Written by: Bill Herren
Telescopes are observational instruments that give humanity a look at the universe beyond Earth. Since their first use in 1609 by Galileo Galilei, they have contributed greatly to the fields of astronomy and physics. In addition, they have shattered many superstitions and myths about Earth’s place among the stars, such as the geocentric theory of the Earth being the center of the universe. Telescopes have undergone many stages of evolution, from simple two-mirror devices that scanned mountains on the moon, to giant mountain-based observatories and others that now orbit the Earth to study dark energy and hunt for alien planets. Telescopes, ultimately, have brought the potential for great astronomical discovery to the masses, from scientists to amateurs alike.
The History of the Telescope
The first crude telescope, a refractor type, was created by Hans Lippershey, a German-born maker of lenses, who also patented the design in 1608. Italian physicist and astronomer Galileo Galilei then built an improved version in 1609, which he called a “perspicillum.” Two years later, the name “telescope” was given to the device by a math expert named Giovanni Demisiani, which became the word these instruments were known by. German astronomer Johannes Kepler designed a telescope with a pair of convex lenses in the same year, which became known as the “Keplerian telescope.” In 1663, James Gregory, a mathematician from Scotland, designed a reflecting telescope that used mirrors to direct the telescope’s image into an eyepiece. It wasn’t until 1674 that Robert Hooke was able to take Gregor’s design and actually build such a telescope, however the first actual reflector telescope was made by English mathematician Isaac Newton in 1668. Laurent Cassegrain, a French priest, designed a reflecting telescope in 1672 that used a paraboloid mirror with a secondary hyperboloid mirror. This “Cassegrain” design marked the birth of modern telescopes, as the design remained in use even in the 21st century.
In 1729, a lawyer named Chester Moore built a lens that helped to alleviate the type of image distortion known as a chromatic aberration. This was a major breakthrough in improving the quality of telescope observations. In 1789, a German-born composer and astronomer William and Caroline Herschel built the first giant telescope, the Great Forty-Foot Telescope, in England. Another giant telescope, the “Leviathan of Parsonstown,” was built in 1845 Ireland by William Parsons. This telescope was the largest reflector-type telescope, in terms of aperture size, until the Hooker Telescope was completed on Mount Wilson in Los Angeles in 1917. The largest refractor type telescope ever made, in terms of lens diameter, was the Great Paris Exhibition Telescope, built in 1900, and displayed at the Paris 1900 Exposition. The Yerkes telescope in Wisconsin, the second largest ever made, is the largest refractor telescope currently in operation.
Telescopes continued to evolve, but until the 20th century they were all some form of optical telescope, primarily reflector types. In 1931, Karl Jansky, an American-born radio engineer, provided the idea for a radio telescope, which engineer Grote Reber built in 1937. The world’s largest radio telescope is currently the Arecibo Observatory in Puerto Rico, with a 1,000 foot dish. During the 20th century, infrared telescopes also evolved, and due to necessity, some were launched into space, starting with the Infrared Astronomical Satellite (IRAS), which was deployed in space in 1983. In 1990, the Hubble Space Telescope, an optical, infrared and ultraviolet telescope, was launched into space, and is one of the most advanced space-based telescopes currently in operation. Other contemporary advanced telescopes include the Spitzer Space Telescope, the Compton Gamma Ray Observatory, and the Chandra X-ray Observatory.
Different Types & Their Uses
Telescopes come in a variety of design types. The oldest type of telescope is the optical telescope, which is broken up into refractors and reflectors. Refractor telescopes direct light through a series of lenses directly to an eyepiece at the back end, through which an observer can look. Reflector telescopes use mirrors to redirect and focus light. Reflector telescopes overcame refractors in popularity because they produced less serious optical distortions, and this made them much more valuable to astronomers.
In addition to optical telescopes, there are also infrared telescopes, which view the universe by observing infrared energy that is not visible to the naked eye. Infrared telescopes depend on high altitude deployments to reduce absorption of infrared energy by the atmosphere. They produce the best results, however, when launched into space. Radio telescopes, built like giant satellite dishes, scan for radio signals from celestial bodies, which are not absorbed by the atmosphere. They tend to be very large, with dishes up to 1,000 feet in diameter, such as the Aricebo Observatory. X-ray telescopes and ultraviolet telescopes both require high altitudes or deployment in space, and they scan for x-ray radiation and ultraviolet radiation, respectively. X-ray telescopes are good at scanning for black holes and neutron stars, while ultraviolet telescopes provide clues about the evolution of young and old stars, as well as galaxies. Infrared telescopes are used to find celestial bodies such as stars and planets, while optical telescopes observe visible light thrown off by heavenly bodies and galaxies, etcetera. Radio telescopes observe radio wave energy coming from quasars and neutron stars, and are also instrumental in the search for alien life, such as the Search for Extraterrestrial Intelligence project, or SETI.
The Hubble Space Telescope
One of the most celebrated telescopes in history is the Hubble Space Telescope (HST), which was launched into space in 1990. Built with funding from taxpayer dollars and the European Space Agency and NASA, the HST, named after famous astronomer Edwin Hubble, is the only space telescope that was designed for service by astronauts in space. This serviceability proved to be critically useful when it was discovered that its main mirror was defective, requiring service. Another four servicing missions were carried out to replace, repair and upgrade parts in the HST. The HST originally was built with reel-based tape recording instruments, and was upgraded with solid state storage systems. Two times a day the HST transmits its data, a total of 120 gigabytes every week, to a satellite which beams it down to Earth. The data then works its way through White Sands, New Mexico to its final destination at the Goddard Space Flight Center in Greenbelt, Maryland.
Usage of the telescope is technically open to anyone, regardless of their nationality, who can submit a proposal. Amateur astronomers were also invited to participate, but due to budget cuts, only one project was ever approved. Due to intense competition for access to the HST, however, only 20 percent of requests gain approval from the Space Telescope Science Institute. The HST has carried out many projects, including scanning for merging galaxies, measuring the expansion of the universe, and searching for planets outside the solar system. It has also produced a large number of impressive, high quality photographs that have become famous in their own right. The Hubble Telescope is due to reach the end of its life in 2020, at which time it may fall out of orbit or be hauled back to Earth. To facilitate the latter, NASA installed the Soft Capture and Rendezvous System, which is intended to enable a vessel to come and retrieve the HST for recovery or safe disposal.
What Has Been Learned from Telescopes
Telescopes, from the time of Galileo, have completely transformed the entire nature of astronomy. Many superstitious beliefs, such as the Earth being the center of the universe, were disproven by telescopes. Telescopes have found asteroids, planets and moons, planetary rings, and even planets outside the solar system. Galileo used a telescope to measure the height of mountains on the moon as well as discover sunspots. Telescopes revealed the nature of the Milky Way Galaxy, such as when Galileo discovered that the “cloud” among the stars was the galaxy itself, and the cloud was actually made of millions of stars. Using a telescope, an astronomer named Ole Romer discerned the concept of the speed of light. Newton’s use and improvements of telescopes enabled him to make many achievements, including his theories concerning gravity. Edwin Hubble used telescopes to discover that the universe was expanding, and the Hubble Space Telescope, named in his honor, measured the speed of this expansion. Telescopes have also spotted and measured the distances of nebulas, black holes, neutron stars and pulsars, and even giant black holes known as quasars. They are now helping humanity determine the age of the universe, as well as how it formed and evolved, and they are a critical tool in humanity’s search for alien life and potentially habitable worlds outside the star system.
The Hubble telescope discerned the approximate age of the universe to be between 13 and 14 billion years old, caught views of young galaxies from near the beginning of the universe, confirmed the existence of enormous black holes at the center of many galaxies, measured the actual masses and chemical makeup of extrasolar planets, and gave humanity a crystal clear view of the Shoemaker-Levy 9 comet when it hit Jupiter. The Keck Observatory, built on the Mauna Kea volcano in Hawaii in 1990, showed that Mars was emitting methane, and it found the first concrete signs of an extrasolar planet. Its studies of the giant asteroid Eris helped demote Pluto from the status of a planet. The Spitzer Observatory, an infrared telescope, was launched into space in 2003, and was the first to observe light coming from planets outside the solar system. Spitzer also captured what is thought to be the infrared energy signatures of stars from when the universe was just 100 million years old. In 2009 Spitzer, discovered evidence that two extrasolar planets had collided a few thousand years in the past. The Kepler space telescope, deployed in 2009, discovered smaller extrasolar planets, such as one the size of the moon in orbit around the star known as Kepler-37. At the time it was the smallest extrasolar planet ever observed.
The Future of Telescopes
Even after the Hubble was launched, newer and more powerful telescopes were on the drawing board for construction and deployment. For instance, the Transiting Exoplanet Survey (TESS) is a telescope that is scheduled for launch into space in 2017 to hunt for planets outside the solar system. The James Webb Space Telescope is set to launch into a position a million miles above Earth, to study galaxy formation in the earliest years of the universe. The Giant Magellan Telescope is set to become operational in 2020. Based in Chile, it is intended to hunt for extrasolar planets and other very distant celestial bodies. Two years later, in Chile, the Large Synoptic Survey Telescope is planned to come into service, scanning for potentially dangerous asteroids that could impact Earth, as well as building a better map of the Milky Way galaxy. NASA has plans for an Advanced Technology Large-Aperture Space Telescope (ATLAST) to launch into space in 2030. This telescope’s mission will be to scan extrasolar worlds for life, as well as other potential signs of life such as water, methane, and ozone.
In 2020, the ground-based Giant Magellan Telescope is slated to become operational in Chile, and is intended to hunt for extrasolar planets and black holes, and contribute to the study of dark energy. Another telescope planned for construction in Chile, the European Extremely Large Telescope, began construction in 2014 and is being designed to provide direct images of planets outside the solar system, make observations that will answer questions about planet formation, more accurately measure the expansion of the universe, and help scientists with the study of black holes. The Thirty Meter Telescope is an observatory under construction on Mauna Kea in Hawaii, and will engage in a variety of projects, such as studying dark matter, the evolution of galaxies, and searching for signs of life on worlds outside the solar system. The Wide-Field Infrared Survey Telescope (WFIRST) is planned for construction starting in 2017 and for launch into space in 2024. Its mission will be to study dark energy and the expansion of the universe, as well as look for extrasolar planets. The ARKYD Series 100 telescope is a relatively cheap, 33 pound space telescope that is planned for use by private citizens to scan for asteroids within the solar system.
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