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Star Spangled Banter:
08/15/2007
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Discovering Pluto
Sir William Herschel was an organist who spent his days in church and his nights looking through his telescope, his sister Carolyn by his side. On the night of March 13, 1781, he observed a blue-green “star,” that he had never seen before. Its peculiar color attracted his attention. Unlike stars (which appear as points of light through the telescope) it appeared to be a small disc, like a planet. Mercury, Venus, Mars, Jupiter, and Saturn had been known since antiquity, but this discovery changed things. It was the first time in history another planet was discovered. Herschel sought to exploit his discovery by suggesting it be called Georgium Sidus (George’s Star), in honor of the King. His suggestion lost favor, and it was named Uranus, consistent with the tradition that planets bear names from Roman mythology. The story didn’t end there. Astronomers watched as Uranus moved in front of the more distant background stars, and calculated its orbit. But for some reason Uranus surged ahead of its calculated position for a few years, then inexplicably began to run behind its plotted position. Two astronomers, John Adams, in England, and Urbain Leverrier, in France, unknown to each other, both reasoned that the source of Uranus’s erratic behavior was an as-yet-unknown planet, lying outside of Uranus’s orbit. The gravity of this undiscovered planet tugged at the faster moving Uranus, speeding its motion around the sun, until at last Uranus passed it, after which time it tugged back, like a sore loser in the race, slowing the faster-moving inner planet. To prove their case, both men calculated where the suspected body was to be found. They both wrote detailed instructions to astronomers, telling them exactly where to point their telescopes. Adams completed his calculations a few months before Leverrier, and sent his data to the Cambridge Observatory in England. A series of communication breakdowns caused an excessive delay before Adams’ request received a proper response. On the other hand, Leverrier sent his calculations to the Royal Observatory in Berlin, where, on the night of September 23, 1846, the new planet (named Neptune) was found within 30 minutes. Although Adams actually won the race, Leverrier was given credit, and became a celebrity, while Adams was cast out of the limelight, a role not resented by the modest Adams. Leverrier, on the other hand, relished the spotlight and resented the attention given to Adams. The story doesn’t end there either. Neptune’s gravity was insufficient to account for all of the erratic behavior of Uranus. Astronomers then speculated that yet another planet lay outside of Neptune’s orbit. Thus began a search which captured the imagination of the public for more than eighty years. But Planet X, as it came to be called, must have been very faint, and many astronomers finally decided it did not exist, and lost interest. Not so the tabloids, nor Percival Lowell (of the wealthy and famous New England Lowell family). Armed with seemingly unlimited financial resources, he could pursue his cherished hobby, astronomy. He financed and built a major observatory, high in the clean mountain air near Flagstaff, Arizona, and dedicated most of its use to his twin obsessions (finding Planet X and the “canals” on Mars). Lowell used a tool called a blink microscope. This instrument compares two photographic plates of the same area of the sky, taken to the same scale on nights a few months apart. One plate is viewed with the right eye, rapidly alternating with the left eye view of the other. All objects that are the same in both plates appear stationary, but anything different – scratches, dust particles, blemishes in the emulsion, or anything that moved in the time between exposures – appears to jump in and out of the picture. This could include comets, asteroids, or, hopefully, Planet X! It was painstaking work, requiring infinite patience. Who knew how many specks might be missed if the viewer happened to be careless for just a moment? Lowell hired a compulsive and conscientious young Kansas farm boy named Clyde Tombaugh, who spent literally years at his job, comparing thousands of plates, each one of which was scanned in minute detail. During this quest Tombaugh also discovered comets, which had moved during the time between the plates, and previously unknown galaxies, which didn’t move, but which Tombaugh’s keen eyes recognized as unknown objects. Finally, Lowell’s quest paid off. Planet X leaped out of the photographs. The discovery of Planet X was announced on March 18, 1930, the 149th anniversary of the discovery of Uranus. Subsequently named Pluto, it is so far away that it has remained mysterious for the three quarters of a century since its discovery. Pluto’s orbit is the most eccentric of any of the planets, major or minor. Although none of the planets travel in perfectly circular orbits, the other planets travel along elliptical paths that are so nearly circular it is difficult to tell by looking. Pluto’s orbit, by contrast, is so elliptical that at one point it cuts into the orbit of Neptune, making Neptune the most distant planet for about 28 years of Pluto’s 238-year orbit. Since its discovery, Pluto has only completed about a third of a trip around the sun. Because of its extreme distance, it remains the only planet not visited by human (i.e., earth-based) spacecraft so far. Change is happening, however, because New Horizons, a spacecraft launched in January, 2006, will reach speeds of 47,000-56,000 mph (10 times faster than a speeding bullet). But Pluto is so far away it will still take nine years to reach. New Horizons is scheduled to fly past the dwarf planet in July, 2015! The name Pluto is commonly thought to be an homage to Percival Lowell, the first two letters being Lowell’s initials, while still maintaining the tradition of naming planets after Roman mythological gods. While some people dispute this story, it matters little. But I find it ironic that tiny Pluto seems much too small to influence the orbit of Uranus in any way. The other irony lies in the fact that recently some astronomers have claimed that the co-discoverers of Neptune were exceptionally lucky fellows, because had they used more accurate star maps, Adams and Leverrier would have pointed the astronomers some distance away from their advised positions. Whether or not true, at least it makes an intriguing story! And the final irony is that Pluto’s status has been officially downgraded to dwarf planet. © August, 2007, by Nathan B. Miron, Ph.D. Email: nathanmiron@kenwoodpress.com |
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