Since the dawn of human race, the night sky has been the object of much study and speculation. Persons from all walks of life have tried to explain the wonders that appear night after night in the sky.
What are the stars? How big is the universe? Where do we fit in? People have been asking these questions since earliest times, but the answers have been slow in coming.
The earliest people thought, naturally enough, that the universe was only what they saw: a sky dome over flat earth. Beyond that they simply made up stories.
The Egyptians saw the universe as a room, with the sky as a ceiling and earth as the floor. Egypt, of course, was in the center. The stars hung from the sky-ceiling like lamps, and the sun god Ra sailed around the sky once a day in a boat.
The ancient Babylonians believed the world floated on an immense ocean, while the gods lived on top of the sky dome. The sun came in through a door in the sky every morning and left through another door every evening.
Their myths were not based on any evidence, they were simple made up.
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GREECE AND THE BIRTH OF SCIENCE
About 2,500 years ago, in the land of Greece, a new way of thinking began to take root. In the broadest terms, it was the idea that the world is knowable- that the universe acts in predictable ways according to natural laws.
The Greek philosophers developed and refined geometry and much of mathematics, and they were amazed to discover the hidden laws that numbers obey. They applied their mathematics to the problem, and some came to believe that the celestial bodies are carried around the sky on invisible, hollow spheres, with earth at the center. This might not seem much improvement to the problem, but there was a big difference. The Greek universe was not run by the whims of irrational gods; it was orderly like a piece of machinery. Its motions could be studied and predicted.
The first person to accurately measure the size of earth was a scholar named Eratosthenes. Other philosophers realized earth is not motionless but rotates, or turns on its axis, once a day; that is why the sun, moon, and stars appear to rise and set. Human thought had gone from a flat earth and dome sky to the correct picture of our spinning planet flying through space- and all about 1,900 years before the invention of the telescope.
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THE COPERNICAN REVOLUTION
Nicholas Copernicus lived during the early 1500s. He spent much of his life trying to find a more philosophically and aesthetically satisfactory way than Greek theories to account for the motions of the planets. He succeeded by assuming that the planets, including earth, travel around the sun. Copernicus was a timid, reclusive man. He did not publish his theory shortly before his death. His theories were much debated.
A lively participant in those debates was Galileo Galilei, an outspoken and popular teacher of mathematics in Italy. In 1609, Galileo first looked at the sky with his newly invented telescope. With it he saw that moon has mountains and plains like those on earth. He discovered four tiny moons orbiting the planet Jupiter. He discovered that the planet Venus shows phases like those of the moon, which he saw as evidence that Venus circles the sun.
Tycho Brahe, a Danish nobleman, spent many years observing the positions of planets and measuring planetary positions in relation to earth and the sun. These measurements were far more accurate than any that had been recorded before. Using Brahes data, Johannes Kepler, a teacher in Germany greatly improved the Copernican system. He figured out that earth and planets move around the sun not in circles, but in ellipses. Kepler also discovered two mathematical principles that describe the speed of the planets in their orbit. With Keplers three laws of planetary motion, the shape and speed of the planetary orbits were at last understood.
Sir Isaac Newton (1642-1727), an English scientist, astronomer, and mathematician, showed through his theory of gravitation how the universe is held together. When Newton applied his mathematical formula of gravity to the planets, he found that it almost exactly accounted for the planets motion and the elliptical shapes of their orbits.
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THE GROWTH OF MODERN ASTRONOMY
With the evolution of telescopes, better and better telescopes were being turned to the sky, and hundreds of new techniques were invented to analyze the size, temperature, distance, motion and chemical composition of the stars. Double stars were discovered- pairs of stars orbiting around each other. Star clusters- nests of less than a dozen to many thousands of stars were revealed, as were nebulae, strange objects like great luminous clouds in space.
In recent decades, astronomy has expanded faster and faster. Astronomers now study not just the visible light of the universe, but its infrared and ultraviolet light, radio emissions, X-rays and gamma rays.
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