William Herschel's Reflectors

• In 1770, professional musician and amateur astronomer William Herschel got frustrated with the telescopes that were available to him. He built himself a reflective telescope and soon after discovered the planet Uranus. His telescope was so good, the king of England made him the royal astronomer. When he became a professional astronomer, he built more reflective telescopes and made more discoveries, including the existence of binary stars, asteroids, and the discovery of infrared radiation.
  
  

Mount Wilson

• The Hooker Telescope, a 100-inch reflective telescope on Mount Wilson in California, was the largest telescope in the world from 1918 to 1948. Astronomer Edwin Hubble used its size to advantage, expanding the vision of the universe, then turning it inside out. His observations first proved that some of the fuzzy objects known as nebulae were actually other galaxies, much further away than other objects in the Milky Way. Then he combined his measurements with those of other astronomers to show that the universe is expanding.
  
  

The Hubble Space Telescope

• Measurements of distant galaxies allow precise measurement of the expansion of the universe.NASA/Getty Images News/Getty Images
  
  The Hubble Space Telescope only has a diameter of 2.4 meters, but because it is above the Earth's atmosphere, it can see wavelengths that don't make it to the surface of the Earth, and it doesn't suffer from distortion due to the atmosphere. Those advantages have enabled a variety of significant discoveries. For example, Hubble Space Telescope measurements accurately measured the rate at which the universe is expanding, the expansion that Edwin Hubble himself first proposed. The Hubble Space Telescope also first directly observed a planet in orbit of another star and black holes at the center of galaxies.
  
  

The Twin Telescopes at the Keck Observatory

• The Keck telescopes have made many observations both within and far outside the solar system.Getty Images/Getty Images News/Getty Images
  
  Nearly 14,000 feet above sea level, on Mauna Kea on the big island of Hawaii, the two 10-meter diameter reflective telescopes of the Keck Observatory search the heavens. The site has consistently good "seeing" conditions that allow the power of the large telescopes to be applied to projects requiring many observations. Among the multitude of discoveries made by these telescopes are observations that triple the estimate of the number of stars in the universe, and the evidence for the first Earth-like planet orbiting another star.
  
  

The Effects of Discoveries

• Scientific discovery is a source of knowledge and inspiration.Nick White/Photodisc/Getty Images
  
  These discoveries obviously are significant for triggering new theories or confirming old theories. For example, Edwin Hubble's discovery of the expansion of the universe provided specific new information about the evolution of the universe that eventually became part of the Big Bang theory, and the Hubble Space Telescope's discovery of black holes at the center of galaxies confirmed a theory about the source of energy at galactic centers. But the influence of such discoveries extends further, because the same physical rules that apply in the center of stars or the cold reaches of interstellar space also apply on Earth. The discoveries affect our understanding of the universe and our place in it.
  
  

More of the Iceberg

• The Spitzer Space Telescope is one of NASA's "Great Observatories."Getty Images/Getty Images News/Getty Images
  
  The composition of comets and their contribution to the creation of life on Earth, the stages of nuclear fusion at the center of stars, the presence of organic molecules necessary for life in interstellar gas clouds --- all these discoveries and hundreds more have been made by reflective telescopes. Reflective telescopes are all around the Earth and surround the Earth.