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63-695: The telescope had a first light in 1998, and is a noted robotic telescope. It had first recorded data in August 1996, and was formally dedicated late that year. It was used for the Lick Observatory Supernova Search. The KAIT is a computer-controlled reflecting telescope with a 76 cm mirror and a CCD camera to take pictures. It is located at the Lick Observatory near San Jose, California . KAIT can take close to 100 images per hour and observe about 1000 galaxies

126-407: A Type Ia supernova . In 2019, KAIT was one of the telescopes whose data was used in a study on Blazars . Reflecting telescope A reflecting telescope (also called a reflector ) 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

189-464: A 6 feet (1.8 m) wide metal mirror. In the 19th century a new method using a block of glass coated with very thin layer of silver began to become more popular by the turn of the century. Common telescopes which led to the Crossley and Harvard reflecting telescopes, which helped establish a better reputation for reflecting telescopes as the metal mirror designs were noted for their drawbacks. Chiefly

252-524: A Nasmyth-style telescope to deliver the light (usually through the declination axis) to a fixed focus point that does not move as the telescope is reoriented gives a coudé focus (from the French word for elbow). The coudé focus gives a narrower field of view than a Nasmyth focus and is used with very heavy instruments that do not need a wide field of view. One such application is high-resolution spectrographs that have large collimating mirrors (ideally with

315-638: A concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image, useful for terrestrial observations. Some small spotting scopes are still built this way. There are several large modern telescopes that use a Gregorian configuration such as the Vatican Advanced Technology Telescope , the Magellan telescopes , the Large Binocular Telescope , and

378-403: A desired paraboloid shape that requires minimal grinding and polishing to reach the exact figure needed. Reflecting telescopes, just like any other optical system, do not produce "perfect" images. The need to image objects at distances up to infinity, view them at different wavelengths of light, along with the requirement to have some way to view the image the primary mirror produces, means there

441-476: A few larger ones. After Keeler died unexpectedly in 1900, William W. Campbell , now Lick Observatory's astronomer-in-charge, assigned Assistant Astronomer Charles Dillon Perrine "to take charge of all duties in connection with the Crossley" including completing Keeler's observation of the near-Earth asteroid 433 Eros , for the determination of the solar parallax . Perrine further significantly reconstructed

504-426: A hole in the primary. The folding and diverging effect of the secondary mirror creates a telescope with a long focal length while having a short tube length. The Ritchey–Chrétien telescope, invented by George Willis Ritchey and Henri Chrétien in the early 1910s, is a specialized Cassegrain reflector which has two hyperbolic mirrors (instead of a parabolic primary). It is free of coma and spherical aberration at

567-482: A mirror by A.A. Common, or the 1 Meter Spiegelteleskop (39.4 inch reflector) of the Hamburg Observatory . At this time the 72-inch Leviathan of Parsonstown was the largest by aperture, but it used a metal mirror. Despite the accomplishments of reflectors under Herschel, in the 19th century much of the astronomical community used relatively small refractors, often just a few inches in aperture, save for

630-408: A moderate field of view. A 6" (150mm) f/15 telescope offers a maximum 0.75 degree field of view using 1.25" eyepieces. A number of variations are common, with varying numbers of mirrors of different types. The Kutter (named after its inventor Anton Kutter ) style uses a single concave primary, a convex secondary and a plano-convex lens between the secondary mirror and the focal plane, when needed (this

693-526: A much more compact instrument, one which can sometimes be successfully mounted on the Cassegrain focus. Since inexpensive and adequately stable computer-controlled alt-az telescope mounts were developed in the 1980s, the Nasmyth design has generally supplanted the coudé focus for large telescopes. For instruments requiring very high stability, or that are very large and cumbersome, it is desirable to mount

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756-529: A nearly flat focal plane if the primary and secondary curvature are properly figured , making it well suited for wide field and photographic observations. Almost every professional reflector telescope in the world is of the Ritchey–Chrétien design. Including a third curved mirror allows correction of the remaining distortion, astigmatism, from the Ritchey–Chrétien design. This allows much larger fields of view. The Dall–Kirkham Cassegrain telescope's design

819-411: A night. The Katzman Automatic Imaging Telescope is a robotic telescope designed to look for supernova. The telescope uses 76 cm (30 inch) diameter mirror that feeds a CCD imager with 20 slot filter wheel. The telescope is also supported by an electronic weather station, that can feed data to the robotic telescope control system. Several computers run software that controls the telescope and take in

882-505: A primary and secondary concave mirror, with the same curvature, and the same tilt to the main axis. Most Yolos use toroidal reflectors . The Yolo design eliminates coma, but leaves significant astigmatism, which is reduced by deformation of the secondary mirror by some form of warping harness, or alternatively, polishing a toroidal figure into the secondary. Like Schiefspieglers, many Yolo variations have been pursued. The needed amount of toroidal shape can be transferred entirely or partially to

945-422: A rotating mirror consisting of a liquid metal in a tray that is spun at constant speed. As the tray spins, the liquid forms a paraboloidal surface of essentially unlimited size. This allows making very big telescope mirrors (over 6 metres), but they are limited to use by zenith telescopes . In a prime focus design no secondary optics are used, the image is accessed at the focal point of the primary mirror . At

1008-439: A solution. The telescope was aluminized in 1934, 1938, 1946, and 1951. Nicholas Mayall was a long time user of the Crossley and added a slitless spectrograph to extend its usefulness in the face of larger telescopes. NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley reflector. Other early photographic imaging targets, dating to 1899, include GC 4628 and GC 4964, GC 4373, and

1071-478: A ‘reflecting’ telescope in 1663. It would be ten years (1673), before the experimental scientist Robert Hooke was able to build this type of telescope, which became known as the Gregorian telescope . Five years after Gregory designed his telescope and five years before Hooke built the first such Gregorian telescope, Isaac Newton in 1668 built his own reflecting telescope , which is generally acknowledged as

1134-523: Is a 36-inch (910 mm) reflecting telescope located at Lick Observatory in the U.S. state of California . It was used between 1895 and 2010, and was donated to the observatory by Edward Crossley , its namesake. It was the largest glass reflecting telescope in the United States for several years after its recommissioning in California. Lick Director, James Edward Keeler , remarked of

1197-399: Is actually less than a classical Cassegrain. Because this is less noticeable at longer focal ratios , Dall–Kirkhams are seldom faster than f/15. There are several designs that try to avoid obstructing the incoming light by eliminating the secondary or moving any secondary element off the primary mirror's optical axis , commonly called off-axis optical systems . The Herschelian reflector

1260-412: Is always some compromise in a reflecting telescope's optical design. Because the primary mirror focuses light to a common point in front of its own reflecting surface almost all reflecting telescope designs have a secondary mirror , film holder, or detector near that focal point partially obstructing the light from reaching the primary mirror. Not only does this cause some reduction in the amount of light

1323-474: Is composed of a solid glass cylinder whose front surface has been ground to a spherical or parabolic shape. A thin layer of aluminum is vacuum deposited onto the mirror, forming a highly reflective first surface mirror . Some telescopes use primary mirrors which are made differently. Molten glass is rotated to make its surface paraboloidal, and is kept rotating while it cools and solidifies. (See Rotating furnace .) The resulting mirror shape approximates

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1386-559: Is named after William Herschel , who used this design to build very large telescopes including the 40-foot telescope in 1789. In the Herschelian reflector the primary mirror is tilted so the observer's head does not block the incoming light. Although this introduces geometrical aberrations, Herschel employed this design to avoid the use of a Newtonian secondary mirror since the speculum metal mirrors of that time tarnished quickly and could only achieve 60% reflectivity. A variant of

1449-408: Is one of the simplest and least expensive designs for a given size of primary, and is popular with amateur telescope makers as a home-build project. The Cassegrain telescope (sometimes called the "Classic Cassegrain") was first published in a 1672 design attributed to Laurent Cassegrain . It has a parabolic primary mirror, and a hyperbolic secondary mirror that reflects the light back down through

1512-453: Is placed just to the side of the light entering the telescope, and positioned afocally so as to send parallel light on to the tertiary. The concave tertiary mirror is positioned exactly twice as far to the side of the entering beam as was the convex secondary, and its own radius of curvature distant from the secondary. Because the tertiary mirror receives parallel light from the secondary, it forms an image at its focus. The focal plane lies within

1575-480: Is the case of the catadioptric Schiefspiegler ). One variation of a multi-schiefspiegler uses a concave primary, convex secondary and a parabolic tertiary. One of the interesting aspects of some Schiefspieglers is that one of the mirrors can be involved in the light path twice — each light path reflects along a different meridional path. Stevick-Paul telescopes are off-axis versions of Paul 3-mirror systems with an added flat diagonal mirror. A convex secondary mirror

1638-451: Is the reflector telescope's basic optical element that creates an image at the focal plane. The distance from the mirror to the focal plane is called the focal length . Film or a digital sensor may be located here to record the image, or a secondary mirror may be added to modify the optical characteristics and/or redirect the light to film, digital sensors, or an eyepiece for visual observation. The primary mirror in most modern telescopes

1701-492: The Giant Magellan Telescope . The Newtonian telescope was the first successful reflecting telescope, completed by Isaac Newton in 1668. It usually has a paraboloid primary mirror but at focal ratios of about f/10 or longer a spherical primary mirror can be sufficient for high visual resolution. A flat secondary mirror reflects the light to a focal plane at the side of the top of the telescope tube. It

1764-507: The Schmidt camera , which use both a spherical mirror and a lens (called a corrector plate) as primary optical elements, mainly used for wide-field imaging without spherical aberration. The late 20th century has seen the development of adaptive optics and lucky imaging to overcome the problems of seeing , and reflecting telescopes are ubiquitous on space telescopes and many types of spacecraft imaging devices. A curved primary mirror

1827-435: 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

1890-527: The " Ring nebula in Lyra ." Keeler notes that in a 4-hour exposure, 16 new nebulae were found, seeing objects that were normally much to hard to make out with the reflector visually. 1899: As an example of its performance, Keeler noted that in a two-hour exposure of the "cluster in Hercules" made on July 13, 1899, he could count 5400 stars on the photograph. Keeler noted how with long exposure on this telescope

1953-424: The "swarms of minute stars" that gave it a nebulous look were resolved. In 1900, Assistant Astronomer Charles Dillon Perrine took hundreds of photographs of the near-Earth asteroid 433 Eros for the determination of the solar parallax . From 1902 to 1905, after significant reconstruction by Perrine, he discovered eight comets and the sixth and seventh satellites (moons) of Jupiter. 1940: Mayall's Object

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2016-489: The Cassegrain, the Schiefspiegler telescope ("skewed" or "oblique reflector") uses tilted mirrors to avoid the secondary mirror casting a shadow on the primary. However, while eliminating diffraction patterns this leads to an increase in coma and astigmatism. These defects become manageable at large focal ratios — most Schiefspieglers use f/15 or longer, which tends to restrict useful observations to objects which fit in

2079-549: The Crossley in 1900, "... by far the most effective instrument in the Observatory for certain class of astronomical work." Given to the Lick Observatory in 1895 by British politician Edward Crossley , it was rebuilt from the ground up as it was on a very flimsy mounting. It was last used in 2010 in the search for extra-solar planets but has been taken out of service due to budget cuts. The mirror, and some of

2142-435: The advances in reflecting telescopes included the perfection of parabolic mirror fabrication in the 18th century, silver coated glass mirrors in the 19th century (built by Léon Foucault in 1858), long-lasting aluminum coatings in the 20th century, segmented mirrors to allow larger diameters, and active optics to compensate for gravitational deformation. A mid-20th century innovation was catadioptric telescopes such as

2205-547: The data from the sensors. The telescope's development was funded by the NSF at private donors since 1989, turning 30-inch (~760 mm) telescope in a computer controlled super nova huntress. The telescope can also monitor the brightness of variable stars . KAIT discovered its first supernova in 1997, SN 1997bs. The next year (1998) twenty supernova were found after improvements to the telescope, and in 1999 forty supernova were discovered. The telescope has been noted for discovering

2268-613: The edge of that same field of view they suffer from off axis aberrations: There are reflecting telescope designs that use modified mirror surfaces (such as the Ritchey–Chrétien telescope ) or some form of correcting lens (such as catadioptric telescopes ) that correct some of these aberrations. Nearly all large research-grade astronomical telescopes are reflectors. There are several reasons for this: The Gregorian telescope , described by Scottish astronomer and mathematician James Gregory in his 1663 book Optica Promota , employs

2331-490: The first reflecting telescope. It used a spherically ground metal primary mirror and a small diagonal mirror in an optical configuration that has come to be known as the Newtonian telescope . Despite the theoretical advantages of the reflector design, the difficulty of construction and the poor performance of the speculum metal mirrors being used at the time meant it took over 100 years for them to become popular. Many of

2394-404: The focal point is some type of structure for holding a film plate or electronic detector. In the past, in very large telescopes, an observer would sit inside the telescope in an "observing cage" to directly view the image or operate a camera. Nowadays CCD cameras allow for remote operation of the telescope from almost anywhere in the world. The space available at prime focus is severely limited by

2457-459: The image in a mechanically advantageous position. Since reflecting telescopes use mirrors , the design is sometimes referred to as a catoptric telescope . From the time of Newton to the 1800s, the mirror itself was made of metal – usually speculum metal . This type included Newton's first designs and the largest telescope of the 19th century, the Leviathan of Parsonstown with

2520-496: The initial mounts, came from the 36-inch reflector originally mounted in Andrew Ainslie Common 's backyard Ealing observatory. He had used it from 1879 to 1886 to prove the concept of long exposure astrophotography (recording objects too faint to be seen by the naked eye for the first time). Common sold it to Crossley who had it until 1895. The 36-inch A.A.Common mirror was made by George Calver for Common, and

2583-423: The instrument on a rigid structure, rather than moving it with the telescope. Whilst transmission of the full field of view would require a standard coudé focus, spectroscopy typically involves the measurement of only a few discrete objects, such as stars or galaxies. It is therefore feasible to collect light from these objects with optical fibers at the telescope, placing the instrument at an arbitrary distance from

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2646-550: The largest reflector on Earth. After a world war and national economic crisis the "Perrine telescope" at the Bosque Alegre astrophysical station ( Estación Astrofísica de Bosque Alegre ) was inaugurated in 1942 when it was the largest reflector in South America. In the 1930s, the Crossley mirror was tested with vapor-deposited aluminum for reflection, rather than coated by using a silver metal precipitated out of

2709-493: The metal mirrors only reflected about 2 ⁄ 3 of the light and the metal would tarnish . After multiple polishings and tarnishings, the mirror could lose its precise figuring needed. Reflecting telescopes became extraordinarily popular for astronomy and many famous telescopes, such as the Hubble Space Telescope , and popular amateur models use this design. In addition, the reflection telescope principle

2772-434: The mirror near its edge do not converge with those that reflect from nearer the center of the mirror, a defect called spherical aberration . To avoid this problem most reflecting telescopes use parabolic shaped mirrors , a shape that can focus all the light to a common focus. Parabolic mirrors work well with objects near the center of the image they produce, (light traveling parallel to the mirror's optical axis ), but towards

2835-453: The movement of the telescope in order to avoid collision with obstacles such as walls or equipment inside the observatory. The Nasmyth design is similar to the Cassegrain except the light is not directed through a hole in the primary mirror; instead, a third mirror reflects the light to the side of the telescope to allow for the mounting of heavy instruments. This is a very common design in large research telescopes. Adding further optics to

2898-403: The need to avoid obstructing the incoming light. Radio telescopes often have a prime focus design. The mirror is replaced by a metal surface for reflecting radio waves , and the observer is an antenna . For telescopes built to the Cassegrain design or other related designs, the image is formed behind the primary mirror, at the focal point of the secondary mirror . An observer views through

2961-414: The primary mirror. In large focal ratios optical assemblies, both primary and secondary mirror can be left spherical and a spectacle correcting lens is added between the secondary mirror and the focal plane ( catadioptric Yolo ). The addition of a convex, long focus tertiary mirror leads to Leonard's Solano configuration. The Solano telescope doesn't contain any toric surfaces. One design of telescope uses

3024-797: The principles of curved mirrors, discussed the idea of building a telescope using a mirror as the image forming objective. There were reports that the Bolognese Cesare Caravaggi had constructed one around 1626 and the Italian professor Niccolò Zucchi , in a later work, wrote that he had experimented with a concave bronze mirror in 1616, but said it did not produce a satisfactory image. The potential advantages of using parabolic mirrors , primarily reduction of spherical aberration with no chromatic aberration , led to many proposed designs for reflecting telescopes. The most notable being James Gregory , who published an innovative design for

3087-417: The public, as well as donated services. For example, the heavy parts of the telescope were shipped by The Southern Pacific Company at no cost, a service of over US$ 1,000 (at that time). Converting the buying power of 1896 dollars to 2017 dollars, that can be estimated at US$ 12,000. The reflecting telescope type was scarcely used in the United States at the time of the donation, with a noted exception being

3150-429: The rear of the telescope, or a camera or other instrument is mounted on the rear. Cassegrain focus is commonly used for amateur telescopes or smaller research telescopes. However, for large telescopes with correspondingly large instruments, an instrument at Cassegrain focus must move with the telescope as it slews; this places additional requirements on the strength of the instrument support structure, and potentially limits

3213-661: The same diameter as the telescope's primary mirror) and very long focal lengths. Such instruments could not withstand being moved, and adding mirrors to the light path to form a coudé train , diverting the light to a fixed position to such an instrument housed on or below the observing floor (and usually built as an unmoving integral part of the observatory building) was the only option. The 60-inch Hale telescope (1.5 m), Hooker Telescope , 200-inch Hale Telescope , Shane Telescope , and Harlan J. Smith Telescope all were built with coudé foci instrumentation. The development of echelle spectrometers allowed high-resolution spectroscopy with

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3276-477: The supernova 2013ej was discovered by KAIT in the galaxy Messier 74 ; it was noted for being as bright as 10th magnitude. In 2014, KAIT helped determine the age of a supernova found in the galaxy M83 , because it had images of that region of the sky from just a few days prior to its discovery, establishing it had not brightened at that time. In 2016, KAIT spotted the super nova SN 2016coj in NGC 4125 , thought to be

3339-576: The supernova SN 1999em. This super nova was in the spiral galaxy NGC 1637 , and was observed later by telescope such as the VLT (4x8.2m). Another example of KAIT discovery was SN 1999ec , a type Ib supernova that was discovered in the interacting galaxy NGC 2207 on October 2, 1999. In 2011, KAIT was one of six telescopes used for the Lick AGN Monitoring Project. Between 1998 and 2013, KAIT had discovered 900 supernova. In 2013,

3402-423: The system collects, it also causes a loss in contrast in the image due to diffraction effects of the obstruction as well as diffraction spikes caused by most secondary support structures. The use of mirrors avoids chromatic aberration but they produce other types of aberrations . A simple spherical mirror cannot bring light from a distant object to a common focus since the reflection of light rays striking

3465-471: The system of mirrors, but is accessible to the eye with the inclusion of a flat diagonal. The Stevick-Paul configuration results in all optical aberrations totaling zero to the third-order, except for the Petzval surface which is gently curved. The Yolo was developed by Arthur S. Leonard in the mid-1960s. Like the Schiefspiegler, it is an unobstructed, tilted reflector telescope. The original Yolo consists of

3528-638: The telescope from 1902 to 1905. Perrine would use the rebuilt Crossley to great effect in discovering eight comets and the sixth and seventh satellites (moons) of Jupiter. The Crossley was so effective that when Perrine became the director of the Argentine National Observatory in Cordoba in 1909, he established a program to install a 60-inch (76-centimeter) reflecting telescope in Argentina. At that time it would have been equal to

3591-692: The telescope. Examples of fiber-fed spectrographs include the planet-hunting spectrographs HARPS or ESPRESSO . Additionally, the flexibility of optical fibers allow light to be collected from any focal plane; for example, the HARPS spectrograph utilises the Cassegrain focus of the ESO 3.6 m Telescope , whilst the Prime Focus Spectrograph is connected to the prime focus of the Subaru telescope . Crossley telescope The Crossley telescope

3654-555: The well-regarded Common 36-inch telescope. Holden and Crossley exchanged letters and worked out transferring the telescope. Crossley was very impressed by the enhanced observing conditions at Mount Hamilton , and, in April 1895, he formally telegraphed the Lick that he would donate the telescope. Funds had to be raised to ship the telescope to California, which included money from various donors including many small donations from members of

3717-496: The work of H. Draper 's reflector. Observations by Keeler helped establish large reflecting telescopes with metal-coated glass mirrors as astronomically useful, as opposed to earlier cast speculum metal mirrors. Great refractors were still in vogue, but the Crossley reflector foreshadowed the success of large reflectors in the 1900s. Other large reflectors followed, such as the Harvard 60-inch Reflector (152 cm), also with

3780-554: Was applied to other electromagnetic wavelengths, and for example, X-ray telescopes also use the reflection principle to make image-forming optics . The idea that curved mirrors behave like lenses dates back at least to Alhazen 's 11th century treatise on optics, works that had been widely disseminated in Latin translations in early modern Europe . Soon after the invention of the refracting telescope , Galileo , Giovanni Francesco Sagredo , and others, spurred on by their knowledge of

3843-529: Was created by Horace Dall in 1928 and took on the name in an article published in Scientific American in 1930 following discussion between amateur astronomer Allan Kirkham and Albert G. Ingalls, the magazine editor at the time. It uses a concave elliptical primary mirror and a convex spherical secondary. While this system is easier to grind than a classic Cassegrain or Ritchey–Chrétien system, it does not correct for off-axis coma. Field curvature

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3906-489: Was discovered by American astronomer Nicholas U. Mayall of the Lick Observatory on 13 March 1940, using the Crossley reflector. In 1990, the Crossley was used to test the photometric detection of exoplanets , including around the star CM Draconis . Comets known to have been photographed using the Crossley include: In 1978, the Crossley was used to observe planetary nebulae with photoelectric photometry ( spectrophotometry ). (100 cm equals 1 meter) *Note

3969-481: Was ordered after Common wanted one bigger than the 18-inch reflecting telescope, which also had a mirror from Calver. Common completed this telescope by 1879, and went on to make a 60-inch telescope; he sold the 36-inch to Crossley. Crossley set the telescope up in Halifax, England in a new dome. Meanwhile, at the Lick Observatory in California, Edward S. Holden , the director, learned that Crossley wanted to sell

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