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The discovery of galaxies, quasars, and the "edge of the universe," is here recounted with clarity, simplicity, and stylistic elegance that has inspired...
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The discovery of galaxies, quasars, and the "edge of the universe," is here recounted with clarity, simplicity, and stylistic elegance that has inspired critics to hail Timothy Ferris as "the greatest science writer in the world."
Although the myriad things are many, their order is one.
-- Chuang Tzu
In the time it takes to read this sentence, the Earth will glide 200 miles in its orbit around the sun, the sun 3,000 miles in its orbit around the center of our galaxy, and 350,000 miles of additional space will have opened up between our galaxy and those of the Hydra cluster as the universe goes on expanding. The expansion of the universe is thought to have begun in a genesiac explosion (the "Big Bang") about 20 billion years ago. Astrophysicists and geologists estimate that the sun and its planets were born some 4.5 billion years ago, when the universe as we know it was something over two-thirds its present age. At a galactocentric velocity of 150 miles per second, the sun has wheeled around the center of the Milky Way Galaxy about twenty-five times since it was born. One percent of one orbit ago -- since which time the sun has moved across the face of our galaxy by less an increment than the second hand of a clock consumes in one second -- the species Homo sapiens evolved on the sun's third planet, Earth.
The Milky Way is one galaxy of perhaps two dozen that share membership in a cluster astronomers call the Local Group. Our nearest neighbors are two satellite galaxies, the Large and Small Magellanic Clouds, and a half dozen or so dwarfs. Two and a quarter million light-years away stands the Andromeda Galaxy, the dominant spiral of the group, an outsized replica of the Milky Way. The population of the Local Group is perhaps athousand billion stars.
Beyond, billions more galaxies recede in profusion in deepening space. The antique light from many of them was near completion of its long journey to our eyes when life on Earth had evolved as high as the sea urchin.
The universe contains at least as many galaxies as there are stars in the Milky Way.
Look up. A moonless late summer evening is a good time in the northern hemisphere. Face due east and you are looking away from the plane of our galaxy; out there, past a few thousand foreground stars, lies intergalactic space. Seven degrees above the star Beta Andromeda, you should be able to make out the soft glow of the Andromeda Galaxy. Turn and face due west, near the bright navigational star Arcturus. Here you are looking pretty well out of the whole Local Group. The inky sky between the foreground stars harbors clouds of remote galaxies.
From northeast to southwest arcs the Milky Way, our galaxy viewed from within. Sweep it slowly with binoculars -- the slower the better -- from Cassiopeia in the northeast. You will see meadowlands of stars cut with hints of glowing gas. One huge cloud of dark dust and gas reveals itself as a rift dividing the Milky Way from Cygnus to the southern horizon, like a rip in the sky. Approaching Sagittarius in the south, your field of view becomes heaped with stars. You are looking toward the heart of our galaxy.
Our knowledge of the depth of the sky is new. Our ancestors tended to envision the sky as a domed roof; Lucretius was not alone in thinking it so low that a war cry might fetch an echo off it. To have discovered that the sky is instead bottomless, that it represents nothing less than a view of the universe as seen from within a major spiral galaxy, was a feat more prodigious, in terms of scale, than if, say, a band of protozoa in a Philippine tidal basin were to have charted the Pacific Ocean. The scientific discoveries required to begin mapping the universe in three dimensions came about in a revelatory flurry in the twentieth century but involved research dating back centuries earlier.
When Galileo turned his telescope on the Milky Way, he found that it was composed of millions of stars. This was the first evidence that stars might be distributed not at random but as part of a system -- that, as we would say today, our sun and the stars we see in the sky are part of the disk of a spiral galaxy. Other galaxies were visible to Galileo, but they are so remote that their multitudes of stars blended together when viewed through his telescope. Consequently, Galileo was able to discern no fundamental difference between these "spiral nebulae" and the other nebulae that we today know are clouds of gas within our galaxy.
The eighteenth-century comet-hunter Charles Messier catalogued 103 nebulae, by way of warning other comet-seekers not to mistake them for legitimate prey. Many more were observed by the English astronomer William Herschel, who had a technologically premature passion for building big reflecting telescopes and who liked to boast, "I have looked farther into space than ever human being did before me." Herschel's son John continued his father's observations. Some of the nebulae looked like chalk-colored spiderweb tangled among the stars. Others were spiral in shape, resembling pinwheels. Throughout the nineteenth century, people were inclined to think that all the nebulae were gas or dust in our own stellar system. The one remarkable exception was the philosopher Immanuel Kant, who perceived, with little but reasoned intuition to guide him, that the delicate pinwheel nebulae might be galaxies.
In 1751 Kant, at that time a tutor in Königsberg, read a newspaper story about the speculative cosmologies of Thomas Wright, a pious English surveyor and amateur scientist who authored several theories of the cosmos. Some of Wright's models were mutually contradictory -- he proposed variously that the Milky Way was spherical or flat like a grindstone, composed of stars like the sun or just an illusion -- but the contradictions did not seem to bother him; he wrote his theories as kapellmeisters composed cantatas, as offerings to the greater glory of God. By...The Red Limit