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67-690: The Hale Telescope represented the technological limit in building large optical telescopes for over 30 years. It was the largest telescope in the world from its construction in 1949 until the Soviet BTA-6 was built in 1976, and the second largest until the construction of the Keck Observatory Keck 1 in Hawaii in 1993. Hale supervised the building of the telescopes at the Mount Wilson Observatory with grants from

134-641: A Serrurier truss , then newly invented by Mark U. Serrurier of Caltech in Pasadena in 1935, designed to flex in such a way as to keep all of the optics in alignment. Originally, the Hale Telescope was going to use a primary mirror of fused quartz manufactured by General Electric, but instead the primary mirror was cast in 1934 at Corning Glass Works in New York state using Corning's then new material called Pyrex ( borosilicate glass ). The mirror

201-417: A central hole was also part of the mold so light could pass through the finished mirror when it was used in a Cassegrain configuration (a Pyrex plug for this hole was also made to be used during the grinding and polishing process). While the glass was being poured into the mold during the first attempt to cast the 200-inch mirror, the intense heat caused several of the molding blocks to break loose and float to

268-406: A different mirror design to solve this problem, with either a single thin flexible mirror or a cluster of smaller segmented mirrors , whose shape is continuously adjusted by a computer-controlled active optics system using actuators built into the mirror support cell . The moving weight of the upper dome is about 1000 US tons, and can rotate on wheels. The dome doors weigh 125 tons each. The dome

335-477: A narrower range of observations. When the two mirrors are on one mount, the combined mirror spacing of the Large Binocular Telescope (22.8 m) allows fuller use of the aperture synthesis. Largest does not always equate to being the best telescopes, and overall light gathering power of the optical system can be a poor measure of a telescope's performance. Space-based telescopes , such as

402-487: A parallax for Polaris, but a distance inferred from it is 136.6 ± 0.5  pc (445.5 ly) for Polaris B, somewhat further than most previous estimates and several times more accurate. This was further improved to 137.2 ± 0.3  pc (447.6 ly), upon publication of the Gaia Data Release 3 catalog on 13 June 2022 which superseded Gaia Data Release 2. Polaris is depicted in the flag and coat of arms of

469-403: A pardon by saying, "I am as constant as the northern star/Of whose true-fixed and resting quality/There is no fellow in the firmament./The skies are painted with unnumbered sparks,/They are all fire and every one doth shine,/But there's but one in all doth hold his place;/So in the world" (III, i, 65–71). Of course, Polaris will not "constantly" remain as the north star due to precession , but this

536-787: A remarkable change and is on record as saying that "if they are real, these changes are 100 times larger than [those] predicted by current theories of stellar evolution ". In 2024, researchers led by Nancy Evans at the Harvard & Smithsonian , have studied with more accuracy the Polaris' smaller companion orbit using the CHARA Array . During this observation campaign they have succeeded in shooting Polaris features on its surface; large bright places and dark ones have appeared in close-up images, changing over time. Further, Polaris diameter size has been re-measured to 46  R ☉ , using

603-458: A single combined image are ranked by their equivalent aperture. Fixed altitude telescopes (e.g. HET) are also ranked by their equivalent aperture. All telescopes with an effective aperture of at least 3.00 metres (118 in) at visible or near-infrared wavelengths are included. (256 in) There are only a few sites capable of polishing the mirrors for these telescopes. SAGEM in France polished

670-500: A single rigid piece of glass. Using a monolithic mirror much larger than the 5-meter Hale or 6-meter BTA-6 is prohibitively expensive due to the cost of both the mirror, and the massive structure needed to support it. A mirror beyond that size would also sag slightly under its own weight as the telescope is rotated to different positions, changing the precision shape of the surface, which must be accurate to within 2 millionths of an inch (50 nm ). Modern telescopes over 9 meters use

737-457: A spectrograph to study spectra from 29 asteroids. In 2009, using a coronograph, the Hale Telescope was used to discover the star Alcor B , which is a companion to Alcor in the Big Dipper . In 2010, a new satellite of planet Jupiter was discovered with the 200-inch Hale, called S/2010 J 1 and later named Jupiter LI . In October 2017 the Hale Telescope was able to record the spectrum of

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804-541: Is a measure of the light-gathering power and resolution of a reflecting telescope . The mirrors themselves can be larger than the aperture, and some telescopes may use aperture synthesis through interferometry . Telescopes designed to be used as optical astronomical interferometers such as the Keck I and II used together as the Keck Interferometer (up to 85 m) can reach higher resolutions, although at

871-552: Is a triple star system , composed of the primary, a yellow supergiant designated Polaris Aa, in orbit with a smaller companion, Polaris Ab; the pair is in a wider orbit with Polaris B. The outer pair AB were discovered in August 1779 by William Herschel , where the 'A' refers to what is now known to be the Aa/Ab pair. Polaris Aa is an evolved yellow supergiant of spectral type F7Ib with 5.4 solar masses ( M ☉ ). It

938-495: Is changing rapidly due to the precession of Earth's axis , going from 2.5h in AD 2000 to 6h in AD 2100. Twice in each sidereal day Polaris's azimuth is true north; the rest of the time it is displaced eastward or westward, and the bearing must be corrected using tables or a rule of thumb . The best approximation is made using the leading edge of the " Big Dipper " asterism in the constellation Ursa Major. The leading edge (defined by

1005-548: Is commonly called the North Star or Pole Star . With an apparent magnitude that fluctuates around 1.98, it is the brightest star in the constellation and is readily visible to the naked eye at night. The position of the star lies less than 1° away from the north celestial pole , making it the current northern pole star . The stable position of the star in the Northern Sky makes it useful for navigation . As

1072-407: Is easier to obtain images when the planet is especially large (considerably larger than Jupiter ), widely separated from its parent star, and hot so that it emits intense infrared radiation. However, in 2010 a team from NASA 's Jet Propulsion Laboratory demonstrated that a vortex coronagraph could enable small scopes to directly image planets. The Hale had four times the light-collecting area of

1139-478: Is listed as one of the navigational stars . The modern name Polaris is shortened from Neo-Latin stella polaris " polar star ", coined in the Renaissance when the star had approached the celestial pole to within a few degrees. Gemma Frisius , writing in 1547, referred to it as stella illa quae polaris dicitur ("that star which is called 'polar'"), placing it 3° 8' from the celestial pole. In 2016,

1206-515: Is made of welded steel plates about 10 mm thick. The first observation of the Hale Telescope was of NGC 2261 on January 26, 1949. During its first 50 years, the Hale Telescope made many significant contributions to stellar evolution, cosmology, and high-energy astrophysics. Similarly, the telescope, and the technology developed for it, advanced the study of the spectra of stars, interstellar matter, AGNs, and quasars. Quasars were first identified as high redshift sources by spectra taken with

1273-495: Is only noticeable over centuries. In Inuit astronomy , Polaris is known as Nuutuittuq ( syllabics : ᓅᑐᐃᑦᑐᖅ ). In traditional Lakota star knowledge, Polaris is named "Wičháȟpi Owáŋžila". This translates to "The Star that Sits Still". This name comes from a Lakota story in which he married Tȟapȟúŋ Šá Wíŋ, "Red Cheeked Woman". However, she fell from the heavens, and in his grief Wičháȟpi Owáŋžila stared down from "waŋkátu" (the above land) forever. The Plains Cree call

1340-471: Is the closest Cepheid variable to Earth so its physical parameters are of critical importance to the whole astronomical distance scale . It is also the only one with a dynamically measured mass. The Hipparcos spacecraft used stellar parallax to take measurements from 1989 and 1993 with the accuracy of 0.97  milliarcseconds (970 microarcseconds), and it obtained accurate measurements for stellar distances up to 1,000 pc away. The Hipparcos data

1407-419: Is the first classical Cepheid to have a mass determined from its orbit. The two smaller companions are Polaris B, a 1.39  M ☉ F3 main-sequence star orbiting at a distance of 2,400  astronomical units (AU), and Polaris Ab (or P), a very close F6 main-sequence star with a mass of 1.26  M ☉ . Polaris B can be resolved with a modest telescope. William Herschel discovered

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1474-483: Is variable and unpredictable. The erratic changes of temperature and the amplitude of temperature changes during each cycle, from less than 50  K to at least 170 K, may be related to the orbit with Polaris Ab. Research reported in Science suggests that Polaris is 2.5 times brighter today than when Ptolemy observed it, changing from third to second magnitude. Astronomer Edward Guinan considers this to be

1541-426: The 91st century . The celestial pole was close to Thuban around 2750 BC, and during classical antiquity it was slightly closer to Kochab (β UMi) than to Polaris, although still about 10 ° from either star. It was about the same angular distance from β UMi as to α UMi by the end of late antiquity . The Greek navigator Pytheas in ca. 320 BC described the celestial pole as devoid of stars. However, as one of

1608-542: The Carnegie Institution of Washington : the 60-inch (1.5 m) telescope in 1908 and the 100-inch (2.5 m) telescope in 1917. These telescopes were very successful, leading to the rapid advance in understanding of the scale of the Universe through the 1920s, and demonstrating to visionaries like Hale the need for even larger collectors. The chief optical designer for Hale's previous 100-inch telescope

1675-651: The Gaia distance of 446 ± 1 light-years, and its mass was determined at 5.13  M ☉ . Because Polaris lies nearly in a direct line with the Earth's rotational axis "above" the North Pole —the north celestial pole—Polaris stands almost motionless in the sky, and all the stars of the northern sky appear to rotate around it. Therefore, it makes an excellent fixed point from which to draw measurements for celestial navigation and for astrometry . The elevation of

1742-721: The Hubble Space Telescope , take advantage of being above the Earth's atmosphere to reach higher resolution and greater light gathering through longer exposure times. Location in the northern or southern hemisphere of the Earth can also limit what part of the sky can be observed, and climate conditions at the observatory site affect how often the telescope can be used each year. The combination of large mirrors, locations selected for stable atmosphere and favorable climate conditions, and  active optics and adaptive optics to correct for much of atmospheric turbulence allow

1809-538: The International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Polaris for the star α Ursae Minoris Aa. In antiquity, Polaris was not yet the closest naked-eye star to the celestial pole, and

1876-805: The Old English rune poem , the T-rune is apparently associated with "a circumpolar constellation", or the planet Mars. In the Hindu Puranas , it became personified under the name Dhruva ("immovable, fixed"). In the later medieval period, it became associated with the Marian title of Stella Maris "Star of the Sea" (so in Bartholomaeus Anglicus , c. 1270s), due to an earlier transcription error. An older English name, attested since

1943-651: The University of California , and the Jet Propulsion Laboratory . It is equipped with modern optical and infrared array imagers, spectrographs, and an adaptive optics system. It has also used lucky cam imaging, which in combination with adaptive optics pushed the mirror close to its theoretical resolution for certain types of viewing. One of the Corning Labs' glass test blanks for the Hale

2010-577: The "circle described by the pole star about the pole". In Shakespeare's play Julius Caesar , written around 1599, Caesar describes himself as being "as constant as the northern star", though in Caesar's time there was no constant northern star. Despite its relative brightness, it is not, as is popularly believed, the brightest star in the sky. Polaris was referenced in Nathaniel Bowditch 's 1802 book, American Practical Navigator , where it

2077-532: The 14th century, is lodestar "guiding star", cognate with the Old Norse leiðarstjarna , Middle High German leitsterne . The ancient name of the constellation Ursa Minor, Cynosura (from the Greek κυνόσουρα "the dog's tail"), became associated with the pole star in particular by the early modern period. An explicit identification of Mary as stella maris with the polar star ( Stella Polaris ), as well as

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2144-463: The Cepheid instability strip , but it may be due to interference between the primary and the first- overtone pulsation modes. Authors disagree on whether Polaris is a fundamental or first-overtone pulsator and on whether it is crossing the instability strip for the first time or not. The temperature of Polaris varies by only a small amount during its pulsations, but the amount of this variation

2211-521: The Hale Telescope. Halley's Comet (1P) upcoming 1986 approach to the Sun was first detected by astronomers David C. Jewitt and G. Edward Danielson on 16 October 1982 using the 200-inch Hale Telescope equipped with a CCD camera . Two moons of the planet Uranus were discovered in September 1997, bringing the planet's total known moons to 17 at that time. One was Caliban (S/1997 U 1), which

2278-461: The Polaris A system, with an eccentricity of 0.64. K. W. Kamper in 1996 produced refined elements with a period of 29.59 ± 0.02 years and an eccentricity of 0.608 ± 0.005 . In 2019, a study by R. I. Anderson gave a period of 29.32 ± 0.11 years with an eccentricity of 0.620 ± 0.008 . There were once thought to be two more widely separated components—Polaris C and Polaris D—but these have been shown not to be physically associated with

2345-436: The Polaris system. Polaris Aa, the supergiant primary component, is a low-amplitude Population I classical Cepheid variable , although it was once thought to be a type II Cepheid due to its high galactic latitude . Cepheids constitute an important standard candle for determining distance, so Polaris, as the closest such star, is heavily studied. The variability of Polaris had been suspected since 1852; this variation

2412-418: The amplitude is now increasing again, a reversal not seen in any other Cepheid. The period, roughly 4 days, has also changed over time. It has steadily increased by around 4.5 seconds per year except for a hiatus in 1963–1965. This was originally thought to be due to secular redward (a long term change in redshift that causes light to stretch into longer wavelengths, causing it to appear red) evolution across

2479-471: The best site, and less likely to be affected by the growing light pollution problem in urban centers like Los Angeles . The Corning Glass Works was assigned the task of making a 200-inch (5.1 m) primary mirror. Construction of the observatory facilities and dome started in 1936, but because of interruptions caused by World War II , the telescope was not completed until 1948 when it was dedicated. Due to slight distortions of images, corrections were made to

2546-531: The brighter stars close to the celestial pole, Polaris was used for navigation at least from late antiquity, and described as ἀεί φανής ( aei phanēs ) "always visible" by Stobaeus (5th century), also termed Λύχνος ( Lychnos ) akin to a burner or lamp and would reasonably be described as stella polaris from about the High Middle Ages and onwards, both in Greek and Latin. On his first trans-Atlantic voyage in 1492, Christopher Columbus had to correct for

2613-567: The changes in velocity along the line of sight were due to a combination of the four-day pulsation period combined with a much longer orbital period and a large eccentricity of around 0.6. Moore published preliminary orbital elements of the system in 1929, giving an orbital period of about 29.7 years with an eccentricity of 0.63. This period was confirmed by proper motion studies performed by B. P. Gerasimovič in 1939. As part of her doctoral thesis, in 1955 E. Roemer used radial velocity data to derive an orbital period of 30.46 y for

2680-424: The closest Cepheid variable its distance is used as part of the cosmic distance ladder . The revised Hipparcos stellar parallax gives a distance to Polaris of about 433 light-years (133 parsecs ), while the successor mission Gaia gives a distance of about 448 light-years (137 parsecs ). Calculations by other methods vary widely. Although appearing to the naked eye as a single point of light, Polaris

2747-570: The distance. The next major step in high precision parallax measurements comes from Gaia , a space astrometry mission launched in 2013 and intended to measure stellar parallax to within 25 microarcseconds (μas). Although it was originally planned to limit Gaia's observations to stars fainter than magnitude 5.7, tests carried out during the commissioning phase indicated that Gaia could autonomously identify stars as bright as magnitude 3. When Gaia entered regular scientific operations in July 2014, it

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2814-428: The entire constellation of Ursa Minor was used for navigation rather than any single star. Polaris moved close enough to the pole to be the closest naked-eye star, even though still at a distance of several degrees, in the early medieval period, and numerous names referring to this characteristic as polar star have been in use since the medieval period. In Old English, it was known as scip-steorra ("ship-star") . In

2881-537: The first recognized interstellar object, 1I/2017 U1 ("ʻOumuamua"); while no specific mineral was identified it showed the visitor had a reddish surface color. In December 2023 the Hale Telescope began serving as the receiving antenna for the Deep Space Optical Communications experiment on NASA's Psyche mission . Up until the year 2010, telescopes could only directly image exoplanets under exceptional circumstances. Specifically, it

2948-616: The four VLT mirrors, the two Gemini mirrors, and the 36 segments for GTC. The Steward Observatory Mirror Lab cast and polished the two LBT mirrors, the two Magellan mirrors, the MMT replacement mirror, and the LSST primary/tertiary mirror. It is currently making the mirrors for the Giant Magellan Telescope. The Keck segments were made by Schott AG. The SALT and LAMOST segments were cast and polished by LZOS. The mirror for Subaru

3015-501: The largest Earth based telescopes to reach higher resolution than the Hubble Space Telescope. Another advantage of Earth based telescopes is the comparatively low cost of upgrading and replacing instruments. This list is ordered by optical aperture, which has historically been a useful gauge of limiting resolution, optical area, physical size, and cost. Multiple mirror telescopes that are on the same mount and can form

3082-465: The largest in the world at the time of their construction, by the same aperture criterion as above. These telescopes are under construction and will meet the list inclusion criteria once completed: Selected large telescopes which are in detailed design or pre-construction phases: Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor . It is designated α Ursae Minoris ( Latinized to Alpha Ursae Minoris ) and

3149-697: The last world-leading telescope to have a parabolic primary mirror . In 1928 Hale secured a grant of $ 6 million from the Rockefeller Foundation for "the construction of an observatory, including a 200-inch reflecting telescope" to be administered by the California Institute of Technology (Caltech), of which Hale was a founding member. In the early 1930s, Hale selected a site at 1,700 m (5,600 ft) on Palomar Mountain in San Diego County, California , US, as

3216-537: The optical shop in Pasadena (now the Synchrotron building at Caltech) standard telescope mirror making techniques were used to turn the flat blank into a precise concave parabolic shape, although they had to be executed on a grand scale. A special 240 in (6.1 m) 25,000 lb (11 t) mirror cell jig was constructed which could employ five different motions when the mirror was ground and polished. Over 13 years almost 10,000 lb (4.5 t) of glass

3283-716: The second-largest scope when it was commissioned in 1949. Other contemporary telescopes were the Hooker Telescope at the Mount Wilson Observatory and the Otto Struve Telescope at the McDonald Observatory. List of largest optical reflecting telescopes This list of the largest optical reflecting telescopes with objective diameters of 3.0 metres (120 in) or greater is sorted by aperture , which

3350-469: The star above the horizon gives the approximate latitude of the observer. In 2018 Polaris was 0.66° (39.6 arcminutes) away from the pole of rotation (1.4 times the Moon disc) and so revolves around the pole in a small circle 1.3° in diameter. It will be closest to the pole (about 0.45 degree, or 27 arcminutes) soon after the year 2100. Because it is so close to the celestial north pole, its right ascension

3417-528: The star in Nehiyawewin : acâhkos êkâ kâ-âhcît "the star that does not move" ( syllabics : ᐊᒑᐦᑯᐢ ᐁᑳ ᑳ ᐋᐦᒌᐟ ). In Mi'kmawi'simk the star is named Tatapn . In the ancient Finnish worldview, the North Star has also been called taivaannapa and naulatähti ("the nailstar") because it seems to be attached to the firmament or even to act as a fastener for the sky when other stars orbit it. Since

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3484-512: The star in August 1779 using a reflecting telescope of his own, one of the best telescopes of the time. In January 2006, NASA released images, from the Hubble telescope , that showed the three members of the Polaris ternary system. The variable radial velocity of Polaris A was reported by W. W. Campbell in 1899, which suggested this star is a binary system. Since Polaris A is a known cepheid variable, J. H. Moore in 1927 demonstrated that

3551-589: The starry sky seemed to rotate around it, the firmament is thought of as a wheel, with the star as the pivot on its axis. The names derived from it were sky pin and world pin . Many recent papers calculate the distance to Polaris at about 433 light-years (133 parsecs), based on parallax measurements from the Hipparcos astrometry satellite. Older distance estimates were often slightly less, and research based on high resolution spectral analysis suggests it may be up to 110 light years closer (323 ly/99 pc). Polaris

3618-428: The stars Dubhe and Merak ) is referenced to a clock face, and the true azimuth of Polaris worked out for different latitudes. The apparent motion of Polaris towards and, in the future, away from the celestial pole, is due to the precession of the equinoxes . The celestial pole will move away from α UMi after the 21st century, passing close by Gamma Cephei by about the 41st century , moving towards Deneb by about

3685-737: The telescope throughout 1949. It became available for research in 1950. Postage Stamp. The US Post Office issued a 3c postage stamp in 1948 commemorating the Hale Telescope and Observatory. A functioning one-tenth scale model of the telescope was also made at Corning. The 200-inch (510 cm) telescope saw first light on January 26, 1949, at 10:06   pm PST under the direction of American astronomer Edwin Powell Hubble , targeting NGC 2261 , an object also known as Hubble's Variable Nebula. The telescope continues to be used every clear night for scientific research by astronomers from Caltech and their operating partners, Cornell University ,

3752-426: The top, ruining the mirror. The defective mirror was used to test the annealing process. After the mold was re-engineered, a second mirror was successfully cast. After cooling several months, the finished mirror blank was transported by rail to Pasadena, California. Once in Pasadena the mirror was transferred from the rail flat car to a specially designed semi-trailer for road transport to where it would be polished. In

3819-566: The use of Cynosura as a name of the star, is evident in the title Cynosura seu Mariana Stella Polaris (i.e. "Cynosure, or the Marian Polar Star"), a collection of Marian poetry published by Nicolaus Lucensis (Niccolo Barsotti de Lucca) in 1655. Its name in traditional pre-Islamic Arab astronomy was al-Judayy الجدي ("the kid", in the sense of a juvenile goat ["le Chevreau"] in Description des Etoiles fixes), and that name

3886-458: Was George Willis Ritchey , who intended the new telescope to be of Ritchey–Chrétien design. Compared to the usual parabolic primary, this design would have provided sharper images over a larger usable field of view. However, Ritchey and Hale had a falling-out. With the project already late and over budget, Hale refused to adopt the new design, with its complex curvatures, and Ritchey left the project. The Mount Palomar Hale Telescope turned out to be

3953-694: Was cast by Corning and polished at Contraves Brashear Systems in Pennsylvania, USA. This table does not include all the largest mirrors manufactured. The Steward Observatory Mirror Lab produced the 6.5 metre f/1.25 collimator used in the Large Optical Test and Integration Site of Lockheed Martin , used for vacuum optical testing of other telescopes. Segmented mirrors are also referred to as mosaic mirrors. Single mirrors are also referred to monolithic mirrors, and can be sub-categorized in types, such as solid or honeycomb. These telescopes were

4020-424: Was cast in a mold with 36 raised mold blocks (similar in shape to a waffle iron ). This created a honeycomb mirror that cut the amount of Pyrex needed down from over 40 short tons (36 t) to just 20 short tons (18 t), making a mirror that would cool faster in use and have multiple "mounting points" on the back to evenly distribute its weight (note – see external links 1934 article for drawings). The shape of

4087-430: Was configured to routinely process stars in the magnitude range 3 – 20. Beyond that limit, special procedures are used to download raw scanning data for the remaining 230 stars brighter than magnitude 3; methods to reduce and analyse these data are being developed; and it is expected that there will be "complete sky coverage at the bright end" with standard errors of "a few dozen μas". Gaia Data Release 2 does not include

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4154-399: Was confirmed by Ejnar Hertzsprung in 1911. The range of brightness of Polaris is given as 1.86–2.13, but the amplitude has changed since discovery. Prior to 1963, the amplitude was over 0.1 magnitude and was very gradually decreasing. After 1966, it very rapidly decreased until it was less than 0.05 magnitude; since then, it has erratically varied near that range. It has been reported that

4221-408: Was discovered on 6 September 1997 by Brett J. Gladman , Philip D. Nicholson , Joseph A. Burns , and John J. Kavelaars using the 200-inch Hale Telescope. The other Uranian moon discovered then is Sycorax (initial designation S/1997 U 2) and was also discovered using the 200 inch Hale Telescope. The Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) survey used the Hale Telescope with

4288-434: Was examined again with more advanced error correction and statistical techniques. Despite the advantages of Hipparcos astrometry , the uncertainty in its Polaris data has been pointed out and some researchers have questioned the accuracy of Hipparcos when measuring binary Cepheids like Polaris. The Hipparcos reduction specifically for Polaris has been re-examined and reaffirmed but there is still not widespread agreement about

4355-423: Was ground and polished away, reducing the weight of the mirror to 14.5 short tons (13.2 t). The mirror was coated (and still is re-coated every 18–24 months) with a reflective aluminum surface using the same aluminum vacuum-deposition process invented in 1930 by Caltech physicist and astronomer John Strong . The Hale's 200 in (510 cm) mirror was near the technological limit of a primary mirror made of

4422-483: Was used for the C. Donald Shane telescope 's 120-inch (300 cm) primary mirror. The collecting area of the mirror is about 31,000 square inches (20 square meters). The Hale Telescope uses a special type of equatorial mount called a "horseshoe mount", a modified yoke mount that replaces the polar bearing with an open "horseshoe" structure that gives the telescope full access to the entire sky, including Polaris and stars near it. The optical tube assembly (OTA) uses

4489-529: Was used in medieval Islamic astronomy as well. In those times, it was not yet as close to the north celestial pole as it is now, and used to rotate around the pole. It was invoked as a symbol of steadfastness in poetry, as "steadfast star" by Spenser . Shakespeare 's sonnet 116 is an example of the symbolism of the north star as a guiding principle: "[Love] is the star to every wandering bark / Whose worth's unknown, although his height be taken." In Julius Caesar , he has Caesar explain his refusal to grant

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