telescope

1. An arrangement of lenses or mirrors or both that gathers visible light, permitting direct observation or photographic recording of distant objects.
2. Any of various devices, such as a radio telescope, used to detect and observe distant objects by their emission, transmission, reflection, or other interaction with invisible radiation.

1. To cause to slide inward or outward in overlapping sections, as the cylindrical sections of a small hand telescope do.
2. To make more compact or concise; condense.

[New Latin telescopium or Italian telescopio, both from Greek tēleskopos, far-seeing : tēle-, tele- + skopos, watcher.]

(click to enlarge)
Two types of telescopes. A refracting telescope forms an image by focusing light from a distant … (credit: © Merriam-Webster Inc.)

Device that collects light from and magnifies images of distant objects, undoubtedly the most important investigative tool in astronomy. The first telescopes focused visible light by refraction through lenses; later instruments used reflection from curved mirrors (see optics). Their invention is traditionally credited to Hans Lippershey (1570? – 1619?), who adapted A. van Leeuwenhoek's use of lenses in microscopes. Among the earliest telescopes were Galilean telescopes, modeled after the simple instruments built by Galileo, who was the first to use telescopes to study celestial bodies. In 1611 Johannes Kepler proposed an improved version that became the basis for modern refracting instruments. The reflecting telescope came into its own after William Herschel (see Herschel family) used one to discover the planet Uranus in 1781. Since the 1930s radio telescopes have been used to detect and form images from radio waves emitted by celestial objects. More recently, telescopes have been designed to observe objects and phenomena in other parts of the electromagnetic spectrum (see gamma-ray astronomy; infrared astronomy; ultraviolet astronomy; X-ray astronomy). Spaceflight has allowed telescopes to be launched into Earth orbit to avoid the light-scattering and light-absorbing effects of the atmosphere (e.g., the Hubble Space Telescope). See also binoculars; observatory.

For more information on telescope, visit Britannica.com.

Background

A telescope is a device used to form images of distant objects. The most familiar kind of telescope is an optical telescope, which uses a series of lenses or a curved mirror to focus visible light. An optical telescope which uses lenses is known as a refracting telescope or a refractor; one which uses a mirror is known as a reflecting telescope or a reflector. Besides optical telescopes, astronomers also use telescopes that focus radio waves, X-rays, and other forms of electromagnetic radiation. Telescopes vary in size and sophistication from homemade spyglasses built from cardboard tubes to arrays of house-sized radio telescopes stretching over many miles.

The earliest known telescope was a refractor built by the Dutch eyeglass maker Hans Lippershey in 1608 after he accidentally viewed objects through two different eyeglass lenses held a distance apart. He called his invention a kijker, "looker" in Dutch, and intended it for military use. In 1609, the Italian scientist Galileo Galilei built his own telescopes and was the first person to make astronomical observations using them. These early telescopes consisted of two glass lenses set within a hollow lead tube and were rather small; Galileo's largest instrument was about 47 inches (120 cm) long and 2 inches (5 cm) in diameter. Astronomers such as Johannes Kepler in Germany and Christian Huygens in Holland built larger, more powerful telescopes throughout the 1600s. Soon these telescopes got too large to be easily controlled by hand and required permanent mounts. Some were more than 197 feet (60 m) long.

The ability to construct enormous telescopes outpaced the ability of glassmakers to manufacture appropriate lenses for them. In particular, the problems caused by chromatic aberration (the tendency for a lens to focus each color of light at a different point, leading to a blurred image) became acute for very large telescopes. Scientists of the time knew of no way to avoid this problem with lenses, so they designed telescopes using curved mirrors instead.

In 1663, the Scottish mathematician James Gregory designed the first reflecting telescope. Alternate designs for reflectors were invented by the English scientist Isaac Newton in 1668 and the French scientist N. Cassegrain in 1672. All three designs are still in use today. In the 1600s, there was no good way to coat glass with a thin reflective film, as is done today to make mirrors, so these early reflectors used mirrors made out of polished metal. Newton used a mixture of copper, tin, and arsenic to produce a mirror which could only reflect 16% of the light it received; today's mirrors reflect nearly 100% of the light that hits them.

It had been known as early as 1730 that chromatic aberration could be minimized by replacing the main lens of the telescope with two properly shaped lenses made from two different kinds of glass, but it was not until the early 1800s that the science of glassmaking was advanced enough to make this technique practical. By the end of the 19th century, refracting telescopes with lenses up to a meter in diameter were constructed, and these are still the largest refracting telescopes in operation.

Reflectors once again dominated refractors in the 20th century, when techniques for constructing very large, very accurate mirrors were developed. The world's largest optical telescopes are all reflectors, with mirrors up to 19 feet (6 m) in diameter.

Raw Materials

A telescope consists of an optical system (the lenses and/or mirrors) and hardware components to hold the optical system in place and allow it to be maneuvered and focused. Lenses must be made from optical glass, a special kind of glass which is much purer and more uniform than ordinary glass. The most important raw material used to make optical glass is silicon dioxide, which must not contain more than one-tenth of one percent (0.1%) of impurities.

Optical glasses are generally divided into crown glasses and flint glasses. Crown glasses contain varying amounts of boron oxide, sodium oxide, potassium oxide, barium oxide, and zinc oxide. Flint glasses contain lead oxide. The antireflective coating on telescope lenses is usually composed of magnesium fluoride.

A telescope mirror can be made from glass that is somewhat less pure than that used to make a lens, since light does not pass through it. Often a strong, temperature-resistant glass such as Pyrex is used. Pyrex is a brand name for glass composed of silicon dioxide, boron oxide, and aluminum oxide. The reflective coating for telescope mirrors is usually made from aluminum, and the protective coating on top of the reflective coating is usually composed of silicon dioxide.

Hardware components that are directly involved with the optical system are usually manufactured from steel or steel and zinc alloys. Less critical parts can be made from light, inexpensive materials such as aluminum or acrylonitrile-butadiene-styrene plastic, commonly called ABS.

The Manufacturing
Process

Making the hardware components

• Metal hardware components are manufactured using standard metalworking machines such as lathes and drill presses.
• Components made from ABS plastics (usually the external body of the telescope) are produced using a technique known as injection molding. In this process the plastic is melted and forced under pressure into a mold in the shape of the final product. The plastic is allowed to cool back into a solid, and the mold is opened to allow the component to be removed.

Making optical glass

• The glass manufacturer mixes the proper raw materials with waste glass of the same type as the glass to be made. This waste glass, known as cullet, acts as a flux; that is, it causes the raw materials to react together at a lower temperature than they would without it.
• This mixture is heated in a glass furnace until it has melted into a liquid. The temperature needed to form molten glass varies with the type of glass being made, but it is typically about 2550°F (1400°C).
• The temperature of the molten glass is raised to about 2820°F (1550°C) to force air bubbles to come to the surface. It is then allowed to cool while being stirred constantly until it has reached about 1830°F (1000°C), at which point it is an extremely thick fluid. This viscous, molten glass is poured into molds with roughly the same shape as the lenses required.
• After the glass has cooled to about 570°F (300°C), it must be reheated to about 1020°F (550°C) to remove internal stresses that form during the initial cooling period and which weaken the glass. It is then allowed to cool slowly to room temperature. This process is known as annealing. The final lens-shaped chunks of glass are known as blanks.

Making the lenses

The blanks are processed by the telescope manufacturer in three steps: cutting, grinding, and polishing. A mirror is formed in exactly the same way as a lens until the reflective coating is applied.

• First a high-speed, rotating cylindrical cutter with a round diamond blade, known as a curve generator, shaves the surface of the lens until a close approximation of the desired curve is achieved. The cut lens is inspected with a spherometer to check the curvature and is recut if necessary. The time required for cutting varies greatly with the type of glass being cut and the kind of lens being shaped. A lens may require several cuttings, each of which may take anywhere from a few minutes to more than half an hour.
• Several cut blanks are placed on a curved block in such a way that their surfaces line up as if they were all part of one large spherical curve. This is necessary so that the grinding machine can grind them all in the same way. A cast iron grinding surface known as a tool is pressed onto them. During grinding, the block of lenses rotates while the tool is free to move at random on top of it. Between the tool and the block flows a slurry containing water, an abrasive to do the grinding (usually silicon carbide), a coolant to prevent the lenses from being damaged by overheating, and a surfactant to keep the abrasive from settling out. The speed at which the block rotates, the force placed on the lenses, the exact contents of the slurry, and other variables are controlled by experienced opticians to produce the exact type of lens desired. Each lens is once again inspected with a spherometer and reground if necessary. The total grinding process may take anywhere from one hour to eight hours. The ground lenses are cleaned and moved to the polishing room.
• The polishing machine is similar to the grinding machine, but the tool is made from pitch—a thick, soft, resinous substance derived from coal tar or wood tar. A pitch tool is made by placing tape around the circumference of a curved dish, pouring in hot, liquid pitch with other ingredients such as beeswax and jeweler's rouge, and letting it cool back into a solid. A pitch tool can polish about 50 lenses before it must be reshaped. Polishing proceeds in the same manner as grinding, but instead of an abrasive the slurry contains a polishing substance, usually cerium dioxide, in the form of a very fine pink powder. The polished lenses are optically inspected and repolished if necessary. The polishing procedure may take anywhere from half an hour to four or five hours. The lenses are cleaned and are ready for coating.

Applying coatings

• To make a lens into a mirror, a very thin, very smooth coating of aluminum is applied. Aluminum is heated in a vacuum to form a vapor. A negative electro-static charge is applied to the surface of the lens so that the positively charged aluminum ions are attracted to it. Similar procedures are followed to apply a coating of silicon dioxide to protect the fragile surface of a mirror or to apply an antireflective coating of magnesium fluoride to the surface of a lens. The finished lens or mirror is inspected, labeled with a date of manufacture and a serial number, and stored until needed.

Assembling and shipping the telescope

• The hardware components, lenses, and mirrors required to make a particular model of telescope are assembled by hand in an assembly line process. The completed telescope is packed with close-fitting expanded polystyrene foam to protect it from damage during shipping. The telescope is packed in a cardboard box and shipped to the retailer or consumer.

Quality Control

The most critical aspect of quality control for an optical telescope is the accuracy of the lenses and mirrors. During the cutting and grinding stages, the physical dimensions of the lens are measured very carefully. The thickness and the diameter of the lens are measured with a vernier caliper, an instrument which looks something like a monkey wrench. The outer, fixed jaw of the caliper is placed against one side of the lens and the inner, sliding jaw is gently moved until it meets the other side of the lens. In a classic vernier caliper, the dimensions of the lens are read very accurately using a scale which moves along with the inner jaw and which is compared with a stationary scale attached to the outer jaw. This type of caliper works much like a slide rule. There also exist electronic versions of this instrument, in which the measured dimension automatically appears on a digital display.

The curvature of a lens is measured with a spherometer, a device which resembles a pocket watch with three small pins protruding from its base. The outer two pins are fixed in place while the inner pin is free to move in and out. The spherometer is gently placed on the surface of the lens. Depending on the type of curve, the middle pin will either be higher than the other two pins or lower than the other two pins. The movement of the inner pin moves a needle on a calibrated dial on the face of the spherometer. This value is compared with the standard value that should be obtained for the desired curvature.

Tolerances vary with the type of lens being manufactured, but a typical acceptable variation might be plus or minus 0.0008 inches (20 micrometers). For a flat lens, generally one destined to become a flat mirror, the tolerance is much smaller, usually about plus or minus 0.00004 inches (1.0 micrometer).

During the polishing stage, these instruments are not accurate enough to ensure that the lens will work properly. Optical tests, which measure the way light is affected by the lens, must be used. One common test is known as an autocollimation test. The lens is placed in a dark room and is illuminated with a low intensity pinpoint light source. A diffraction grating (a surface containing thousands of microscopic parallel grooves per inch) is placed at the point where the lens should focus light. The grating causes an interference pattern of dark and light lines to form in front of and behind the focal point. The true focal point can thus be found precisely and compared with the theoretical focal point for the type of lens desired.

In order to test a flat lens, a lens that is known to be flat is placed face down on the lens that is to be tested, which rests on a piece of black felt. The microscopic gaps between the two lenses cause an interference pattern to appear when gentle pressure is applied. The light and dark lines are known as Newton's rings. If the lens being tested is flat, the lines should be straight and regular. If the lens is not flat, the lines will be curved.

The Future

The techniques used to produce excellent lenses and mirrors have been well under-stood for many years, and major innovations in this area are unlikely. One area of active research is in coating technology. New coating substances may be developed to provide better protection for mirrors and better prevention of loss of light through reflection for lenses.

A more dramatic area of progress is in the electronic accessories that accompany telescopes. Amateur astronomers will soon be able to obtain telescopes with built-in computer guidance systems that will enable them to automatically point the telescope at a selected celestial object and to track it night by night. They will also be able to attach video cameras to their telescopes and film such astronomical phenomena as lunar eclipses and the movements of planets and moons.

Where To Learn More

Books

Asimov, Isaac. Eyes on the Universe: A History of the Telescope. Houghton Mifflin, 1975.

Bell, Louis. The Telescope. Dover, 1981.

Manly, Peter L. Unusual Telescopes. Cambridge University Press, 1991.

Periodicals

Mullins, Mark. "A Truly Economical Telescope." Sky and Telescope, December 1993, pp. 91-92.

Nash, J. Madeleine. "Shoot for the Stars." Time, April 27, 1992, pp. 56-57.

Nelson, Ray. "Reinventing the Telescope." Popular Science, January 1995, pp. 57-59, 85.

[Article by: Rose Secrest]

An instrument used to collect, measure, or analyze electromagnetic radiation from distant objects. A telescope overcomes the limitations of the eye by increasing the ability to see faint objects and discern fine details. In addition, when used in conjunction with modern detectors, a telescope can “see” light that is otherwise invisible. The wavelength of the light of interest can have a profound effect on the design of a telescope. See also Electromagnetic radiation; Light.

For many applications, the Earth's atmosphere limits the effectiveness of larger telescopes. The most obvious deleterious effect is image scintillation and motion, collectively known as poor seeing. Atmospheric turbulence produces an extremely rapid motion of the image resulting in a smearing. On the very best nights at ideal observing sites, the image of a star will be spread out over a 0.25-arcsecond seeing disk; on an average night, the seeing disk may be between 0.5 and 2.0 arcseconds.

The upper atmosphere glows faintly because of the constant influx of charged particles from the Sun. The combination of the finite size of the seeing disk of stars and the presence of airglow limits the telescope's ability to see faint objects. One solution is placing a large telescope in orbit above the atmosphere. In practice, the effects of air and light pollution outweigh those of airglow at most observatories in the United States. See also Airglow.

There are basically three types of optical systems in use in astronomical telescopes: refracting systems whose main optical elements are lenses which focus light by refraction; reflecting systems, whose main imaging elements are mirrors which focus light by reflection; and catadioptric systems, whose main elements are a combination of a lens and a mirror. The most notable example of the last type is the Schmidt camera.

Astronomers seldom use large telescopes for visual observations. Instead, they record their data for future study. Modern developments in photoelectric imaging devices are supplanting photographic techniques for many applications. The great advantages of detectors such as charge-coupled devices is their high sensitivity, and the images can be read out in a computer-compatible format for immediate analysis. See also Charge-coupled devices.

Light received from most astronomical objects is made up of radiation of all wavelengths. The spectral characteristics of this radiation may be extracted by special instruments called spectrographs. See also Astronomical spectroscopy.

As collectors of radiation from a specific direction, telescopes may be classified as focusing and nonfocusing. Nonfocusing telescopes are used for radiation with energies of x-rays and above (x-ray, gamma-ray, cosmic-ray, and neutrino telescopes). Focusing telescopes, intended for nonvisible wavelengths, are similar to optical ones (solar, radio, infrared, and ultraviolet telescopes), but they differ in the details of construction. See also Cerenkov radiation; Cosmic rays; Gamma-ray astronomy; Infrared astronomy; Neutrino astronomy; Radio telescope; Sun; Ultraviolet astronomy; X-ray telescope.

The 5-m (200-in.) Hale telescope at Palomar Mountain, California, was completed in 1950. The primary mirror is 5 m in diameter with a 1.02-m (40-in.) hole in the center.

The 4-m (158-in.) Mayall reflector at the Kitt Peak National Observatory was dedicated in 1973. The prime focus has a field of view six times greater than that of the Hale reflector. An identical telescope was subsequently installed at Cerro Tololo Inter-American Observatory, in Chile.

The mirrors for these traditional large telescopes were all produced using the same general methodology. A large, thick glass mirror blank was first cast; then the top surface of the mirror was laboriously ground and polished to the requisite shape. The practical and economical limit to the size of traditional mirror designs was nearly reached by the 6-m (236-in.) telescope in the Caucasus Mountains, Russia. Newer telescopes have been designed and built that use either a number of mirrors mounted such that the light collection by them is brought to a common focus, or lightweight mirrors in computer-controlled mounts.

The Keck Telescope on Mauna Kea, Hawaii, completed in 1993, is the largest of the segmented mirror telescopes to be put into operation. The telescope itself is a fairly traditional design. However, its primary mirror is made up of 36 individual hexagonal segments mosaiced together to form a single 10-m (386-in.) mirror. Electronic sensors built into the edges of the segments monitor the relative positions of the segments, and feed the results to a computer-controlled actuator system.

In 1989, the European Southern Observatory put into operation their New Technology Telescope. The 3.58-m (141-in.) mirror was produced by a technique known as spin-casting, where molten glass is poured into a rotating mold.

Worldwide efforts are under way on a new generation of large, ground-based telescopes, using both the spin-casting method and the segmented method to produce large mirrors. The Gemini project of the National Optical Astronomy Observatories is building twin 8.1-m (319-in.) telescopes, Gemini North on Mauna Kea, Hawaii (1999), and Gemini South on Cerro Pachon in Chile (2000).

The Very Large Telescope (VLT), operated by the European Southern Observatory on Cerro Paranel, Chile, consists of four 8-m (315-in.) “unit” telescopes with spin-cast mirrors. The light from the four telescopes is combined to give the equivalent light-gathering power of a 16-m (630-in.) telescope. The last of the four telescopes began collecting scientific data in September 2000.

The ability of large telescopes to resolve fine detail is limited by a number of factors. Distortion due to the mirror's own weight causes problems in addition to those of atmospheric seeing. The Earth-orbiting Hubble Space Telescope, (HST) with an aperture of 2.4 m (94 in.), was designed to eliminate these problems. The telescope operates in ultraviolet as well as visible light, resulting in a great improvement in resolution not only by the elimination of the aforementioned terrestrial effects but by the reduced blurring by diffraction in the ultraviolet. See also Diffraction; Resolving power (optics).

Soon after the telescope was launched in 1990, it was discovered that the optical system was plagued with spherical aberration, which severely limited its spatial resolution. After space-shuttle astronauts serviced and repaired the telescope in 1993, adding what amounted to eyeglasses for the scientific instruments, the telescope exceeded its prelaunch specifications for spatial resolution. Subsequent servicing missions replaced instruments with newer technology. See also Space Telescope, Hubble.

n.

A device having a relation to the eye similar to that of the telephone to the ear, enabling distant objects to plague us with a multitude of needless details. Luckily it is unprovided with a bell summoning us to the sacrifice.

Dreaming about a telescope can represent the need to take a closer look at something. Alternatively, it could represent exaggerating something, making it bigger than it actually is.

A device used by astronomers to magnify images or collect more light from distant objects by gathering and concentrating radiation. The most familiar kind of telescope is the optical telescope, which collects radiation in the form of visible light. It may work by reflection, with a bowl-shaped mirror at its base, or by refraction, with a system of lenses. Other kinds of telescopes collect other kinds of radiation; there are radio telescopes (which collect radio waves), x-ray telescopes, and infrared telescopes. Radio and optical telescopes may be situated on the Earth, since the Earth's atmosphere allows light and radio waves through but absorbs radiation from several other regions of the electromagnetic spectrum. X-ray telescopes are placed in space.

For other uses, see Telescope (disambiguation).

The 100 inch (2.5 m) Hooker reflecting telescope at Mount Wilson Observatory near Los Angeles, California.

A telescope is an instrument designed for the observation of remote objects by the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century. "Telescopes" can refer to a whole range of instruments operating in most regions of the electromagnetic spectrum.

The word "telescope" (from the Greek τῆλε, tele "far" and σκοπεῖν, skopein "to look or see"; τηλεσκόπος, teleskopos "far-seeing") was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei's instruments presented at a banquet at the Accademia dei Lincei.^[1][2][3] In the Starry Messenger Galileo had used the term "perspicillum".

Contents 1 History 2 Types of telescopes 2.1 Optical telescopes 2.2 Radio telescopes 2.3 High energy particle telescopes 2.4 Other types of telescopes 3 Lists of telescopes 4 See also 5 Notes 6 References 7 External links

History

Main article: History of the telescope

The earliest evidence of working telescopes were the refracting telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar.^[4] Galileo greatly improved upon these designs the following year.

The idea that a mirror could be used as an objective instead of a lens was being investigated soon after the invention of the refracting telescope.^[5] The potential advantages of using parabolic mirrors, primarily reduction of spherical aberration with no chromatic aberration, led to many proposed designs and several attempts to build reflecting telescopes.^[6] In 1668, Isaac Newton built the first practical reflecting telescope, which bears his name, the Newtonian reflector.

The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes. Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by the introduction of silver coated glass mirrors in 1857,^[7] and aluminized mirrors in 1932.^[8] The maximum physical size limit for refracting telescopes is about 1 meter (40 inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors. The largest reflecting telescopes currently have objectives larger then 10 m (33 feet).

The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937. Since then, a tremendous variety of complex astronomical instruments have been developed.

Types of telescopes

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The name "telescope" covers a wide range of instruments and is difficult to define. They all have the attribute of collecting electromagnetic radiation so it can be studied or analyzed in some manner. The most common type is the optical telescope; other types also exist and are listed below.

Optical telescopes

50 cm refracting telescope at Nice Observatory.

Main article: Optical telescope

An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum (although some work in the infrared and ultraviolet). Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness. In order for the image to be observed, photographed, studied, and sent to a computer, telescopes work by employing one or more curved optical elements—usually made from glass—lenses, or mirrors to gather light and other electromagnetic radiation to bring that light or radiation to a focal point. Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits), spotting scopes, monoculars, binoculars, camera lenses, and spyglasses. There are three main types:

• The refracting telescope which uses lenses to form an image.
• The reflecting telescope which uses an arrangement of mirrors to form an image.
• The catadioptric telescope which uses mirrors combined with lenses to form an image.

Other optical telescopes:

• Infrared telescopes
• Submillimetre telescopes
• Ultraviolet telescopes
• Fresnel Imager

Radio telescopes

Main article: Radio telescope

The Very Large Array at Socorro, New Mexico, United States.

Radio telescopes are directional radio antennas used for radio astronomy. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed. Multi-element Radio telescopes are constructed from pairs or larger groups of these dishes to synthesize large 'virtual' apertures that are similar in size to the separation between the telescopes; this process is known as aperture synthesis. As of 2005, the current record array size is many times the width of the Earth—utilizing space-based Very Long Baseline Interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite. Aperture synthesis is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and aperture masking interferometry at single reflecting telescopes. Radio telescopes are also used to collect microwave radiation, which is used to collect radiation when any visible light is obstructed or faint, such as from quasars. Some radio telescopes are used by programs such as SETI and the Arecibo Observatory to search for exterrestrial life.

High energy particle telescopes

The Einstein Observatory, an X-ray telescope originally named the HEAO B (High Energy Astrophysical Observatory B)

High-energy astronomy requires specialized telescopes to make observations since most of these particles go through most metals and glasses.

X-ray telescopes use Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to reflect the rays just a few degrees. The mirrors are usually a section of a rotated parabola and a hyperbola, or ellipse. In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror.^[9][10]

Gamma-ray telescopes refrain from focusing completely and use coded aperture masks: the patterns of the shadow the mask creates can be reconstructed to form an image.

X-ray and Gamma-ray telescopes are usually on Earth-orbiting satellites or high-flying balloons since the Earth's atmosphere is opaque to this part of the electromagnetic spectrum.

In other types of high energy particle telescopes there is no image-forming optical system. Cosmic-ray telescopes usually consist of an array of different detector types spread out over a large area. A Neutrino telescope consists of a large mass of water or ice, surrounded by an array of sensitive light detectors known as photomultiplier tubes.

Other types of telescopes

• Gravitational wave telescopes

A diagram of the electromagnetic spectrum with the Earth's atmospheric transmittance (or opacity) and the types of telescopes used to image parts of the spectrum.

Lists of telescopes

• List of optical telescopes
• List of largest optical reflecting telescopes
• List of largest optical refracting telescopes
• List of largest optical telescopes historically
• list of radio telescopes
• List of space telescopes
• List of solar telescopes
• List of telescope types
• Category:Telescopes
• Category:Cosmic-ray telescopes
• Category:Gamma-ray telescopes
• Category:Gravitational wave telescopes
• Category:High energy particle telescopes
• Category:Infrared telescopes
• Category:Submillimetre telescopes
• Category:Ultraviolet telescopes
• Category:X-ray telescopes

See also

Wikimedia Commons has media related to: Telescopes

A group of Newtonian Telescopes at Perkins Observatory, Delaware, Ohio

• Amateur telescope making
• Angular resolution
• Aperture synthesis
• ASCOM open standards for computer control of telescopes
• Depth of field
• Dynameter
• f-number
• First light
• Bahtinov mask
• Carey mask
• Hartmann mask
• Keyhole problem
• Microscope
• Nimrud lens
• Remote Telescope Markup Language
• Robotic telescope
• Timeline of telescope technology
• Timeline of telescopes, observatories, and observing technology

Notes

1. ^ archive.org "Galileo His Life And Work" BY J. J. FAHIE "Galileo usually called the telescope occhicde or cannocchiale ; and now he calls the microscope occhialino. The name telescope was first suggested by Demisiani in 1612"
2. ^ Sobel (2000, p.43), Drake (1978, p.196)
3. ^ Rosen, Edward, The Naming of the Telescope (1947)
4. ^ galileo.rice.edu The Galileo Project > Science > The Telescope by Al Van Helden "The Hague discussed the patent applications first of Hans Lipperhey of Middelburg, and then of Jacob Metius of Alkmaar... another citizen of Middelburg, Sacharias Janssen had a telescope at about the same time but was at the Frankfurt Fair where he tried to sell it"
5. ^ Stargazer - By Fred Watson, Inc NetLibrary, Page 109
6. ^ Attempts by Niccolò Zucchi and James Gregory and theoretical designs by Bonaventura Cavalieri, Marin Mersenne, and Gregory among others
7. ^ madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868)
8. ^ Bakich sample pages Chapter 2, Page 3 "John Donavan Strong, a young physicist at the California Institute of Technology, was one of the first to coat a mirror with aluminum. He did it by thermal vacuum evaporation. The first mirror he aluminized, in 1932, is the earliest known example of a telescope mirror coated by this technique."
9. ^ Wolter, H. (1952). "Glancing Incidence Mirror Systems as Imaging Optics for X-rays". Ann. Physik 10: 94. 
10. ^ Wolter, H. (1952). "A Generalized Schwarschild Mirror Systems For Use at Glancing Incidence for X-ray Imaging". Ann. Physik 10: 286. 

References

• Contemporary Astronomy - Second Edition, Jay M. Pasachoff, Saunders Colleges Publishing - 1981, ISBN 0-03-057861-2
• Elliott, Robert S. (1966), Electromagnetics, McGraw-Hill 
• Rashed, Roshdi; Morelon, Régis (1996), Encyclopedia of the History of Arabic Science, 1 & 3, Routledge, ISBN 0415124107 
• Wade, Nicholas J.; Finger, Stanley (2001), "The eye as an optical instrument: from camera obscura to Helmholtz's perspective", Perception 30 (10): 1157–1177 
• Sabra, A. I. & Hogendijk, J. P. (2003), The Enterprise of Science in Islam: New Perspectives, MIT Press, pp. 85–118, ISBN 0262194821

External links

• The Galileo Project - The Telescope by Al Van Helden
• "The First Telescopes". Part of an exhibit from Cosmic Journey: A History of Scientific Cosmology by the American Institute of Physics
• Timeline of telescopic technology

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - teleskop, kikkert
v. tr. - klemme sammen, skyde sammen, forkorte
v. intr. - blive skudt sammen , blive trukket sammen

Nederlands (Dutch)
(astronomische) verrekijker, verkorten

Français (French)
n. - télescope
v. tr. - (lit) replier, (fig) condenser, se télescoper
v. intr. - être télescopique, se télescoper

Deutsch (German)
n. - Teleskop, Fernrohr
v. - (sich) ineinanderschieben, verkürzen

Ελληνική (Greek)
n. - (οπτ.) τηλεσκόπιο
v. - συμπτύσσομαι (τηλεσκοπικώς), γίνομαι φυσαρμόνικα

Italiano (Italian)
telescopio

Português (Portuguese)
n. - telescópio (m), óculo (m)
v. - encurtar, condensar, encaixar-se (vagões)

Русский (Russian)
телескоп, выдвижная зрительная труба, оптический прицел

Español (Spanish)
n. - telescopio
v. tr. - hacer entrar o empotrarse (una cosa en otra) , acortar, simplificar
v. intr. - enchufarse, entrar, empotrarse (una cosa en otra)

Svenska (Swedish)
n. - teleskop, kikare
v. - skjuta ihop, skjuta in (i varandra)

中文（简体）(Chinese (Simplified))
望远镜, 缩叠式旅行袋, 使套叠, 缩短, 使相嵌, 嵌进, 挤撞

中文（繁體）(Chinese (Traditional))
n. - 望遠鏡, 縮疊式旅行袋
v. tr. - 使套疊, 縮短, 使相嵌
v. intr. - 嵌進, 縮短, 擠撞

한국어 (Korean)
n. - 망원경, 확대 광학 기계, 망원경 자리
v. tr. - 끼워 넣다, 겹 쌓이게 하다, 짧게 하다
v. intr. - 끼워 넣어지다, 충돌하여 포개어지다

日本語 (Japanese)
n. - 望遠鏡
v. - …がはまり込む, 圧縮される

العربيه (Arabic)
‏(الاسم) المقراب, التلسكوب (فعل) يوجز, يضغط, يجعله يتداخل‏

עברית (Hebrew)
n. - ‮טלסקופ‬
v. tr. - ‮צימצם, כיווץ‬
v. intr. - ‮התקצר, נמעך, נלחץ זה לתוך זה‬

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