How I Killed Pluto and Why It Had It Coming Read Online Free PDF Page A

sky. The earth
is
a planet. What seems so obvious and ingrained in us today must have been profoundly disorienting. I’ve tried to put myself in the frame of mind of the time and tried to understand how shocking it would have been, but I’ve never come close. It is as hard for me to image an Earth-centered universe as it would have been for them to imagine anything else. Everybody thought they knew what a planet was, and suddenly, one appeared beneath their feet.
    And what of the moon? At least Earth was special in that, of all the planets, it alone had another body going around it. But when Galileo first pointed his crude telescope at the sky in 1609, he discovered that Jupiter, too, had objects going around it (now called the Galilean satellites). Any reasonable pair of binoculars will show you the same thing. Find Jupiter, point the binoculars up (lean against a wall to steady your shaky hands), and you’ll see the disk of Jupiter and maybe even some bands of wispy clouds on the disk. Perhaps you’ll also see four tiny white dots strung ina line all to one side of Jupiter. The next night look again, and one of the tiny dots might be missing—hidden behind Jupiter—and one might have moved to the other side. The next night they will change again. The little moons are wandering around the wanderer. One of them even has volcanoes. I could tell you a lot about those volcanoes.
    Even with Galileo’s primitive telescope, he could tell that there were stars in the sky that were too faint for the eye to see. Did he or anyone else think about whether or not there were planets in the sky that were too faint for the eye to see? No one appears to have written about the possibility. Perhaps no one even thought about it. Though the planets had been rearranged and now were secondary to the sun, and the earth had been demoted from the center of the universe to the same status as the other planets, perhaps the possibility of additional planets circling the sun so faintly that we wouldn’t know about them was simply beyond comprehension. Why would such invisible things have been put there in the first place?
    It took almost two more centuries to stumble upon the answer. In 1781 the British astronomer William Herschel was charting faint stars that could be seen only through his new advanced telescope. He came to one star that looked bigger than the stars around it, which was strange, since all of the stars look simply like points of light and none appears bigger than another. When he looked again the next night, the unusual star had moved. He had found a new wanderer. But since it couldn’t be a planet (obviously, since all of the planets were known, right?), what was it? Herschel assumed it was a comet near the earth. Within only a few months, however, he realized that the new object was in a circular orbit well beyond Saturn, where nothing else had ever been seen before. It was no comet, it was a planet. Herschel measured the size of the greenish disk he had foundand realized that this new body had to be big—not quite as big as Jupiter or Saturn, but much bigger than any of the other planets in the solar system. The word
planet
quite naturally expanded to include this new body distantly circling the sun: the seventh planet had been found. Jupiter, the largest planet, was named after the king of the gods. Saturn, originally the most distant known planet, was named after the father of Jupiter. The new wanderer, even more distant than Saturn and unrecognized throughout history until the moment Herschel distinguished it from the stars around it, was—eventually, after sixty years of debate—named Uranus, for the most ancient of all the gods. The element uranium, discovered only seven years later, was named in honor of the new planet.
    Everybody had known there were only six planets until the moment the seventh was found, but once the prejudice against the idea of new planets was overcome, the idea that there could be other unseen