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A primary mirror (or primary) is the principal light-gathering surface (the objective) of a reflecting telescope.
| | This article needs additional citations for verification .(November 2023) |
A primary mirror (or primary) is the principal light-gathering surface (the objective) of a reflecting telescope.
The primary mirror of a reflecting telescope is a spherical or parabolic shaped disks of polished reflective metal (speculum metal up to the mid 19th century), or in later telescopes, glass or other material coated with a reflective layer. One of the first known reflecting telescopes, Newton's reflector of 1668, used a 3.3 cm polished metal primary mirror. The next major change was to use silver on glass rather than metal, in the 19th century such was with the Crossley reflector. This was changed to vacuum deposited aluminum on glass, used on the 200-inch Hale telescope.
Solid primary mirrors have to sustain their own weight and not deform under gravity, which limits the maximum size for a single piece primary mirror.
Segmented mirror configurations are used to get around the size limitation on single primary mirrors. For example, the Giant Magellan Telescope will have seven 8.4 meter primary mirrors, with the resolving power equivalent to a 24.5 m (80.4 ft) optical aperture. [2]
The largest optical telescope in the world as of 2009 to use a non-segmented single-mirror as its primary mirror is the 8.2 m (27 ft) Subaru telescope of the National Astronomical Observatory of Japan, located in Mauna Kea Observatory on Hawaii since 1997; [3] [ better source needed ] however, this is not the largest diameter single mirror in a telescope, the U.S./German/Italian Large Binocular Telescope has two 8.4 m (28 ft) mirrors (which can be used together for interferometric mode). [4] Both of these are smaller than the 10 m segmented primary mirrors on the dual Keck telescope. The Hubble Space Telescope has a 2.4 metres (7 feet 10 inches) primary mirror.
Radio and submillimeter telescopes use much larger dishes or antennae, which do not have to be made as precisely as the mirrors used in optical telescopes. The Arecibo Telescope used a 305 m dish, which was the world largest single-dish radio telescope fixed to the ground. [5] [6] The Green Bank Telescope has the world's largest steerable single radio dish with 100 m in diameter. [7] There are larger radio arrays, composed of multiple dishes which have better image resolution but less sensitivity. [8]
A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects, just as optical telescopes are the main observing instrument used in traditional optical astronomy which studies the light wave portion of the spectrum coming from astronomical objects. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.
A parabolicreflector is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis. The parabolic reflector transforms an incoming plane wave travelling along the axis into a spherical wave converging toward the focus. Conversely, a spherical wave generated by a point source placed in the focus is reflected into a plane wave propagating as a collimated beam along the axis.
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have 10 m (33 ft) aperture primary mirrors, and when completed in 1993 and 1996 were the largest optical reflecting telescopes in the world. They are currently the 3rd and 4th largest.
The history of the telescope can be traced to before the invention of the earliest known telescope, which appeared in 1608 in the Netherlands, when a patent was submitted by Hans Lippershey, an eyeglass maker. Although Lippershey did not receive his patent, news of the invention soon spread across Europe. The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. Galileo improved on this design the following year and applied it to astronomy. In 1611, Johannes Kepler described how a far more useful telescope could be made with a convex objective lens and a convex eyepiece lens. By 1655, astronomers such as Christiaan Huygens were building powerful but unwieldy Keplerian telescopes with compound eyepieces.
A reflecting telescope is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a catoptric telescope.
Speculum metal is a mixture of around two-thirds copper and one-third tin, making a white brittle alloy that can be polished to make a highly reflective surface. It was used historically to make different kinds of mirrors from personal grooming aids to optical devices until it was replaced by more modern materials such as metal-coated glass mirrors.
The Hale Telescope is a 200-inch (5.1 m), f/3.3 reflecting telescope at the Palomar Observatory in San Diego County, California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, design, and construction of the observatory, but with the project ending up taking 20 years he did not live to see its commissioning. The Hale was groundbreaking for its time, with double the diameter of the second-largest telescope, and pioneered many new technologies in telescope mount design and in the design and fabrication of its large aluminum coated "honeycomb" low thermal expansion Pyrex mirror. It was completed in 1949 and is still in active use.
The Giant Magellan Telescope is a 25.4-meter, ground-based, extremely large telescope under construction at Las Campanas Observatory in Chile's Atacama Desert. Commissioning is anticipated in the late 2020s. Once complete, the Giant Magellan will be the largest Gregorian telescope ever built observing in optical and mid-infrared light. The telescope uses seven of the world’s largest mirrors to form a light collecting area of 368 square meters.
The Special Astrophysical Observatory of the Russian Academy of Science is an astronomical observatory, set up in 1966 in the USSR, and now operated by the Russian Academy of Sciences. Based in the Bolshoi Zelenchuk Valley of the Greater Caucasus near the village of Nizhny Arkhyz, the observatory houses the BTA-6 and RATAN-600, an optical and radio telescope, respectively. The two instruments are about 20 km (12 mi) apart.
Mount Lemmon Observatory (MLO), also known as the Mount Lemmon Infrared Observatory, is an astronomical observatory located on Mount Lemmon in the Santa Catalina Mountains approximately 28 kilometers (17 mi) northeast of Tucson, Arizona (US). The site in the Coronado National Forest is used with special permission from the U.S. Forest Service by the University of Arizona's Steward Observatory, and contains a number of independently managed telescopes.
The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke. James Gregory was a contemporary of Isaac Newton. Both often worked simultaneously on similar projects. Gregory's design was published in 1663 and pre-dates the first practical reflecting telescope, the Newtonian telescope, built by Sir Isaac Newton in 1668. However, Gregory's design was only a theoretical description, and he never actually constructed the telescope. It was not successfully built until five years after Newton's first reflecting telescope.
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric. They are used as objectives for large reflecting telescopes. To function, all the mirror segments have to be polished to a precise shape and actively aligned by a computer-controlled active optics system using actuators built into the mirror support cell.
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally it was an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects – an optical telescope. Nowadays, the word "telescope" is defined as wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.
The Five-hundred-meter Aperture Spherical Telescope, nicknamed Tianyan, is a radio telescope located in the Dawodang depression (大窝凼洼地), a natural basin in Pingtang County, Guizhou, southwest China. FAST has a 500 m (1,600 ft) diameter dish constructed in a natural depression in the landscape. It is the world's largest filled-aperture radio telescope and the second-largest single-dish aperture, after the sparsely-filled RATAN-600 in Russia.
An extremely large telescope (ELT) is an astronomical observatory featuring an optical telescope with an aperture for its primary mirror from 20 metres up to 100 metres across, when discussing reflecting telescopes of optical wavelengths including ultraviolet (UV), visible, and near infrared wavelengths. Among many planned capabilities, extremely large telescopes are planned to increase the chance of finding Earth-like planets around other stars. Telescopes for radio wavelengths can be much bigger physically, such as the 300 metres aperture fixed focus radio telescope of the Arecibo Observatory. Freely steerable radio telescopes with diameters up to 100 metres have been in operation since the 1970s.
The Arecibo Telescope was a 305 m (1,000 ft) spherical reflector radio telescope built into a natural sinkhole at the Arecibo Observatory located near Arecibo, Puerto Rico. A cable-mount steerable receiver and several radar transmitters for emitting signals were mounted 150 m (492 ft) above the dish. Completed in November 1963, the Arecibo Telescope was the world's largest single-aperture telescope for 53 years, until it was surpassed in July 2016 by the Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou, China.