In the 19th and early 20th centuries, advances in mirror making, glass production, and lens grinding led to the construction of increasingly larger and larger telescopes, which in turn led to the building of permanent structures to hold these huge instruments. At first these observatories were built near big cities or where it was convenient for astronomers or their sponsors to visit them. But eventually people realized that where you put your telescope is almost as important as how big you can make it. Locations were chosen where the weather was best for observing, usually a place with a dry and somewhat warm climate. For the biggest observatories, mountain tops became the spot of choice, where the atmosphere was thinnest and least bothered by wind movement, making the view the clearest of all. At the Dorpat Observatory in Estonia, the Dorpat Equatorial, a 14-foot long telescope with a 9 1/2 inch lens, was for many years the largest refracting telescope in the world. It was called an equatorial because it was mounted in such a way that a clock device could move the telescope at the same rate as the Earth turned. Its movement went opposite the direction of the Earth, so an astronomer could lock onto a star or planet and examine it continuously without having to manually readjust the telescope's position. With the Dorpat, Wilhelm von Struve (1793-1864), the observatory director, did a complete survey of the northern hemisphere. He examined 120,000 stars. Two thousand of them were double stars, of which only 700 were previously known. Struve also directed the Pulkovo Observatory near Leningrad, where a refractor with a 15-inch wide lens was eventually installed. [Picture of Dorpat] William Parsons (1800-1867), third Earl of Rosse, constructed at his castle in Ireland what was eventually known as the Leviathan of Parsonstown, a 72-inch mirror attached to a 56-foot tube. He then built a supporting structure around it. The problem of providing a stable foundation was solved by placing the telescope on a platform of 27 cast-iron plates on a base of tree trunks. The whole assembly then rested on a ball and socket set into solid rock. When the telescope was mounted, fortress-like walls, fashioned to match the castle, were raised to shield the telescope on two sides. Lord Rosse employed most of the people in his district to make this grand achievement possible. [Picture of Rosse's Leviathan] In time, many other large telescopes were constructed all over the world, both reflectors and refractors, sporting wider and wider lenses, or mirrors with diameters of astounding size. Large 48-inch reflectors were mounted in Malta and Australia, for example, and in California, the Lick Observatory assembled a 36-inch refractor that helped Edward Barnard discover Amalthea, the first new moon of Jupiter found since Galileo's time. In Wisconsin, the Yerkes Observatory sponsored a 40-inch refractor, although the weather at Lake Geneva was at times so cold that they had to close the observatory dome for fear of damaging the instruments. One astronomer's nose froze to the telescope's metal side as he observed, and he tore off a chunk of skin while pulling away! [Yerkes 40-inch] George Ellery Hale (1868-1938), who helped raise money for the Yerkes 40-inch refractor, was also responsible for even larger telescopes in California: the 60-inch and 100-inch Mt. Wilson reflectors and the 200-inch Mt. Palomar reflector, called the Hale Telescope in his honor. The 100-inch Hooker telescope at Mount Wilson was the largest in the world for 30 years. Through it, spiral cloud-like nebulae were at last identified as being "island universes" or what we now call galaxies, just like our own Milky Way galaxy. [Mt. Wilson 100-inch. image 22, p. 328 Hoskin] The 200-inch Hale at Palomar, completed in 1949, then took over as the world's largest telescope. Weighing more than the Statue of Liberty, the huge instrument had the most perfect mirror ever polished. It revealed such wonders as the first quasars, star-like radio sources moving at incredible speeds at the edge of the visible universe. Astronomer Allan Sandage (1926- ), the first to spot a quasar and Palomar's most frequent and productive observer, showed the universe to be 10 times larger in size using evidence obtained with the Hale reflector. The telescope seemed to reveal the farthest parts of the universe. Strangely enough, when it was being built, some people feared it would allow mortals a view of heaven itself! Even in modern times, the awesome power of telescopes could still frighten people as it did in the 13th century. [200-inch Hale. image 23, p. 336 Hoskin] Built next to the 200-inch Hale the year before is the Big Schmidt, now called the Oschin Telescope, a 48-inch telescope-camera that is both a reflector and a refractor in one. This combination was invented by Bernhard Schmidt (1879-1935). Its advantage over the much larger Hale Telescope is its wider field of vision. Using the Schmidt, astronomers made a complete photographic map of the sky, something it would have taken the 200-inch Hale reflector millions of individual photographs to do. [Big Schmidt] After the observatories on Palomar were built, 30 years passed before the construction of larger ground-based telescopes, although a number of telescopes between the 100- to 200-inch range were constructed. In 1996, the two 10-meter (400-inch) Keck telescopes were completed atop Mauna Kea in Hawaii. The twin Keck reflectors, when used together, have the resolving power of a single telescope 90 meters or 295 feet in diameter. With its very thin atmosphere, the area around the extinct volcano of Mauna Kea is almost perfect for sky watching; a total of nine huge telescopes, with two more under construction, are taking advantage of these ideal conditions. [Aerial view of Mauna Kea showing all the domes] Efforts to create even larger Earth-based telescopes continue. The invention of the rotating furnace allowed Roger Angel to cast an 8-meter or 330-inch mirror for the Large Binocular Telescope to be built in Arizona. The final telescope will have the equivalent light-gathering power of a single 11.8-meter or 464-inch instrument, with the image sharpness of a 22.8-meter or 897-inch mirror, making it the largest telescope anywhere. But despite the great achievements of large ground-based telescopes, there are others who focused on improving our view of outer space by getting rid of the atmosphere's influence altogether. As early as the 1940's, a telescope was proposed that would be completely above the atmosphere. The plan was not to use an even higher mountain, but to place the telescope in outer space itself, positioned in orbit around the Earth and operated by remote control. Today the Hubble Space Telescope is the realization of that dream, although it took many other smaller efforts and projects to make that dream a reality.
