Celestial coordinate system

In astronomy, a celestial coordinate system is a system for specifying positions of satellites, stars and other celestial objects. Coordinate systems can specify an object's position in three-dimensional space or plot its direction on a celestial sphere, if the object's distance is unknown or trivial; the coordinate systems are implemented in either rectangular coordinates. Spherical coordinates, projected on the celestial sphere, are analogous to the geographic coordinate system used on the surface of Earth; these differ in their choice of fundamental plane, which divides the celestial sphere into two equal hemispheres along a great circle. Rectangular coordinates, in appropriate units, are the cartesian equivalent of the spherical coordinates, with the same fundamental plane and primary direction; each coordinate system is named after its choice of fundamental plane. The following table lists the common coordinate systems in use by the astronomical community; the fundamental plane divides the celestial sphere into two equal hemispheres and defines the baseline for the latitudinal coordinates, similar to the equator in the geographic coordinate system.

The poles are located at ±90° from the fundamental plane. The primary direction is the starting point of the longitudinal coordinates; the origin is the zero distance point, the "center of the celestial sphere", although the definition of celestial sphere is ambiguous about the definition of its center point. The horizontal, or altitude-azimuth, system is based on the position of the observer on Earth, which revolves around its own axis once per sidereal day in relation to the star background; the positioning of a celestial object by the horizontal system varies with time, but is a useful coordinate system for locating and tracking objects for observers on Earth. It is based on the position of stars relative to an observer's ideal horizon; the equatorial coordinate system is centered at Earth's center, but fixed relative to the celestial poles and the March equinox. The coordinates are based on the location of stars relative to Earth's equator if it were projected out to an infinite distance.

The equatorial describes the sky as seen from the Solar System, modern star maps exclusively use equatorial coordinates. The equatorial system is the normal coordinate system for most professional and many amateur astronomers having an equatorial mount that follows the movement of the sky during the night. Celestial objects are found by adjusting the telescope's or other instrument's scales so that they match the equatorial coordinates of the selected object to observe. Popular choices of pole and equator are the older B1950 and the modern J2000 systems, but a pole and equator "of date" can be used, meaning one appropriate to the date under consideration, such as when a measurement of the position of a planet or spacecraft is made. There are subdivisions into "mean of date" coordinates, which average out or ignore nutation, "true of date," which include nutation; the fundamental plane is the plane of the Earth's orbit, called the ecliptic plane. There are two principal variants of the ecliptic coordinate system: geocentric ecliptic coordinates centered on the Earth and heliocentric ecliptic coordinates centered on the center of mass of the Solar System.

The geocentric ecliptic system was the principal coordinate system for ancient astronomy and is still useful for computing the apparent motions of the Sun and planets. The heliocentric ecliptic system describes the planets' orbital movement around the Sun, centers on the barycenter of the Solar System; the system is used for computing the positions of planets and other Solar System bodies, as well as defining their orbital elements. The galactic coordinate system uses the approximate plane of our galaxy as its fundamental plane; the Solar System is still the center of the coordinate system, the zero point is defined as the direction towards the galactic center. Galactic latitude resembles the elevation above the galactic plane and galactic longitude determines direction relative to the center of the galaxy; the supergalactic coordinate system corresponds to a fundamental plane that contains a higher than average number of local galaxies in the sky as seen from Earth. Conversions between the various coordinate systems are given.

See the notes before using these equations. Horizontal coordinates A, azimuth a, altitude Equatorial coordinates α, right ascension δ, declination h, hour angle Ecliptic coordinates λ, ecliptic longitude β, ecliptic latitude Galactic coordinates l, galactic longitude b, galactic latitude Miscellaneous λo, observer's longitude ϕo, observer's latitude ε, obliquity of the ecliptic θL, local sidereal time θG, Greenwich sidereal time h = θ L − α or h = θ G + λ o − α α = θ L − h or α = θ G + λ o − h The classical equations, derived from spherical trigonometry, for

Argentina–Bangladesh relations

Argentina–Bangladesh relations refer to the bilateral relations between Argentina and Bangladesh. Bangladesh opened a diplomatic mission in Argentina in the 1970s. In 2008, Ernesto Carlos Alvarez was appointed as Argentine Ambassador to Bangladesh. In 2011, former foreign secretary of Bangladesh Mohamed Mijarul Quayes paid an official visit to Buenos Aires. Bangladesh and Argentina have shown interest in expanding the bilateral economic activities between the two countries. Bangladeshi ships, ready made garments and ceramics have been identified as products with huge potential in the Argentinian market. There is a good demand in Argentina for Bangladeshi ceramics with FARR Ceramics being a major Bangladeshi ceramics exporter to Argentina. Exports of soybean oil from Argentina to Bangladesh are expanding. Argentina has shown interests to conduct Spanish-language course for Bangladeshi officials. Argentina intends to sign visa waiver agreement with Bangladesh


Amati is the last name of a family of Italian violin makers who lived at Cremona from about 1538 to 1740. Their importance is considered equal to those of the Bergonzi and Stradivari families. Today, violins created by Nicolò Amati are valued at around $600,000; because of their age and rarity, Amati instruments are kept in museum or private collections and are played in public. Andrea Amati designed and created the violin and cello known as the "violin family", he standardized the basic form, size and method of construction. Makers from nearby Brescia experimented, such as Gasparo da Salò, Micheli and Pellegrino, but it was Andrea Amati in Cremona, who gave the modern violin family their definitive profile; the first violin was ordered by Lorenzo de' Medici in 1555. His letter to Amati stated the instrument was to be "made of the highest quality materials like that of a lute, but simple to play". What became of this first violin is not known. A number of his instruments survived for some time, dating between 1538 and 1574.

The largest number these are from 1560, a set for an entire orchestra of 38 ordered by Catherine de Médicis the regent queen of France and bore hand painted royal French decorations in gold including the motto and coat of arms of her son Charles IX of France. Of these 38 instruments ordered, Amati created violins of two sizes, violas of two sizes and large-sized cellos, they were in use until only 14 of these instruments survived. His work is marked by selection of the finest materials, great elegance in execution, soft clear amber, soft translucent varnish, an in depth use of acoustic and geometrical principles in design. Andrea Amati was succeeded by his sons Antonio Girolamo Amati. "The Brothers Amati", as they were known, implemented far-reaching innovations in design, including the perfection of the shape of the f-holes. They are thought to have pioneered the modern alto format of viola, in contrast to older tenor violas, but the widespread belief that they were the first ones to do so is incorrect given that Gasparo da Salo made violas ranging from altos of 39 cm to tenors of 44.7 cm.

Nicolò Amati was the son of Girolamo Amati. He was the most eminent of the family, he improved the model adopted by the rest of the Amatis and produced instruments capable of yielding greater power of tone. His pattern was unusually small, but he made a wider model now known as the "Grand Amati", which have become his most sought-after violins. Of his pupils, the most famous were Antonio Stradivari and Andrea Guarneri, the first of the Guarneri family of violin makers; the last maker of the family was Nicolò's son, Girolamo Amati, known as Hieronymus II. He improved the arching of his father's instruments. Instruments in the UK include Andrea Amati violins from the set delivered to Charles IX of France in 1564. Amati instruments at the Ashmolean Museum, Oxford. Andrea Amati Violin, 1564 Viola Amati instruments at the Royal Academy of Music Museum, London Amati instrument at the Tullie House Museum and Art Gallery, Carlisle Andrea Amati Violin, 1564 Amati instruments at the National Music Museum: Andrea Amati: "The King", circa 1545, the world's oldest extant cello Viola, 1560 Violin, 1560 Violin, 1574 Girolamo Amati: Double bass, 1680 Violin, 1604 Violin, 7/8-size, 1609 Violino piccolo, 1613 Nicolò Amati: Violin, 1628 Amati instruments at the Metropolitan Museum of Art Andrea Amati: Violin, c. 1560 Nicolò Amati: Violin, 1669 Patrick O'Brian's fictional British sea captain Jack Aubrey is described as owning a "fiddle far above his station, an Amati no less", in The Surgeon's Mate.

In the Wine-Dark Sea, book fifteen of the series, Stephen Maturin now has a Girolamo Amati and Aubrey a Guarneri. In Satyajit Ray's short story Bosepukure Khoonkharapi, the fictional detective Feluda deduces that a character was murdered because he owned an Amati violin. In the manga and anime series Gunslinger Girl, Henrietta carries an Amati violin case, it contains a Fabrique Nationale P90. On the radio show, Yours Truly, Johnny Dollar, the January 1956 episode "The Ricardo Amerigo Matter" centered on a stolen Amati violin. Antonio Stradivari Amati Quartet Dom Nicolò Amati, Italian luthier not part of this family but who adopted this surname Luthier San Maurizio, Venice Dilworth, John, "The Violin and Bow-Origins and Development" in: The Cambridge Companion to the Violin, ed. Robin Stowell. Cambridge: Cambridge University Press, pp. 1–29. Andrea Amati: Violin, Heilbrunn Timeline of Art History, The Metropolitan Museum of Art Instruments of the Amati family on the online database MIMO, website