lee’s. It was with this telescope that Clyde enjoyed his first decent view of Mars during a favourable opposition, where it showed a few dark markings and the polar ice cap. By now, Tombaugh had been enthralled by some pamphlets circulated by the Tennessee amateur, Latimer J. Wilson, who owned a magnificent 11 inch reflecting telescope with which he began to draw the canals of Mars, sensationalised by the late Professor Percival Lowell and the Italian astronomer, G.V. Schiaparelli.

In 1922, the first upheaval in Clyde’s life occurred when the family crops failed. Seriously strapped for cash, the Tombaughs were forced to move to Burdett, Kansas, where Clyde’s uncle Lee had recently moved to manage a 250-acre property. He found the move especially stressful though, as he had forged a very strong bond with his first cousins who lived in Streator. Then in 1924, Clyde suffered a particularly nasty fall while pole vaulting which all but ended his keenness for athletics and football. After graduating from Burdett High School in 1925, he considered enrolling at the local University of Kansas but had to save the money to pay for his University fees. Apart from his work helping out on the farm, Clyde’s desire to make a serious sized telescope grew ever more strong, and with the help of some books and magazine articles, he ordered up the materials to make a long focal length 8 inch reflecting telescope from scratch. Completed in April 1926, it had a focal length of 84 inches, which he had intended to mount inside a long wooden tube and mounting with two setting circles (also of wood) to assist in pointing the instrument. All that was left to do was to get the mirror blank silvered. Since he did not have the chemicals at hand to do the silvering, he entrusted the mirror to a telescope maker, a one Napoleon Carreau, who had set up a business in Wichita about 140 miles away.

Mr. Carreau did the lad a favour and had the mirror tested prior to silvering. And what he found didn’t exactly inspire; the mirror was badly figured and would not yield the good high power images Tombaugh had hoped it would. Needless to say, the returned mirror with attached note from Carreau left Tombaugh gutted. But thankfully, he didn’t give up. Instead, he vowed to build his very own testing area for any future mirrors he would grind. And it was there and then that Tombaugh plotted an ingenious scheme. He would ask his father for help in the construction of a so called “cyclone cellar” an underground storage area for foodstuffs and a safe haven to take refuge in the event of a tornado strike. His plot worked! After the all important harvest of 1926, with no bull dozers to call upon, Clyde had to dig his own hole; and an enormous one at that; some 24 feet long  by 8 feet wide  and 7 feet deep! He enlisted the help of friendly neighbours to pour 540 cubic feet of concrete to complete the structure replete with floor, walls, windows and even an arched staircase! When completed, this new cellar served as the ideal place to perform testing on his future mirrors, as the air circulating within it was always cool and rather uniform in temperature.

His next mirror, a 7 inch, was made for his uncle Lee, and when tested by Carreau, was found to be rather good! Auspiciously, Comet-Winnecke 1927 VII was ripe for observation, reaching a conspicuous magnitude of +3.5 at the time Tombaugh turned the telescope upon it. Lee was most impressed with the new instrument and immediately bought it from him. With these new funds, Tombaugh began thinking about a personal telescope; an instrument that might allow him to see the great showpieces of the sky and perhaps contribute his own findings to planetology. So in August 1927, he purchased the glass blanks to begin work on this third telescope; a 9 inch Newtonian reflector (featured above) with a focal length of 70 inches (so f/7.8). Grinding the mirror was not without its problems however, for as soon as he got rid of one zone up popped another but he kept working on through the winter and by the spring of 1928 Tombaugh was eventually able to obtain a very smooth figure with an accurate paraboloid, allowing the mirror to sustain very high powers (of the order of 400 diameters), so good enough for all applications he would use it for. By the autumn of 1928, the telescope was ready for first light and with a great sense of excitement he turned it on mighty Jupiter to see how it performed. Well, he needn’t have worried; Clyde watched in sheer amazement as its various markings were seen to drift across the disk. Turning next to Messier 13, the great globular custer in Hercules, he saw a storm of well resolved stars where his little Sears only registered a fuzzy blob. Clyde Tombaugh had realised his dream of owning a serious telescope. Indeed, it was so good that Mr. Carreau offered him a job as a technician in his Wichita workshop. Things were beginning to look up for the enterprising young squire from the back of beyond.

Despite the sheer elation he must surely have felt in designing and building his dream ‘scope, 1928 would not be a year Tombaugh would forget for completely different reasons. Earlier that summer, on June 20 to be precise, disaster struck the Tombaugh farm. A violent thunder storm wreaked havoc with the wheat and oat crops that were, until then, doing so well, owing to a warm spring. In the space of a quarter of an hour they lost it all! And it was so localised that the neighbouring farms went completely unscathed! It was a cruel twist of fate that there and then ended Tombaugh’s ambitions to attend college. It also meant his father had to put off buying that all important combine harvester that would have made life better for everyone. One thing was clear; Tombaugh had had enough of farming. Time to pursue something else.

By the end of 1928, Clyde had amassed an impressive portfolio of planetary drawings and he mailed a selection of them to Lowell Observatory, together with a letter explaining that he wished to be a professional astronomer and inquiring about how best he might go about becoming one. He must have made quite an impression, for what happened next was not only unexpected, it was downright music to his ears! As luck would have it, the administrators at the Observatory were looking for a keen amateur astronomer in good health who would assist in the operation of a new photographic telescope that would shortly be installed there. Needless to say, it set his heart racing!

It was make your mind up time; either become some obscure telescope maker or get a chance to become an astronomer at his favourite Observatory. It was a no brainer! He would accept the post at Lowell, on the understanding that he was to be employed for a trial period of 10 months before being offered the post on a permanent basis. What is more, with a guaranteed monthly salary of $125, he was now earning more than he ever could while working on the family farmstead.

Tombaugh, however, would have to find the means to fund his 1,000 mile rail journey to the American southwest, as well as his initial stay, but he continued working like a Trojan throughout the summer and autumn of that year, operating a combine on a neighbour’s farm, and that earned him the additional cash he badly needed. So, on the morning of January 14 1929, after saying goodbye to his family, he mounted the couch car and settled in for the long, 28 hour journey ahead. As the train pulled off, he must have felt very sad to leave his family, especially since his mother was about to give birth (within 12 hours actually) to the youngest member of the Tombaugh family; little Anita. Indeed, he would not lay eyes on his newly arrived sister for another six months!

Tombaugh, of course, had no idea what was in store for him at Lowell Observatory. What would he be working on? Would he live up to expectations? Would he enjoy the work? All of these questions must have flashed through his mind as the train ventured further and further away from Kansas. Little did he know that he would be getting involved in the hunt for a new planet, long since predicted by the mathematical astronomers who had deduced the presence of a world beyond the orbit of Neptune, based on perturbations in the orbits of the outer planets. And little did he know that this search commenced a full year before Tombaugh was born!

Professor Lowell, deeply depressed by the ridicule he had received for advancing his far fetched idea of an intelligent race of Martians, desperately needed to restore credibility to his work and the status of the Observatory he founded. So in 1905 Lowell spearheaded a new search for Planet X and began acquiring astrographs that would enable a systematic search to be conducted at Mars Hill. By 1912, he had borrowed a state of the art wide angle camera with a 9 inch lens from Swarthmore College’s Sproul Observatory, but after his untimely death in 1916, the camera had to be returned to its rightful owners. Unbeknown to Lowell and his well trained staff, that same camera actually recorded the mysterious planet in a series of exposures captured on March 19 and April 7 1915, but this would not come to light until many years later.

When he arrived at Flagstaff station, he was met by Dr. Vesto M. Slipher, who escorted him by car out of town and up to Mars Hill. As they began to ascend in altitude, he would see the Ponderosa pine trees following the contours of the winding road, now covered in winter ice. Indeed, it was from these pine trees that Lowell built the dome to house the great 24 inch Clark refractor which formed the centre piece of the famous Observatory.

The Clark Telescope Dome on Mars Hill. Image credit: Wiki Commons.

When they arrived, Clyde was introduced to the staff on duty that day; Drs C.O Lampland, E. Pettit and S.B. Nicholson and the Observatory’s handy man, Mr. Jennings. Dr Slipher provided Tombaugh with the details of his job description; he was to operate the new 13 inch f/5.3 astrograph to resume the hunt for Planet X which had come to a halt back in early July of 1916. A smaller 5 inch astrograph was piggybacked atop the main instrument and it took exposures of precisely the same region of sky as the larger astrograph. Indeed, as we shall see, this smaller instrument played an important role in Tombaugh’s seminal discovery.

After the introductions were over, Jennings gave Clyde a lift back down the hill for a spot of breakfast, and in the afternoon Tombaugh would be introduced to the instrument that would soon make him famous; the heavily mounted 13 inch astrograph ready for operation, except for one important detail; it was still without its lens. Indeed, this would not be installed until the middle of February. Designed by Carl Lundin, chief optician to the Alvan Clark & Sons telescope firm, it was a triplet objective designed to capture wide field images of the sky. It was exquisitely well made; one element had very strong curvature which made it very expensive to make, but after it was carefully loaded off the Model T truck, unpacked and mounted, initial tests could be conducted on its imaging potential. A few days later, everything was ready to enable it to take its maiden exposure. The astrograph was pointed at the Sword Handle of Orion and a 30 minute guided exposure conducted. Slipher, Lampland and Tombaugh were present that evening at the telescope. After exposing the photographic plates it was clear that the instrument was working well. The stars were pinpoint sharp, right across the field. Slipher must have let out a big sigh of relief; this expensive piece of kit would be more than capable of detecting Planet X; if it existed, that is!

The 13 inch f/5.3 Lawrence Lowell astrograph featuring the Lundin triplet objective used to conduct the search for Planet X. Image credit; Wiki Commons.

Tombaugh continued his training with the 13 inch astrograph for a couple of months, during which time he sorted out a number of mechanical bugs that might have otherwise jeopardised the entire project. By April 6, it was ready to go.

As one can imagine, finding such a planetary body amid the myriad stars captured by such photographic means was very much akin to finding a proverbial needle in a haystack. The search was confined to a narrow swathe of sky centred on the zodiac, beginning in Cancer but then carrying on the search into Gemini and Leo, and so on. And while each plate typically recorded the spurious disks of hundreds of thousands of stars, it was a great blessing in comparison to the prospect of having to comb through the blizzard of stellar bodies residing closer to the main body of the Milky Way, where stellar population densities shot up to greater than a million per plate in comparison. The strategy adopted by Dr. Slipher was to employ an ingenious device called a blink comparator, invented in 1904 by the German physicist, Carl Pulfrich, working for the famous optics firm, Carl Zeiss Stiftung. The instrument permitted rapid switching from the viewing of one photograph to another, “blinking” back and forth between the two images taken of precisely the same area of the sky but at different times. This allowed the user to more easily detect objects in the night sky that changed position. Of course, other objects besides planets were well known to move relative to the background stars; asteroids, for example. Many of these ‘interlopers’ were to be expected, of course, but they could be weeded out by a consideration of how much they moved in a given time interval. The velocity of a body orbiting the Sun depends on its distance from the Sun. The further away the object lies, the slower its orbital velocity will be and thus the smaller the distance it would be expected to move on a photographic plate.

Because most asteroids reside between the orbits of Mars and Jupiter, they will have a very well defined distribution of velocities all of which correlate with the distance moved on the photographic plates. Objects residing beyond the orbit of Neptune will have correspondingly smaller orbital velocities and will thus show much less relative movement on the photographic plates. So, Tombaugh was trained to look for movements in a certain size range per unit time (of the order of a few millimetres over the course of a week). That said, there were many other sources of error to consider, including the length of exposure of the plates, the effects of atmospheric refraction, dust, clouds, the spurious results attributed to variable stars, as well as false positives owing to defects with the emulsion (equivalent to CCD ‘blooming’ in contemporary digital imaging). In addition, great care had to be made to match the centres of each plate taken at a given time interval.

The Zeiss blink comparator used by Tombaugh with the 13 inch Lowell Astrograph. Image credit: Wiki Commons.

In addition to all of the above parameters, the frequency of blinking had to be fine tuned for optimal results. This was found to be about 3 Hz (i.e. 3 times per second).  Anything greater than 10Hz would introduce an effect known as ‘persistence of vision’, where the eye would start to register considerably less motion. Less that 2Hz and the time realistically needed to conduct the searches would have to have been greatly increased. In this way, every inch of these plates were to be examined microscopically, requiring great concentration to carry it out effectively.

In consideration of all of this, Slipher was acutely aware that the odds of success were still very low and, as a result, the staff were told to keep ‘schtum’ about the details of the project, for fear of more ridicule from either the gallous press or the greater scientific community. Indeed, this much was acknowledged by Professor Lowell at the outset of the project, and he accordingly encouraged his staff to pursue other avenues of research so as to shore up the amount of ‘conventional’ data produced by the astronomers on Mars Hill. Overall, Tombaugh conceded that his new post was far from glamorous. It required long hours, and 100 per cent commitment in sometimes freezing conditions that would tax the hardiest soul.

On bright, moonlit nights, no exposures could be made, and Tombaugh was therefore free to catch up with other duties, ranging from the mundane but no less essential, such as stoking the furnaces with logs and shovelling snow, to the specialised, like mounting and developing the photographic plates, operating the blinker and keeping detailed written records of events as they unfolded, and so on. There was also time for leisurely observing. One of the treats Clyde enjoyed during these moonlit spells was the use of the great refractor for the visual inspection of the planets. Though V.M. Slipher was a formidable theorist and spectroscopist, he was also a highly skilled visual observer, having conducted many years of observations through the 24 inch Clark.

Records show that he would regularly employ a yellow filter at the eyepiece to supress the secondary spectrum produced by the achromatic doublet lens while observing Mars at high power. Others preferred red or orange filters but Slipher felt the transmitted yellow light preserved the natural colours of the planet best. Typically powers were kept below 500 diameters for planetary work on the great refractor (double star mensuration would often require more but the instrument was not used for such work, at least during the time Tombaugh was at the Observatory). It was through his in depth discussion with Slipher that Tombaugh learned that Percival Lowell was accustomed to stopping down the aperture of the 24 inch to 16 inches some 90 per cent of the time it was being used! Tombaugh also practiced this technique rather often with the large refractor but he recalled many occasions where he saw the alleged canals, more or less, as Lowell and Slipher had recorded them. But he also added that when he finally had a chance to examine the Red Planet through the considerably more powerful 82 inch reflector (dedicated in 1939) at McDonald Observatory, Fort Davis, Texas, where the seeing conditions were often better, the canals disappeared into a series of dots that the eye would naturally try to join in a smaller instrument. Tombaugh most certainly knew that Lowell’s canals were a sweet illusion.

Percival Lowell at the 24 inch Clark, conducting daylight observations of Venus. Image credit: Wiki Commons.

It is also noteworthy that Tombaugh did not revere the great refractor, or any other kind of  telescope for that matter. Indeed, one biographer noted how Tombaugh would frequently argue with the other staff astronomers that a Newtonian reflector could equal or exceed the performance of the best refractors, and without generating a colour error. His peers were biased though, as they only had the 42 inch reflector at Lowell Observatory to compare the great refractor with; and that was hardly a fair comparison as it was badly mounted below ground and as a result suffered from inferior seeing more frequently than the refractor! Indeed, the conclusion reached by Tombaugh was also arrived at by the late Professor E.E. Barnard, whilst comparing the planetary images garnered with the great 36 and 40 inch Clark refractors, with which he was intimately acquainted, to the newly arrived 60 inch reflector atop Mount Wilson, which saw first light in early December 1908.

The morning of February 18, 1930, was rather overcast while Clyde went about his routine work at the Observatory. This morning he was comparing two plates, each consisting of 10 minute exposures, taken near the star Delta Geminorum; one dated to the evening of January 23 (no. 165) and the other, to January 29 ( no. 171) 1930. Loading the plates into the blink comparator he noticed a shift in position of a body that looked very promising. It had shifted by 3.5mm; in the ballpark of the trans Neptunian object. But he wasn’t getting excited just yet. Tombaugh was far too cautious to jump to any conclusions before he carried out his battery of checks. Was it a blooming artefact?  Was it a variable star? Was one plate overexposed relative to the other? All of these had to be investigated but sure enough, the object looked solid. Now he was getting excited but still doubted himself. Then he thought of the smaller 5” astrograph, which should have recorded the same phenomenon. So he had those plates exposed and though the images were considerably fainter, his microscopic examination showed the same blinking! A tingle ran down his spine as he contemplated the evidence; he was now 100 per cent sure that he had discovered Planet X.

Now he had to tell someone.

Dr. Lampland was working in his office adjacent to Clyde’s. Later he would recall that something seemed amiss that morning as the sound of the blink comparator fell silent for a good half an hour. Tombaugh shuffled across the corridor and knocked on Lampland’s office door. “Come in,” Lampland shouted. Quietly opening the door, Tombaugh popped his head round and said, “I think I’ve found Planet X!” With this, Lampland jumped out of his seat and darted across the corridor to check the data for himself. As Tombaugh described the drill of checks he had carried out, Lampland looked very impressed. It was time to inform Dr. Slipher. So, excitedly, Tombaugh made his way down the long corridor leading to his office. “Dr. Slipher,” he said, “I have found your Planet X.” With a lingering stare, Slipher charged out of the office to examine the evidence for himself. For another hour the three men poured over the data and all were in agreement that it was a bona fide world beyond the orbit of the 8th planet.

It’s position among the stars of Gemini was also significant. Professor Lowell, proficient in celestial mechanics, had initially calculated the locus of Planet X to be in Libra, but upon later revisions, he revised this, first to eastern Taurus before finally settling on Gemini. Lowell had at last been vindicated, albeit posthumously. Dr. Slipher was in no hurry to announce the news just yet though. He was far too cautious for that. Thinking ahead, he ordered Tombaugh to take another set of exposures of the region near Delta Geminorum with the 13 inch astrograph, while Lampland was to obtain more precise positional data on the object using the 42 inch reflector. The comparator was fitted with a higher power microscope in order to obtain more accurate data on the object’s kinematics in order to compute its orbit.  On the evening of Wednesday February 20, Slipher, Lampland and Tombaugh opened the dome of the great refractor and pointed it at the new object. What they saw disappointed them. It was dim (of the 15th magnitude) and was completely indistinguishable from the other stars in the field! If this was a new world, it was very small. Indeed, the uninspiring telescopic sight of the planet induced a degree of paranoia in Tombaugh. What if this wasn’t Planet X after all? Maybe if he searched some more he’d find a larger object, more befitting of the icy giant worlds discovered by Sir William Herschel, Urbain Le Verrier and John Couch Adams?

As the days passed by, some other scientists were notified for consultative purposes, including Vesto’s brother and fellow astronomer, Earl C. Slipher, and Harlow Shapley, the then Director of Harvard College Observatory, in strict confidence that it would, for now, go no further. One date seemed especially appropriate; March 13 1930. It was Percival Lowell’s birthday; the highly esteemed persona who had given birth to the dream. It was also the 149th anniversary of Herschel’s discovery of Uranus. In the meantime, they would get their heads down and find out as much as possible about this small new world at the edge of the known Solar System.

Tombaugh went to work making a better estimate of the object’s magnitude, which he revised to magnitude 15.25. To get a better fix on its orbit, the staff re-examined plates from 1929. If they could find an earlier position of Planet X, they reasoned, they would have a larger arc to work with and hence be able to pin down its orbit with greater accuracy. But time was seriously against them and the search did not yield anything. The faithful day had arrived. Shortly after midnight on March 13, Tombaugh, Slipher met in the secretary’s office at Lowell Observatory and despatched a telegram to Harlow Shapley, who in turn immediately informed the International Union’s Bureau in Copenhagen. In addition to these telegrams, the Observatory issued a circular entitled, “The Discovery of a Solar System Body Apparently Trans Neptunian.” The circular gave some background to the project, how it was spearheaded by Lowell in 1905, discovered by Tombaugh and was being followed up and photographed regularly by Lampland. In addition, the celestial coordinates of its position at discovery was issued.

By the evening of March 13, the newspapers got wind of the story, and with that, the usual hodgepodge of misinformation.  Some didn’t metion Tombaugh at all, while in other stories his named was lost amongst a dozen other characters associated with the search since 1905. Back home in Burdett, Kansas, journalists from the local newspaper came out to the Tombaugh farm to get some background information for a cover story. In the space of a few hours the name “Clyde Tombaugh” was on the lips of everyone in the State and in the days that followed, he became an international ‘wonder boy’. But the announcement was also accepted with quite a bit of cynicism, especially from the professional community. Some astronomers questioned whether it really was a planet or merely a slow moving asteroid or comet near its aphelion. Others complained that the Lowell astronomers could not yet definitively say whether it was a trans Neptunian world without issuing its orbital details; data they had not yet been amassed with any accuracy. All of this upwelled troubling thoughts in Tombaugh’s young mind; the thrill of discovery was now tainted with lingering doubts and feelings of inadequacy.

The staff at Lowell Observatory were wise not to issue the precise coordinates of Planet X, as everyone and their grandmother was trying to find it. By June 1930, two further plates were recovered featuring the object in March and April 1915 and an intriguing record emerged from astronomers based in Uccle Observatory, Belgium, who had allegedly recovered the same object on a photographic plate dated to January 27 1927. These data greatly assisted the celestial mechanicians to place Planet X’s orbit on a much sounder footing. This was no comet; it was a real planet.

The appellation “Planet X” of course, would not satisfy a curious public, so the matter of bestowing an official name on the planet grew in urgency. Percival Lowell’s widow, Constance, suggested the name “Zeus” but upon later reflection humbly (no, not really!) offered “Percival,” and then, in a somewhat egotistical vein, “Constance,” which infuriated Tombaugh. However, conservatism had the last word, and so in keeping with the tradition of the names given to the other planets in our Solar System, Planet X would have to be Romanised. Many suggestions were forwarded, including Minerva and Cronus, but it was the suggestion made by an 11 year old English girl, herself a keen student of classical mythology, Venetia Burney, who suggested “Pluto”; after the Roman god of the underworld. What’s more, as V.M. Slipher pointed out, Pluto’s lettering started with the initials of Percival Lowell’s name, which sated the desire of the senior staff at Lowell Observatory  to ‘canonize’ their founding father. The name resonated with the public too. So from May 1 1930 Planet X was now known as Pluto.

The discovery of Pluto suggested to astronomers that there may be other objects lurking in the shadows beyond Neptune’s orbit. Many astronomers begun such searches and it soon became incumbent upon the staff at Lowell Observatory to resume further searches. This Tombaugh did for much of that late Spring. During this time, many more visitors were making the pilgrimmage to Mars Hill and Clyde was asked to submit popularised articles to various ‘highbrow’ periodicals, which he carried out with great diligence and enthusiasm. He even got a personal visit from Constance Lowell, immaculately turned out all in funeral black, like some grotesque parody of Queen Victoria of Great Britain. Constance was by all accounts, a snooty and overpowering character who never really accepted Tombaugh as the discoverer of “her husband’s planet.”

With the advent of the rainy season in July 1930, Clyde was granted three weeks leave to go home and see his family in Kansas and to finally meet his baby sister for the first time. It was a joyous reunion for the young man who made it to the big time, and like Cincinnatus of old, laying down the bloodied cloak of a soldier to embrace the ploughshare, so too did Tombaugh relish the prospect of returning to the wheat and the threshing floor on his family’s farmstead. It was a breath of fresh air for the famous farmer turned astronomer. He also got to use his dearly missed 9 inch reflector for bouts of recreational astronomy under summer skies.

After his well earned vacation, Tombaugh returned to Lowell Observatory to carry on the search for new trans Neptunian objects. If anything, the next few years were even more taxing than before, as the search became more extensive, covering much larger areas of sky.  But although his work brought up many false positive results, he did have the pleasure of clarifying the nature of one object, a globular cluster, NGC 5694, in Hydra, first identified by Sir William Herschel in May 1784 as a fuzzy star. It was also a time where Tombaugh ‘evangelised’ his formally trained colleagues, constructing a number of reflecting telescopes for casual sweeping. Indeed, Clyde is rumoured to have constructed the first ultrarich field reflector in the United States; a 5 inch f/4 instrument which enthralled Lampland, Slipher and others. As a personal telescope though, Tombaugh was a bit more discriminating. A relative aperture of 5 was just about acceptable to him on account of the amount of coma it showed at the edge of the field. But f/6 or slower was far superior in his opinion. Indeed, during these years, he would argue that a long focus Cassegrain reflector would knock the socks off the 24 inch refractor and he was even able to definitively offer a reason why the 42 inch reflector erected west of the great refractor gave less good visual results on most occasions. The mounting, he discovered, was shoddy, and because it was erected just below ground level it suffered far more from thermals. Still, his recommendations fell on deaf ears. The 24 inch was elevated to the status of a ‘holy relic’ and no amount of reasoned argument was enough to sway Lowell’s learned disciples.

Indeed, Tombaugh conducted his own set of experiments on the great refractor on Lowell’s favourite target, Mars, and his conclusions were very revealing. At the powers Lowell used (typically 400x) with a stopped down lens, Tombaugh was absolutely certain that he saw the canals as Lowell reported them. But he felt that Lowell was quite unscientific in his choice of magnification. Specifically, when the power was increased some more, the straight canals lost their linearity. Lowell was obsessed with canals though. He desperately wanted them to exist, and even saw them on Venus, Mercury as well as on the Galilean satellites of Jupiter!

Tombaugh also conceded that the dramatic seasonal changes on Mars as seen through the great refractor did often look like the march of green vegetation, with some canals appearing and disappearing from one apparition to the next. This was a common perception though, as astronomers were completely open to the idea that some form of plant life could eke out a living on the Red Planet right up until the advent of the Space Age.

Despite Tombaugh’s international fame, it was not accompanied by wealth. Nor did he actively seek it. The University of Kansas offered Tombaugh a four year Edward Emory Slosson Scholarship in 1931, the first of its kind, but he chose to postpone his University studies for a year in order to complete the ambitious survey he was assigned to. It was while studying for his Bachelors degree in astronomy (graduating in 1936) that he met his future wife, Patricia Edson, who also graduated with an honours degree in the Liberal Arts. ‘Patsy,’ seven years his younger, married Clyde in June 1934 and accompanied her husband back to his accommodation at Lowell Observatory. Tombaugh went on to earn a Masters degree in astronomy at the same University in 1938. His employers at Lowell Observatory were only too happy to see him complete his formal education, as they felt that would make him a more ‘rounded’ scientist.

Except for a year long hiatus to complete his Master’s degree in 1938, Tombaugh resumed his photographic patrol of the sky with the 13 inch astrograph atop Mars Hill, Arizona, but was fully cognizant of the rapid developments the better equipped observatories were making, especially with the giant 60 and 100 inch reflecting telescopes on Mount Wilson in California. Tombaugh began to think of other ways to use the huge quantities of image data captured by his photographic surveys. It occurred to him that the same data could be used to uncover new variable stars, asteroids and comets and sure enough it did. In addition though, it brought dividends concerning the distribution of the spiral nebulae, the ‘Island Universes’ beyond the confines of the Milky Way. Specifically, Tombaugh uncovered a striking increase in the number of galaxies in the Great Square of Pegasus and extending eastward as far as Perseus. V.M. Slipher was very excited about this discovery and encouraged Clyde to write up a paper on his findings, which he presented at the Astronomical Society of the Pacific, which convened in Denver, Colorado, in June of 1937. Tombaugh uncovered evidence that galaxies too are arranged into higher order structures like clusters and super clusters, stoking a brand new line of galactic astronomy that continues apace to this day. But the rise of Nazi Germany in Europe and the jostling for power in the Pacific Basin was about to trigger a World War that would change everyone’s priorities.

The outbreak of World War II brought sweeping changes to the lives of millions of people across the globe. And Clyde’s circumstances were no different, especially after the events of Pearl Harbor on December 7 1941. In February 1943, while still officially working at the Lowell Observatory, he was invited to teach a physics class at Arizona State Teacher’s College at Flagstaff, a post which he accepted but only briefly held, as the U.S. Navy headhunted him to teach navigation to a new generation of mariners at Northern Arizona University. Although he felt unqualified to take the post, the navy commander in correspondence with Tombaugh reassured him that he was, especially since he had by now gained the trigonometrical skills in his astronomy training to grapple with the course content. He felt it his duty to accept the new job, postponing, for now at least, his work with Lowell Observatory. Then, in 1944, Tombaugh was approached by the University of California at Los Angeles (UCLA), which offered him a decent wage for teaching two semesters of astronomy classes to undergraduates. He accepted that post and enjoyed his time in California.

By this time however, tensions were being strained with his relationship with the staff at Lowell Observatory, who felt that his skills were now dispensable. Slipher was also showing outward signs of jealousy toward Tombaugh, who, in his opinion, had stolen the show with his sole claim on Pluto. He was formally dismissed from the institution in 1945.  It was hard to know which way to go for the Tombaughs in the immediate aftermath of the War but it was Patsy’s brother, James Edson, who provided the way forward. Having just secured a good job at White Sands Missile Range, New Mexico, where the U.S. military were developing their space age defence technologies. As part of their ambitious program, they needed someone to operate a new long focal length telescope to image missiles in flight. Tombaugh’s expertise in practical and theoretical optics made him just the man for the job. The money wasn’t bad either, all the more important to support their two new arrivals, Anette and Alden.  Clyde was to work and live at the base and from October 1946, Patsy and her two kids stayed at rented accommodation in the nearby town of Las Crusces. From the outset, Clyde’s training as a telescopist brought dividends to his new employers, by greatly improving the tracking capability of V2 rockets. For example, he soon discovered that one of the major reasons why the missiles could not be tracked over long distances was because of the times at which they were launched; usually 11 am. Tombaugh pointed out that there was so much turbulence in the air at this time that it would greatly impede optical telemetry efforts. He suggested instead that they change the time of launch of the V2 missiles to either the early morning or early evening when thermals were much less of an issue. He also suggested that instead of using the traditional achromatic telescopes for tracking, they ought to build a large aperture reflecting telescope (16 inch f/6), which offered better optics (owing to the lack of chromatic aberration) at much reduced expense.

His almost overnight success at White Sands military base gave him a level of security he never enjoyed in the stuffy intellectual climate he experienced toward the end of his days at Lowell Observatory. His comrades at the base elevated him to the status of a hero and he was constantly in demand to recount his story of how he discovered the furthest planet known in the Solar System. And a good, regular salary allowed the Tombaugh’s to purchase their first house at 636 South Almeda, Las Cruces, albeit in a rather dilapidated state (a new roof being chief among the repairs needed). This was to be their home for the next two decades. By 1950, Tombaugh had fulfilled all the major technical tasks his employers had asked of him and he was thereafter able to return to the hobby which had launched his career. He wrote his father back in Kansas, requesting him to send on his old 9 inch reflector so that he resume his amateur work. It was a round this time also that he started thinking about the planets again, particularly Mars, which had captivated him ever since his youth. Accordingly, he wrote up and published a couple of interesting research papers predicting the presence of impact craters on the surface of Mars, owing to its very thin atmosphere and its greater proximity to the asteroid belt. This work presaged the findings of Mariner IV, which in 1965 showed conclusively that the Red Planet was peppered with craters of all shapes and sizes, making it more like the Moon than anything else.

It was in 1953 that Tombaugh became personally involved in the search for Near Earth Objects and/or small, natural satellites, to assist the government in establishing how safe it was to launch spacecraft into near Earth space. In essence, the nature of these searches were the same as those Tombaugh carried out in his earlier planet searching days at Lowell Observatory, although since the objects were so much closer to our planet, they would move much larger distances on photographic plates per unit time. Ironically, one of the best instruments for doing this kind of work was the 13 inch Lawrence Lowell telescope atop Mars Hill. Tombaugh found himself commuting between Flagstaff and White Sands, only this time he was fully funded by the U.S. military with assistants under his command. The cash starved adminstrators on Mars Hill were only too happy to acquiesce. While there was some cause to keep aspects of the project secret, Tombaugh publicly announced at a meteor conference held at Los Angeles in 1957 that the four year long search had been unsuccessful.

The 1950s represented a time of unprecedented scientific progress. Literally anything was possible. Cures for cancer were just around the corner, and new drugs had conquered nearly all diseases that had plagued humankind for millennia. Now Man was setting his sights on the heavens and the discoveries that might lie in our future. Although Tombaugh never studied the subject, he blindly believed in Darwinian evolution and thus fully expected there to be intelligent life elsewhere in the Universe. Curiously, this happened around the same time he down played his traditional Christian beliefs and embraced the all singing, all dancing, Unitarian Universalist (read anything goes) church. Intriguingly, this dovetailed with his growing interest in Unidentified Flying Objects (UFOs). Indeed, Tombaugh not only believed that UFOs were a manifestation of extraterrestrial intelligence, he actually reported seeing ‘six to eight’ such objects on August 20 1949 near his home at Las Cruces, New Mexico. What is more, it is also known that he offered to spearhead a new project for the military to capture these objects with the telemetric technology available to him at White Sands.

What an extraordinary convergence of ideologies! For the record, the consensus opinion among secular scientists who have studied the phenomenon over several decades concluded that UFOs have a strong demonic dimension.

From 1955 until his retirement in 1973, Tombaugh joined the academic staff at New Mexico State University, where he took up a research interest close to his heart; the visual and photographic monitoring of planets which came into effect around 1958. Calling it the Planetary Patrol and Study Project, Tombaugh and his colleague Bradford Smith (who would later become an imaging scientist with the Mariner and Voyager missions), set up a fine 12 inch f/6.7 Newtonian just off campus. Funded by small grants from the National Science Foundation, it began taking images of the major planets across a broad range of wavelengths from the ultraviolet right the way through to the infrared. The instrument was later moved to an even better site in the nearby Tortugas Mountains. In addition to these multispectral photographic studies, regular visual drawings were made of Jupiter, Saturn, Mars and Venus. Collectively, the data was used to assist NASA’s ambitious Mariner and (later) Pioneer spacecraft program. Optically, the 12 inch was reputed to be very fine indeed. To get an idea of how good it was, a visiting astronomer from Lowell Observatory had the pleasure of using it for a short spell and he declared that its images were sharper and clearer than the best images rendered with the old 24 inch Clark refractor on Mars Hill.

The Mariner missions to the planets were received with mixed blessings by Tombaugh. On the one hand, he was delighted that the Mariner IV spacecraft had beamed back solid evidence that the Red Planet was littered with craters, but was very disappointed that no evidence for Martian vegetation was forthcoming from the same mission. Because of his misplaced faith in evolution, Tombaugh was sure that the ‘waves of darkening’ he observed through his telescopes over the years were the manifestation of plant life and never really gave up hope that one day they would discover life there.

As well as his beloved 9 inch reflector, Tombaugh dusted down an old project he had begun in the 1930s and early 1940s involving a substantially larger personal telescope; a 16 inch f/10 Newtonian. Indeed, the mirror had been ground by 1944 but because of work commitments, he had to foreswear until 1960, when he finally completed the telescope. By this time the Tombaughs had moved into a larger and more opulent home setting at the southeastern apex of Las Crusces. He donated this instrument, which had an Honest John Booster as a tube, together with a very heavy equatorial mount to the newly founded Las Crusces Astronomical Society.

All who assessed the quality of the work conducted with the 12 inch for the Planetary Patrol Project, agreed that it was of the highest quality and of great importance to the developing space program. Indeed, Tombaugh was able to persuade NASA to provide funding for not one, but two 24 inch reflectors; one to be dedicated to planetary studies and the other to extend stellar and extragalactic research. The archives at NMSU have preserved about a million photographs of which more than half were taken of Jupiter. By 1961, the Planetary Patrol Project and Study Group consisted of a team of five scientists and it was about this time that NMSU officials approached Tombaugh to set up a brand new department within the University system. Although he was reluctant to do so, Tombaugh eventually amalgamated the originally small Department of Geography & Geology into a new and substantially larger Department of Earth Sciences and Astronomy.

Tombaugh’s retirement years were long and productive, and not surprisingly, he was approached by all and sundry to write his memoirs of his extraordinary career, as well as his philosophy of life. Interestingly, he vehemently denied, despite the battery of hard physical evidence in support of it,  that the Universe had a beginning, as that would give too much credence to the Biblical narrative, which clearly (and uniquely) states in its opening line the prophetic words:

In the beginning God created the Heaven and the earth.

Genesis 1:1 (from Tombaugh’s copy of the Authorized King James Version)

Indeed, for a man who supposedly eschewed ‘the illogical,’ his denial of Big Bang Cosmology was somewhat hypocritical.

And although his hands were associated with many an amateur telescope, he enjoyed deep sky observing with a 10 inch f/5 Newtonian. His iconic 9 inch reflector was donated to the Smithsonian Institution as part of the display dedicated to the “Nation’s Attic.” He collaborated with Sir Patrick Moore on a new book chronicling his discovery of Pluto; Out of Darkness, The Planet Pluto; which was published in 1980, the highlights of which were serialised in a series of Sky & Telescope articles appearing about the same time. Much of his retirement days were also spent travelling as guest speaker at a number of amateur gatherings the length and breadth of the country. Indeed, as one biographer noted, he was busier during these years than he had ever been while in full time employment. Many honours were bestowed upon him, and none undeservedly, including a kindergarten school at Las Crusces, an entire Observatory at NMSU and at the University of Kansas, as well as the Jackson–Gwilt Medal of the Royal Astronomical Society.

But his career was tinged with a great deal of personal sadness, as his most famous discovery was progressively demoted in importance owing to the discovery of several other trans Neptunian objects, most notable of which was 1992 QB1. The reality was that Tombaugh had inadvertently opened a veritable Pandora’s Box of new objects residing in the Solar System’s Kuiper Belt. And, to add insult to injury, there was growing talk that the discovery of more and more Kuiper Belt Objects (KBOs) would almost certainly mean that Pluto would have to be downgraded to the status of the first discovered member of a new group of ‘dwarf planets.’

The dwarf planet 134340 Pluto, as imaged by the New Horizons spacecraft on July 14 2015. Image credit: Wiki Commons.

Tombaugh passed away quietly in his wheelchair on Friday January 17th 1997, survived by his wife and two children. Less than ten years later, the 26th Assembly of the International Astronomical Union voted, predictably, to reclassify Pluto as a dwarf planet (134340 Pluto), and so the Solar System went back to having eight members. After his cremation, a small part of his ashes (30g) were placed inside a vial that was carried by NASA’s New Horizon Spacecraft, which visited Pluto and its entourage of moons in July 2015, beaming back a wealth of high resolution images of this distant ice world on the edge of the Solar System. One of its major features, a vast ice field, was also named in his honour; Tombaugh Regio.

Clyde William Tombaugh (1906 –1997); a life in science.

References & Further Reading

Levy, D.H. Clyde Tombaugh, Discover of Planet Pluto, Sky Publishing Corp, 2006.

Tombaugh, C. & Moore, P., Into the Darkness, The Planet Pluto, Harrisburg, Pennsylvania. Stackpole, 1980.

Sheehan, W. The Immortal Fire Within, The Life and Work of Edward Emerson Barnard, Cambridge University Press, 1995.

Ashbrook, J., The Astronomical Scrapbook, Sky Publishing, 1984.

Ross, H. Samples, K & Clark, M. Lights in the Sky and Little Green Men, NavPress Publishing Group, 2002.

Steiger, B., Project Bluebook, Ballatine Books, 1976.

Menzel, D. & Boyd, L.G.,The World of Flying Saucers: A scientific examination of a major myth of the space age, Doubleday, 1963.

Biographical Link: https://carlkop.home.xs4all.nl/clyde.html


Dr. Neil English is author of several books on amateur telescopic astronomy and is currently writing a new work entitled: Tales from the Golden Age of Astronomy, published in the spring of 2018.


De Fideli.

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