The Effects of the Reflecting Telescope on the World
In 1668 Isaac Newton constructed the first practical reflecting telescope. But mirrors were more difficult to fabricate than lenses, so the astronomical action stayed with refractive telescopes --- those built from lenses --- for almost 100 years. Then, for the next 120 years or so, refractive and reflective telescopes were both at the forefront of astronomy.
But as refractive telescopes get bigger, the lenses get thicker and heavier, and the lenses also spread colors, blurring the images. The 40" diameter refractor installed in 1897 at Yerkes Observatory is the largest astronomical refracting telescope. The problems with refractive telescopes were too tough to handle for larger telescopes, so all significant astronomical telescopes built since then have been reflective telescopes. The list of their significant discoveries could fill a book, but some highlights can give an idea.
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.
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
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
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
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 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.
- CalTech: Telescopes in History
- University of Chicago: Yerkes Observatory
- Sloan Digital Sky Survey: The Hubble Diagram
- Keck Observatory: Discovery Triples Number of Stars in Universe
- Keck Observatory: Keck Observatory Discovers First Goldilocks Exoplanet
- PopSci.com: Hubble's Ten Most Significant Discoveries; Stuart Fox; May 26, 2009
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