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NGC 4939
NGC 4939 is a large spiral galaxy located in the constellation Virgo. It is located at a distance of about 120 million light years from Earth, which, given its apparent dimensions, means that NGC 4939 is about 190,000 light years across. It was discovered by William Herschel on March 25, 1786. Characteristics NGC 4939 has been characterised as a Seyfert galaxy, a galaxy category which features bright point-like nuclei. NGC 4939 is a type II Seyfert galaxy. Its X-ray spectrum is more consistent with a Compton-thick cold reflection source, which means that the source is hidden behind dense material, mainly gas and dust, and the X-rays observed have been reflected, but a Compton-thin transmission model could not be ruled out. The equivalent width of the FeKα line is large, indicating too that it is a Compton-thick source. Further observations by Swift Observatory confirmed its Compton-thick nature. The source of activity in the active galactic nuclei is a supermassive black hole ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
New General Catalogue
The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxy, galaxies, star clusters and emission nebulae. Dreyer published two supplements to the NGC in 1895 and 1908, known as the ''Index Catalogues'' (abbreviated IC), describing a further 5,386 astronomical objects. Thousands of these objects are best known by their NGC or IC numbers, which remain in widespread use. The NGC expanded and consolidated the cataloguing work of William Herschel, William and Caroline Herschel, and John Herschel's ''General Catalogue of Nebulae and Clusters of Stars''. Objects south of the Celestial sphere, celestial equator are catalogued somewhat less thoroughly, but many were included based on observation by John Herschel or James Dunlop. The NGC contained multiple errors, but attempts to eliminate them were made by the ''Revised New Ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equivalent Width
The equivalent width of a spectral line is a measure of the area of the line on a plot of intensity versus wavelength in relation to underlying continuum level. It is found by forming a rectangle with a height equal to that of continuum emission, and finding the width such that the area of the rectangle is equal to the area in the spectral line. It is a measure of the strength of spectral features that is primarily used in astronomy. Definition Formally, the equivalent width is given by the equation W_\lambda = \int d\lambda = \int (1 - F_s / F_c) d\lambda. Here, F_c(\lambda) represents the underlying continuum intensity, while F_s(\lambda) represents the intensity of the actual spectrum (the line and continuum). Then W_\lambda represents the width of a hypothetical line which drops to an intensity of zero and has the "same integrated flux deficit from the continuum as the true one." This equation can be applied to either emission or absorption, but when applied to emission, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zwicky Transient Facility
The Zwicky Transient Facility (ZTF, List of observatory codes, obs. code: IAU code#I41, I41) is a wide-field sky astronomical survey using a new camera attached to the Samuel Oschin Telescope at Palomar Observatory in San Diego County, California, United States. Commissioned in 2018, it supersedes the (Intermediate) Palomar Transient Factory (2009–2017) that used the same observatory code. It is named after the Swiss people, Swiss astronomer Fritz Zwicky. Description Observing in visible and infrared wavelengths, the Zwicky Transient Facility is designed to detect Transient astronomical event, transient objects that rapidly change in brightness, for example supernovae, gamma ray bursts, and collision between two neutron stars, and moving objects like comets and asteroids. The new camera is made of 16 Charge-coupled device, CCDs of 6144×6160 pixels each, enabling each exposure to cover an area of 47 square degrees. The Zwicky Transient Facility is designed to image the enti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lick Observatory
The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton (California), Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The observatory is managed by the University of California Observatories, with headquarters on the University of California, Santa Cruz campus, where its scientific staff moved in the mid-1960s. It is named after James Lick. The first new moon of Jupiter to be identified since the time of Galileo, Amalthea (moon), Amalthea, the planet's fifth moon, was discovered at this observatory in 1892. Early history Lick Observatory is the world's first permanently occupied mountain-top observatory. The observatory, in a Classical Revival architecture, Classical Revival style structure, was constructed between 1876 and 1887, from a bequest from James Lick of $700,000, . Lick, originally a carpenter and piano maker, had arrived from Peru in San Franc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type II Supernova
A Type II supernova or SNII (plural: ''supernovae'') results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun () to undergo this type of explosion. Type II supernovae are distinguished from other types of supernovae by the presence of hydrogen in their spectra. They are usually observed in the spiral arms of galaxies and in H II regions, but not in elliptical galaxies; those are generally composed of older, low-mass stars, with few of the young, very massive stars necessary to cause a supernova. Stars generate energy by the nuclear fusion of elements. Unlike the Sun, massive stars possess the mass needed to fuse elements that have an atomic mass greater than hydrogen and helium, albeit at increasingly higher temperatures and pressures, causing correspondingly shorter stellar life spans. The degeneracy pressure of electrons and the energy generated by th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Astronomical Union
The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and development through global cooperation. It was founded on 28 July 1919 in Brussels, Belgium and is based in Paris, France. The IAU is composed of individual members, who include both professional astronomers and junior scientists, and national members, such as professional associations, national societies, or academic institutions. Individual members are organised into divisions, committees, and working groups centered on particular subdisciplines, subjects, or initiatives. the Union had 85 national members and 12,734 individual members, spanning 90 countries and territories. Among the key activities of the IAU is serving as a forum for scientific conferences. It sponsors nine annual symposia and holds a triannual General Assembly that sets policy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paul Wild (Swiss Astronomer)
Paul Wild (; 5 October 1925 – 2 July 2014) was a Swiss astronomer and director of the Astronomical Institute of the University of Bern, who discovered numerous comets, asteroids and supernovae. Biography Wild was born on 5 October 1925 in the village of Wädenswil near Zürich, Switzerland. From 1944 through 1950, he studied mathematics and physics at the ETH Zurich. Thereafter, he worked at the California Institute of Technology where he researched galaxies and supernovas under the leadership of countryman Fritz Zwicky from 1951 through 1955. At the Zimmerwald Observatory, near Bern, Wild made his first cometary discovery C/1957 U1 (1957 IX) on 2 October 1957. The parabolic comet was later named "Latyshev-Wild– Burnham". Professor Wild became director of the Astronomical Institute of the University of Bern in 1980, and remained in this position until 1991. He died on 2 July 2014 at the age of 88 in Bern. Discoveries During countless nights Wild observed the ski ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the ''progenitor'', either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months. The last supernova directly observed in the Milky Way was Kepler's Supernova in 1604, appearing not long after Tycho's Supernova in 1572, both of which were visible to the naked eye. The supernova remnant, remnants of more recent supernovae have been found, and observations of supernovae in other galaxies suggest they occur in the Milky Way on average about three times every century. A supernova in the Milky Way would almost certainly be observable through mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rotational Speed
Rotational frequency, also known as rotational speed or rate of rotation (symbols ''ν'', lowercase Greek nu, and also ''n''), is the frequency of rotation of an object around an axis. Its SI unit is the reciprocal seconds (s−1); other common units of measurement include the hertz (Hz), cycles per second (cps), and revolutions per minute (rpm). Rotational frequency can be obtained dividing ''angular frequency'', ω, by a full turn (2 π radians): ''ν''ω/(2πrad). It can also be formulated as the instantaneous rate of change of the number of rotations, ''N'', with respect to time, ''t'': ''n''d''N''/d''t'' (as per International System of Quantities). (11 pages) Similar to ordinary period (physics), period ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grand Design Spiral Galaxy
A grand design spiral galaxy is a spiral galaxy with prominent and well-defined continuous spiral arms, as opposed to multi-arm, patchy and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy extend clearly around the galaxy, covering a significant portion of the galaxy's circumference. Theses spiral arms host lot of star formation making them home to an abundance of bright, hot and short lived massive stars. As of 2002, approximately 10 percent of all currently known spiral galaxies are classified as grand design type spirals, including M51 (Whirlpool Galaxy), M74 (Phantom Galaxy), M81 (Bode’s Galaxy), M83 (Southern pinwheel galaxy), M101 (Pinwheel Galaxy), NGC 6946 (Firworks Galaxy) and IC 342 (The Hidden Galaxy). Origin of structure Density wave theory is the preferred explanation for the well-defined structure of grand design spirals, first suggested by Chia-Chiao Lin and Frank Shu in 1964. The term "grand design" ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barred Spiral Galaxy
A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well. The Milky Way Galaxy, where the Solar System is located, is classified as a barred spiral galaxy. Edwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence and arranged them into sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb-type galaxies lie in between the two. SB0 is a barred lenticular galaxy. A new type, SBm, was subsequently created to describe somewhat Barred irregular galaxy, irregular barred spirals, such as the Magellanic Clouds, which were once classified as irregular galaxies, but have since been found t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
INTEGRAL
In mathematics, an integral is the continuous analog of a Summation, sum, which is used to calculate area, areas, volume, volumes, and their generalizations. Integration, the process of computing an integral, is one of the two fundamental operations of calculus,Integral calculus is a very well established mathematical discipline for which there are many sources. See and , for example. the other being Derivative, differentiation. Integration was initially used to solve problems in mathematics and physics, such as finding the area under a curve, or determining displacement from velocity. Usage of integration expanded to a wide variety of scientific fields thereafter. A definite integral computes the signed area of the region in the plane that is bounded by the Graph of a function, graph of a given Function (mathematics), function between two points in the real line. Conventionally, areas above the horizontal Coordinate axis, axis of the plane are positive while areas below are n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
