A refracting telescope is a type of optical telescope that uses a lens as its objective to form an image. The refracting telescope design was used in spy glasses and astronomical telescopes but is used for long focus camera lenses. Although large refracting telescopes were popular in the second half of the 19th century, for most research purposes the refracting telescope has been superseded by the reflecting telescope which allows larger apertures. A refractor's magnification is calculated by dividing the focal length of the objective lens by that of the eyepiece. Refractors were the earliest type of optical telescope; the first practical refracting telescopes appeared in the Netherlands about 1608, were credited to three individuals, Hans Lippershey and Zacharias Janssen, spectacle-makers in Middelburg, Jacob Metius of Alkmaar. Galileo Galilei, happening to be in Venice in about the month of May 1609, heard of the invention and constructed a version of his own. Galileo communicated the details of his invention to the public, presented the instrument itself to the Doge Leonardo Donato, sitting in full council.
All refracting telescopes use the same principles. The combination of an objective lens 1 and some type of eyepiece 2 is used to gather more light than the human eye is able to collect on its own, focus it 5, present the viewer with a brighter and magnified virtual image 6; the objective in a refracting telescope bends light. This refraction causes parallel light rays to converge at a focal point; the telescope converts a bundle of parallel rays to make an angle α, with the optical axis to a second parallel bundle with angle β. The ratio β/α is called the angular magnification, it equals the ratio between the retinal image sizes obtained without the telescope. Refracting telescopes can come in many different configurations to correct for image orientation and types of aberration; because the image was formed by the bending of light, or refraction, these telescopes are called refracting telescopes or refractors. The design Galileo Galilei used in 1609 is called a Galilean telescope, it used a divergent eyepiece lens.
A Galilean telescope, because the design has no intermediary focus, results in a non-inverted and upright image. Galileo's best telescope magnified objects about 30 times; because of flaws in its design, such as the shape of the lens and the narrow field of view, the images were blurry and distorted. Despite these flaws, the telescope was still good enough for Galileo to explore the sky; the Galilean telescope could view the phases of Venus, was able to see craters on the Moon and four moons orbiting Jupiter. Parallel rays of light from a distant object would be brought to a focus in the focal plane of the objective lens; the eyepiece lens renders them parallel once more. Non-parallel rays of light from the object traveling at an angle α1 to the optical axis travel at a larger angle after they passed through the eyepiece; this leads to an increase in the apparent angular size and is responsible for the perceived magnification. The final image is a virtual image, is the same way up as the object.
The Keplerian telescope, invented by Johannes Kepler in 1611, is an improvement on Galileo's design. It uses a convex lens as the eyepiece instead of Galileo's concave one; the advantage of this arrangement is that the rays of light emerging from the eyepiece are converging. This allows for a much wider field of view and greater eye relief, but the image for the viewer is inverted. Higher magnifications can be reached with this design, but to overcome aberrations the simple objective lens needs to have a high f-ratio; the design allows for use of a micrometer at the focal plane. The achromatic refracting lens was invented in 1733 by an English barrister named Chester Moore Hall, although it was independently invented and patented by John Dollond around 1758; the design overcame the need for long focal lengths in refracting telescopes by using an objective made of two pieces of glass with different dispersion,'crown' and'flint glass', to limit the effects of chromatic and spherical aberration.
Each side of each piece is ground and polished, the two pieces are assembled together. Achromatic lenses are corrected to bring two wavelengths into focus in the same plane; the era of the'great refractors' in the 19th century saw large achromatic lenses culminating with the largest achromatic refractor built, the Great Paris Exhibition Telescope of 1900. Apochromatic refractors have objectives built with extra-low dispersion materials, they are designed to bring three wavelengths into focus in the same plane. The residual color error can be up than that of an achromatic lens; such telescopes contain elements of fluorite or special, extra-low dispersion glass in the objective and produce a crisp image, free of chromatic aberration. Due to the special materials needed in the fabrication, apochromatic refractors are more expensive than telescopes of other types with a comparable aperture. Refractors suffer from residual spherical aberration; this affects shorter focal ratios more than longer ones.
Astronomical seeing refers to the amount of apparent blurring and twinkling of astronomical objects like stars due to turbulent mixing in the atmosphere of Earth, causing variations of the optical refractive index. The seeing conditions on a given night at a given location describe how much Earth's atmosphere perturbs the images of stars as seen through a telescope; the most common seeing measurement is the full width at half maximum of the optical intensity across the seeing disc. The FWHM of the point spread function is the best possible angular resolution that can be achieved by an optical telescope in a long-exposure image, corresponds to the FWHM of the fuzzy blob seen when observing a point-like source through the atmosphere; the size of the seeing disc is determined by the seeing conditions at the time of the observation. The best conditions give a seeing disk diameter of ~0.4 arcseconds and are found at high-altitude observatories on small islands such as Mauna Kea or La Palma. Seeing is one of the biggest problems for Earth-based astronomy.
While large telescopes have theoretically milli-arcsecond resolution, the real image is limited to the average seeing disc during the observation. This can mean a factor of 100 between the potential and practical resolution. Starting in the 1990s, new adaptive optics have been introduced that can help correct for these effects improving the resolution of ground-based telescopes. Astronomical seeing has several effects: It causes the images of point sources, which in the absence of atmospheric turbulence would be steady Airy patterns produced by diffraction, to break up into speckle patterns, which change rapidly with time Long exposure images of these changing speckle patterns result in a blurred image of the point source, called a seeing disc The brightness of stars appears to fluctuate in a process known as scintillation or twinkling Atmospheric seeing causes the fringes in an astronomical interferometer to move The distribution of atmospheric seeing through the atmosphere causes the image quality in adaptive optics systems to degrade the further you look from the location of reference starThe effects of atmospheric seeing were indirectly responsible for the belief that there were canals on Mars.
In viewing a bright object such as Mars a still patch of air will come in front of the planet, resulting in a brief moment of clarity. Before the use of charge-coupled devices, there was no way of recording the image of the planet in the brief moment other than having the observer remember the image and draw it later; this had the effect of having the image of the planet be dependent on the observer's memory and preconceptions which led the belief that Mars had linear features. The effects of atmospheric seeing are qualitatively similar throughout the visible and near infra-red wavebands. At large telescopes the long exposure image resolution is slightly higher at longer wavelengths, the timescale for the changes in the dancing speckle patterns is lower. There are three common descriptions of the astronomical seeing conditions at an observatory: The full width at half maximum of the seeing disc r0 and t0 The CN2 profileThese are described in the sub-sections below: Without an atmosphere, a small star would have an apparent size, an "Airy disk", in a telescope image determined by diffraction and would be inversely proportional to the diameter of the telescope.
However, when light enters the Earth's atmosphere, the different temperature layers and different wind speeds distort the light waves, leading to distortions in the image of a star. The effects of the atmosphere can be modeled as rotating cells of air moving turbulently. At most observatories, the turbulence is only significant on scales larger than r0 and this limits the resolution of telescopes to be about the same as given by a space-based 10–20 cm telescope; the distortion changes at a high rate more than 100 times a second. In a typical astronomical image of a star with an exposure time of seconds or minutes, the different distortions average out as a filled disc called the point spread function or "seeing disc"; the diameter of the seeing disk, most defined as the full width at half maximum, is a measure of the astronomical seeing conditions. It follows from this definition that seeing is always a variable quantity, different from place to place, from night to night, variable on a scale of minutes.
Astronomers talk about "good" nights with a low average seeing disc diameter, "bad" nights where the seeing diameter was so high that all observations were worthless. The FWHM of the seeing disc is measured in arcseconds, abbreviated with the symbol. A 1.0″ seeing is a good one for average astronomical sites. The seeing of an urban environment is much worse. Good seeing nights tend to be clear, cold nights without wind gusts. Warm air rises, degrading the seeing, clouds. At the best high-altitude mountaintop observatories, the wind brings in stable air which has not been in contact with the ground, sometimes providing seeing as good as 0.4". The astronomical seeing conditions at an observatory can be conveniently described by the parameters r0 and t0. F
An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geophysical and volcanology are examples of disciplines for which observatories have been constructed. Observatories were as simple as containing an astronomical sextant or Stonehenge. Astronomical observatories are divided into four categories: space-based, ground-based, underground-based. Ground-based observatories, located on the surface of Earth, are used to make observations in the radio and visible light portions of the electromagnetic spectrum. Most optical telescopes are housed within a dome or similar structure, to protect the delicate instruments from the elements. Telescope domes have a slit or other opening in the roof that can be opened during observing, closed when the telescope is not in use. In most cases, the entire upper portion of the telescope dome can be rotated to allow the instrument to observe different sections of the night sky. Radio telescopes do not have domes.
For optical telescopes, most ground-based observatories are located far from major centers of population, to avoid the effects of light pollution. The ideal locations for modern observatories are sites that have dark skies, a large percentage of clear nights per year, dry air, are at high elevations. At high elevations, the Earth's atmosphere is thinner, thereby minimizing the effects of atmospheric turbulence and resulting in better astronomical "seeing". Sites that meet the above criteria for modern observatories include the southwestern United States, Canary Islands, the Andes, high mountains in Mexico such as Sierra Negra. A newly emerging site which should be added to this list is Mount Gargash. With an elevation of 3600 m above sea level, it is the home to the Iranian National Observatory and its 3.4m INO340 telescope. Major optical observatories include Mauna Kea Observatory and Kitt Peak National Observatory in the US, Roque de los Muchachos Observatory and Calar Alto Observatory in Spain, Paranal Observatory in Chile.
Specific research study performed in 2009 shows that the best possible location for ground-based observatory on Earth is Ridge A — a place in the central part of Eastern Antarctica. This location provides the least atmospheric disturbances and best visibility. Beginning in 1930s, radio telescopes have been built for use in the field of radio astronomy to observe the Universe in the radio portion of the electromagnetic spectrum; such an instrument, or collection of instruments, with supporting facilities such as control centres, visitor housing, data reduction centers, and/or maintenance facilities are called radio observatories. Radio observatories are located far from major population centers to avoid electromagnetic interference from radio, TV, other EMI emitting devices, but unlike optical observatories, radio observatories can be placed in valleys for further EMI shielding; some of the world's major radio observatories include the Socorro, in New Mexico, United States, Jodrell Bank in the UK, Arecibo in Puerto Rico, Parkes in New South Wales and Chajnantor in Chile.
Since the mid-20th century, a number of astronomical observatories have been constructed at high altitudes, above 4,000–5,000 m. The largest and most notable of these is the Mauna Kea Observatory, located near the summit of a 4,205 m volcano in Hawaiʻi; the Chacaltaya Astrophysical Observatory in Bolivia, at 5,230 m, was the world's highest permanent astronomical observatory from the time of its construction during the 1940s until 2009. It has now been surpassed by the new University of Tokyo Atacama Observatory, an optical-infrared telescope on a remote 5,640 m mountaintop in the Atacama Desert of Chile; the oldest proto-observatories, in the sense of a private observation post, Wurdi Youang, Australia Zorats Karer, Armenia Loughcrew, Ireland Newgrange, Ireland Stonehenge, Great Britain Quito Astronomical Observatory, located 12 minutes south of the Equator in Quito, Ecuador. Chankillo, Peru El Caracol, Mexico Abu Simbel, Egypt Kokino, Republic of Macedonia Observatory at Rhodes, Greece Goseck circle, Germany Ujjain, India Arkaim, Russia Cheomseongdae, South Korea Angkor Wat, CambodiaThe oldest true observatories, in the sense of a specialized research institute, include: 825 AD: Al-Shammisiyyah observatory, Iraq 869: Mahodayapuram Observatory, India 1259: Maragheh observatory, Iran 1276: Gaocheng Astronomical Observatory, China 1420: Ulugh Beg Observatory, Uzbekistan 1442: Beijing Ancient Observatory, China 1577: Constantinople Observatory of Taqi ad-Din, Turkey 1580: Uraniborg, Denmark 1581: Stjerneborg, Denmark 1642: Panzano Observatory, Italy 1642: Round Tower, Denmark 1633: Leiden Observatory, Netherlands 1667: Paris Observatory, France 1675: Royal Greenwich Observatory, England 1695: Sukharev Tower, Russia 1711: Berlin Observatory, Germany 1724: Jantar Mantar, India 1753: Stockholm Observatory, Sweden 1753: Vilnius University Observatory, Lithuania 1753: Navy Royal Institute and Observatory, Spain 1759: Trieste Observatory, Italy 1757: Macfarlane Observatory, Scotland 1759: Turin Observatory, Italy 1764: Brera Astronomical Observatory, Italy 1765: Mohr Observatory, Indonesia 1774: Vatican Observatory, Vatican 1785: Dunsink Observatory, Ireland 1786: Madras Observatory, India 1789: Armagh Observatory, Northern Ireland 1790: Real Observatorio de Madrid, Spain, 1803: National Astronomical Observatory, Bogotá, Colombia.
1811: Tartu Old Observatory, Estonia 1812: Astronomical Observatory of Capodimonte, Italy 1830/1842: Depot of Charts & Instruments
Max Planck Institute for Astronomy
For named astronomy institutes, see: Institute of Astronomy. The Max-Planck-Institut für Astronomie is a research institute of the Max Planck Society, it is located in Heidelberg, Baden-Württemberg, Germany near the top of the Koenigstuhl, adjacent to the historic Landessternwarte Heidelberg-Königstuhl astronomical observatory. The institute was founded in 1967, its founding directors were H. Elsässer, G. Munch, followed by S. V. W. Beckwith; the current directors are Thomas Henning. G. H. Herbig, Karl-Heinz Böhm, Immo Appenzeller, Willy Benz, Rafael Rebolo have been external scientific members. Current research interests include formation of planets, stars in the group of Thomas Henning and galaxies and cosmology in the group of Hans-Walter Rix; the MPIA builds instruments or parts of them for ground-based telescopes and satellites, including the following: Calar Alto Observatory, jointly run by the MPIA and the Instituto de Astrofísica de Andalucía Paranal Observatory Large Binocular Telescope Herschel Space Observatory The International Max Planck Research School for Astronomy and Cosmic Physics is a graduate program offering a PhD in astrophysics.
The school is run in cooperation with the University of Heidelberg. HIP 13044 b Homepage of the Max Planck Institute for Astronomy Homepage of the International Max Planck Research School for Astronomy and Cosmic Physics
Integrated Authority File
The Integrated Authority File or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used for documentation in libraries and also by archives and museums; the GND is managed by the German National Library in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero licence; the GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, an approach to unambiguous identification of single elements. It comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format; the Integrated Authority File became operational in April 2012 and integrates the content of the following authority files, which have since been discontinued: Name Authority File Corporate Bodies Authority File Subject Headings Authority File Uniform Title File of the Deutsches Musikarchiv At the time of its introduction on 5 April 2012, the GND held 9,493,860 files, including 2,650,000 personalised names.
There are seven main types of GND entities: LIBRIS Virtual International Authority File Information pages about the GND from the German National Library Search via OGND Bereitstellung des ersten GND-Grundbestandes DNB, 19 April 2012 From Authority Control to Linked Authority Data Presentation given by Reinhold Heuvelmann to the ALA MARC Formats Interest Group, June 2012
Karlsruhe is the second-largest city of the German federal state of Baden-Württemberg after its capital of Stuttgart, its 309,999 inhabitants make it the 21st largest city of Germany. On the right bank of the Rhine, the city lies near the French-German border, between the Mannheim/Ludwigshafen conurbation to the north, the Strasbourg/Kehl conurbation to the south, it is the largest city of a region named after Hohenbaden Castle in the city of Baden-Baden. Karlsruhe is the largest city in the South Franconian dialect area, the only other larger city in that area being Heilbronn; the city is the seat of the Federal Constitutional Court, as well as of the Federal Court of Justice and the Public Prosecutor General of the Federal Court of Justice. Karlsruhe was the capital of the Margraviate of Baden-Durlach, the Margraviate of Baden, the Electorate of Baden, the Grand Duchy of Baden, the Republic of Baden, its most remarkable building is Karlsruhe Palace, built in 1715. There are nine institutions of higher education in the city, most notably the Karlsruhe Institute of Technology.
Karlsruhe/Baden-Baden Airport is the second-busiest airport of Baden-Württemberg after Stuttgart Airport, the 17th-busiest airport of Germany. Karlsruhe lies to the east of the Rhine, completely on the Upper Rhine Plain, it contains the Turmberg in the east, lies on the borders of the Kraichgau leading to the Northern Black Forest. The Rhine, one of the world's most important shipping routes, forms the western limits of the city, beyond which lie the towns of Maximiliansau and Wörth am Rhein in the German state of Rhineland-Palatinate; the city centre is about 7.5 km from the river. Two tributaries of the Rhine, the Alb and the Pfinz, flow through the city from the Kraichgau to join the Rhine; the city lies at an altitude between 100 and 322 m. Its geographical coordinates are 49°00′N 8°24′E, its course is marked by a stone and painted line in the Stadtgarten. The total area of the city is 173.46 km2, hence it is the 30th largest city in Germany measured by land area. The longest north-south distance is 19.3 km in the east-west direction.
Karlsruhe is part of the urban area of Karlsruhe/Pforzheim, to which certain other towns in the district of Karlsruhe such as Bruchsal, Ettlingen and Rheinstetten, as well as the city of Pforzheim, belong. The city was planned with the palace tower at the center and 32 streets radiating out from it like the spokes of a wheel, or the ribs of a folding fan, so that one nickname for Karlsruhe in German is the "fan city". All of these streets survive to this day; because of this city layout, in metric geometry, Karlsruhe metric refers to a measure of distance that assumes travel is only possible along radial streets and along circular avenues around the centre. The city centre is the oldest part of town and lies south of the palace in the quadrant defined by nine of the radial streets; the central part of the palace runs east-west, with two wings, each at a 45° angle, directed southeast and southwest. The market square lies on the street running south from the palace to Ettlingen; the market square has the town hall to the west, the main Lutheran church to the east, the tomb of Margrave Charles III William in a pyramid in the buildings, resulting in Karlsruhe being one of only three large cities in Germany where buildings are laid out in the neoclassical style.
The area north of the palace is a forest. The area to the east of the palace consisted of gardens and forests, some of which remain, but the Karlsruhe Institute of Technology, Wildparkstadion football stadium, residential areas have been built there; the area west of the palace is now residential. Karlsruhe experiences an oceanic climate and its winter climate is milder, compared to most other German cities, except for the Rhine-Ruhr area. Summers are hotter than elsewhere in the country and it is one of the sunniest cities in Germany, like the Rhine-Palatinate area. Precipitation is evenly spread throughout the year. In 2008, the weather station in Karlsruhe, operating since 1876, was closed. According to legend, the name Karlsruhe, which translates as "Charles’ repose" or "Charles' peace", was given to the new city after a hunting trip when Margrave Charles III William of Baden-Durlach, woke from a dream in which he dreamt of founding his new city. A variation of this story claims. Charles William founded the city on June 17, 1715, after a dispute with the citizens of his previous capital, Durlach.
The founding of the city is linked to the construction of the palace. Karlsruhe became the capital of Baden-Durlach, in 1771, of the united Baden until 1945. Built in 18
Asteroids are minor planets of the inner Solar System. Larger asteroids have been called planetoids; these terms have been applied to any astronomical object orbiting the Sun that did not resemble a planet-like disc and was not observed to have characteristics of an active comet such as a tail. As minor planets in the outer Solar System were discovered they were found to have volatile-rich surfaces similar to comets; as a result, they were distinguished from objects found in the main asteroid belt. In this article, the term "asteroid" refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There exist millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun's solar nebula that never grew large enough to become planets; the vast majority of known asteroids orbit within the main asteroid belt located between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects.
Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C-type, M-type, S-type. These were named after and are identified with carbon-rich and silicate compositions, respectively; the sizes of asteroids varies greatly. Asteroids are differentiated from meteoroids. In the case of comets, the difference is one of composition: while asteroids are composed of mineral and rock, comets are composed of dust and ice. Furthermore, asteroids formed closer to the sun; the difference between asteroids and meteoroids is one of size: meteoroids have a diameter of one meter or less, whereas asteroids have a diameter of greater than one meter. Meteoroids can be composed of either cometary or asteroidal materials. Only one asteroid, 4 Vesta, which has a reflective surface, is visible to the naked eye, this only in dark skies when it is favorably positioned. Small asteroids passing close to Earth may be visible to the naked eye for a short time; as of October 2017, the Minor Planet Center had data on 745,000 objects in the inner and outer Solar System, of which 504,000 had enough information to be given numbered designations.
The United Nations declared 30 June as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, Russian Federation, on 30 June 1908. In April 2018, the B612 Foundation reported "It's 100 percent certain we'll be hit, but we're not 100 percent sure when." In 2018, physicist Stephen Hawking, in his final book Brief Answers to the Big Questions, considered an asteroid collision to be the biggest threat to the planet. In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare. According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched; the first asteroid to be discovered, was considered to be a new planet.
This was followed by the discovery of other similar bodies, with the equipment of the time, appeared to be points of light, like stars, showing little or no planetary disc, though distinguishable from stars due to their apparent motions. This prompted the astronomer Sir William Herschel to propose the term "asteroid", coined in Greek as ἀστεροειδής, or asteroeidēs, meaning'star-like, star-shaped', derived from the Ancient Greek ἀστήρ astēr'star, planet'. In the early second half of the nineteenth century, the terms "asteroid" and "planet" were still used interchangeably. Overview of discovery timeline: 10 by 1849 1 Ceres, 1801 2 Pallas – 1802 3 Juno – 1804 4 Vesta – 1807 5 Astraea – 1845 in 1846, planet Neptune was discovered 6 Hebe – July 1847 7 Iris – August 1847 8 Flora – October 1847 9 Metis – 25 April 1848 10 Hygiea – 12 April 1849 tenth asteroid discovered 100 asteroids by 1868 1,000 by 1921 10,000 by 1989 100,000 by 2005 ~700,000 by 2015 Asteroid discovery methods have improved over the past two centuries.
In the last years of the 18th century, Baron Franz Xaver von Zach organized a group of 24 astronomers to search the sky for the missing planet predicted at about 2.8 AU from the Sun by the Titius-Bode law because of the discovery, by Sir William Herschel in 1781, of the planet Uranus at the distance predicted by the law. This task required that hand-drawn sky charts be prepared for all stars in the zodiacal band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would be spotted; the expected motion of the missing planet was about 30 seconds of arc per hour discernible by observers. The first object, was not discovered by a member of the group, but rather by accident in 1801 by Giuseppe Piazzi, director of the observatory of Palermo in Sicily, he discovered a new star-like object in Taurus and followed the displacement of this object during several nights. That year, Carl Friedrich Gauss used these observations to calculate the orbit of this unknown object, found to be between the planets Mars and Jupiter.
Piazzi named it after Ceres, the Roman goddess of agriculture. Three other asteroids (2 Pallas, 3 Juno, 4 Ves