AsTRONOMY UNDERSTANDING THE UNIVERSE Ptolemy's notion that the Sun revolves around Earth was invalid instead he con cluded that Earth and the other planets actually orbit around the Sun But there was no way to prove Copernicus idea until the invention of the telescope This revolutionary new piece of technology allowed Italian astronomer Galileo Galilei in the early 1600s to carefully record the move ment of different heavenly bodies including four moons which he observed revolving around Jupiter Galileo's findings paved the way for the confirmation of Copernicus theory Over time telescopes have been get ting larger and more powerful Now there are even telescopes in space NASA s Kepler space telescope recently revealed a rocky planet named Kepler 1ob that astronomers believe to be the smallest planet ever discov ered outside our solar system In the 20th century scientists deepened their understanding not only of astronomy but also cosmology the study of the universe and its laws Along with technology scien tists use mathematics and physics to make discoveries Albert Einstein revolutionized cosmology in 1905 with his special theory of relativity which stated that space and time
INTRODUCTION could be seen as parts of a deeper structure space time and that mass and energy are really the same thing Scientists later devel oped the big bang theory According to this theory the universe started some 13 billion years ago with a sudden expansion of mat ter and antimatter Many scientific tests have confirmed the validity of this theory In this book you will learn about impor tant advances that astronomers have made through time But you will also learn that astronomy is one of the few sciences in which amateurs can play a significant role You do not need your own Kepler telescope or a Ph D in physics to make a significant con tribution With the proper tools including knowledge and a sharp eye even an amateur can make an important discovery In 1995 two amateur astronomers Alan Hale and Thomas Bopp working independently of each other spotted a comet beyond the orbit of Jupiter Comet Hale Bopp as it came to be known reached perihelion the closest distance to the Sun on April 1 1997 without ever coming very close to Earth It was however spec tacularly visible to the naked eye and became perhaps the most widely witnessed comet of the 20th
THE VISIBLE SKY ince the beginnings of humankind peo ple have gazed at the heavens Before the dawn of history someone noticed that certain celestial bodies moved in orderly and predictable paths and astronomy an ancient science was born Yet some of sci ence s newest discoveries have been made in this same field which includes the study of all matter outside Earth s atmosphere From simple observations of the motions of the Sun and the stars as they pass across the sky to advanced theories of the exotic states of matter in collapsed stars astronomy has spanned the ages For centuries astronomers concentrated on learning about the motions of heavenly bodies They saw the Sun rise in the east and set in the west In the night sky they saw tiny points of light Most of these lights the stars seemed to stay in the same place in relation to one another as if they were all fastened to a huge black globe surround ing Earth Other lights however seemed to travel going from group to group of sta tionary stars They named these moving Io
THE VISIBLE SKY New stars are forming from the hot gas and dust of the Orion nebula a major stellar nursery only some 1 500 light years from Earth Our sun probably formed in a similar environment More than 500 separate images were combined to create this mosaic NASA ESA M Robberto Space Telescope Science Institute ESA and the Hubble Space Telescope Orion Treasury Project Team II
