Read Online Death by Black Hole: And Other Cosmic Quandaries by Neil deGrasse Tyson - Free Book Online Page B
Authors: Neil deGrasse Tyson
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Earth, except along the equator, the plane still turns, but more and more slowly as you move from the Poles toward the equator. At the equator the plane of the pendulum does not move at all. Not only does this experiment demonstrate that it’s Earth, not the Sun, that moves, but with the help of a little trigonometry you can also turn the question around and use the time needed for one rotation of the pendulum’s plane to determine your geographic latitude on our planet.
The first person to do this was Jean-Bernard-Léon Foucault, a French physicist who surely conducted the last of the truly cheap laboratory experiments. In 1851 he invited his colleagues to “come and see the Earth turn” at the Pantheon in Paris. Today a Foucault pendulum sways in practically every science and technology museum in the world.
Given all that one can learn from a simple stick in the ground, what are we to make of the world’s famous prehistoric observatories? From Europe and Asia to Africa and Latin America, a survey of ancient cultures turns up countless stone monuments that served as low-tech astronomy centers, although it’s likely they also doubled as places of worship or embodied other deeply cultural meanings.
On the morning of the summer solstice at Stonehenge, for instance, several of the stones in its concentric circles align precisely with sunrise. Certain other stones align with the extreme rising and setting points of the Moon. Begun in about 3100 B.C . and altered during the next two millennia, Stonehenge incorporates outsize monoliths quarried far from its site on Salisbury Plain in southern England. Eighty or so bluestone pillars, each weighing several tons, came from the Preseli Mountains, roughly 240 miles away. The so-called sarsen stones, each weighing as much as 50 tons, came from Marlborough Downs, 20 miles away.
Much has been written about the significance of Stonehenge. Historians and casual observers alike are impressed by the astronomical knowledge of these ancient people, as well as by their ability to transport such obdurate materials such long distances. Some fantasy-prone observers are so impressed that they even credit extraterrestrial intervention at the time of construction.
Why the ancient civilizations who built the place did not use the easier, nearby rocks remains a mystery. But the skills and knowledge on display at Stonehenge are not. The major phases of construction took a total of a few hundred years. Perhaps the preplanning took another hundred or so. You can build anything in half a millennium—I don’t care how far you choose to drag your bricks. Furthermore, the astronomy embodied in Stonehenge is not fundamentally deeper than what can be discovered with a stick in the ground.
Perhaps these ancient observatories perennially impress modern people because modern people have no idea how the Sun, Moon, or stars move. We are too busy watching evening television to care what’s going on in the sky. To us, a simple rock alignment based on cosmic patterns looks like an Einsteinian feat. But a truly mysterious civilization would be one that made no cultural or architectural reference to the sky at all.
SECTION 2
THE KNOWLEDGE OF NATURE
THE CHALLENGES OF DISCOVERING THE CONTENTS OF THE COSMOS
SIX
JOURNEY FROM THE CENTER OF THE SUN
D uring our everyday lives we don’t often stop to think about the journey of a ray of light from the core of the Sun, where it’s made, all the way to Earth’s surface, where it might slam into somebody’s buttocks on a sandy beach. The easy part is the ray’s 500-second speed-of-light jaunt from the Sun to Earth, through the void of interplanetary space. The hard part is the light’s million-year adventure to get from the Sun’s center to its surface.
In the cores of stars, beginning at about 10-million degrees Kelvin, but for the Sun, at 15-million degrees, hydrogen nuclei, long denuded of their lone electron, reach high enough speeds to
The first person to do this was Jean-Bernard-Léon Foucault, a French physicist who surely conducted the last of the truly cheap laboratory experiments. In 1851 he invited his colleagues to “come and see the Earth turn” at the Pantheon in Paris. Today a Foucault pendulum sways in practically every science and technology museum in the world.
Given all that one can learn from a simple stick in the ground, what are we to make of the world’s famous prehistoric observatories? From Europe and Asia to Africa and Latin America, a survey of ancient cultures turns up countless stone monuments that served as low-tech astronomy centers, although it’s likely they also doubled as places of worship or embodied other deeply cultural meanings.
On the morning of the summer solstice at Stonehenge, for instance, several of the stones in its concentric circles align precisely with sunrise. Certain other stones align with the extreme rising and setting points of the Moon. Begun in about 3100 B.C . and altered during the next two millennia, Stonehenge incorporates outsize monoliths quarried far from its site on Salisbury Plain in southern England. Eighty or so bluestone pillars, each weighing several tons, came from the Preseli Mountains, roughly 240 miles away. The so-called sarsen stones, each weighing as much as 50 tons, came from Marlborough Downs, 20 miles away.
Much has been written about the significance of Stonehenge. Historians and casual observers alike are impressed by the astronomical knowledge of these ancient people, as well as by their ability to transport such obdurate materials such long distances. Some fantasy-prone observers are so impressed that they even credit extraterrestrial intervention at the time of construction.
Why the ancient civilizations who built the place did not use the easier, nearby rocks remains a mystery. But the skills and knowledge on display at Stonehenge are not. The major phases of construction took a total of a few hundred years. Perhaps the preplanning took another hundred or so. You can build anything in half a millennium—I don’t care how far you choose to drag your bricks. Furthermore, the astronomy embodied in Stonehenge is not fundamentally deeper than what can be discovered with a stick in the ground.
Perhaps these ancient observatories perennially impress modern people because modern people have no idea how the Sun, Moon, or stars move. We are too busy watching evening television to care what’s going on in the sky. To us, a simple rock alignment based on cosmic patterns looks like an Einsteinian feat. But a truly mysterious civilization would be one that made no cultural or architectural reference to the sky at all.
SECTION 2
THE KNOWLEDGE OF NATURE
THE CHALLENGES OF DISCOVERING THE CONTENTS OF THE COSMOS
SIX
JOURNEY FROM THE CENTER OF THE SUN
D uring our everyday lives we don’t often stop to think about the journey of a ray of light from the core of the Sun, where it’s made, all the way to Earth’s surface, where it might slam into somebody’s buttocks on a sandy beach. The easy part is the ray’s 500-second speed-of-light jaunt from the Sun to Earth, through the void of interplanetary space. The hard part is the light’s million-year adventure to get from the Sun’s center to its surface.
In the cores of stars, beginning at about 10-million degrees Kelvin, but for the Sun, at 15-million degrees, hydrogen nuclei, long denuded of their lone electron, reach high enough speeds to
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