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Omega Nebula
The Omega Nebula is an H II region in the constellation Sagittarius. It was discovered by Philippe Loys de Chéseaux in 1745. Charles Messier catalogued it in 1764. It is by some of the richest starfields of the Milky Way, figuring in the northern two-thirds of Sagittarius. This feature is also known as the Swan Nebula, Checkmark Nebula, Lobster Nebula, and the Horseshoe Nebula, and catalogued as Messier 17 or M17 or NGC 6618. Characteristics The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years in diameter. The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter and has a mass of 30,000 solar masses. The total mass of the Omega Nebula is an estimated 800 solar masses. It is considered one of the brightest and most massive star-forming regions of our galaxy. Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.. The open cluster NGC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Very Large Telescope
The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with a primary mirror that measures in diameter. These optical telescopes, named ''Antu'', ''Kueyen'', ''Melipal'', and ''Yepun'' (all words for astronomical objects in the Mapuche language), are generally used separately but can be combined to achieve a very high angular resolution. The VLT array is also complemented by four movable Auxiliary Telescopes (ATs) with apertures. The VLT is capable of observing both visible and infrared wavelengths. Each individual telescope can detect objects that are roughly four billion times fainter than what can be seen with the naked eye. When all the telescopes are combined, the facility can achieve an angular resolution of approximately 0.002 arcsecond. In single telescope mode, the angular resol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. More precisely, the mass of the Sun is The solar mass is about times the mass of Earth (), or times the mass of Jupiter (). History of measurement The value of the gravitational constant was first derived from measurements that were made by Henry Cavendish in 1798 with a torsion balance. The value he obtained differs by only 1% from the modern value, but was not as precise. The diurnal parallax of the Sun was accurately measured during the transits of Venus in 1761 and 1769, yielding a value of (9 arcseconds, compared to the present value of ). From the value of the diurnal parallax, one can determine the distance to the Sun from the geometry of Earth. The first known estimate of the solar mass was by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carina–Sagittarius Arm
The Carina–Sagittarius Arm (also known as the Sagittarius Arm or Sagittarius–Carina Arm, labeled -I) is generally thought to be a minor spiral arm of the Milky Way galaxy. Each spiral arm is a long, diffuse curving streamer of stars that radiates from the Galactic Center. These gigantic structures are often composed of billions of stars and thousands of gas clouds. The Carina–Sagittarius Arm is one of the most pronounced arms in our galaxy as many HII regions, young stars and giant molecular clouds are concentrated in it. The Milky Way is a barred spiral galaxy, consisting of a central crossbar and bulge from which two major and several minor spiral arms radiate outwards. This arm lies between two major spiral arms, the Scutum–Centaurus Arm, the near part of which is visible looking ''inward'', i.e. toward the Galactic Center with the rest beyond the galactic central bulge, and the Perseus Arm, similar in size and shape but locally much closer looking outward, away from the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HD 168625
HD 168625 (V4030 Sagittarii) is a blue hypergiant star and candidate luminous blue variable located in the constellation of Sagittarius easy to see with amateur telescopes. It forms a visual pair with the also blue hypergiant (and luminous blue variable) HD 168607 and is located to the south-east of M17, the Omega Nebula. Distance The distance of HD 168625 and its association with the Omega Nebula and HD 168607 is in doubt; while some authors think both stars are physically associated and belong to the stellar association Serpens OB1, at a distance to the Sun of , or for both per Gaia Data Release 3 about , a 2002 study estimates this star is farther, at about and unrelated to the other two objects. Physical characteristics Assuming a distance of 2.2 kiloparsecs, the star would be 220,000 times brighter than the Sun, having a surface temperature of 12,000 K. At that distance it can be calculated to be losing mass through a fierce stellar wind at roughly per year ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypergiant
A hypergiant ( luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term ''hypergiant'' is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG ( red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia+, but red supergiants are rarely assigned these spectral classifications. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially star formation, stability, and their expected demise as supernovae. Notable examples of hypergiants include the Pistol Star, a blue hypergiant located close to the Galactic Center and one of the most luminous stars known; Rho Cassiopeiae, a yellow hypergiant that is one ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HD 168607
HD 168607 (V4029 Sagittarii) is a blue hypergiant and luminous blue variable (LBV) star located in the constellation of Sagittarius, easy to see with amateur telescopes. It forms a pair with HD 168625, also a blue hypergiant and possible luminous blue variable, that can be seen at the south-east of M17, the Omega Nebula. Physical properties HD 168607 was estimated to be about as far away as is the Omega Nebula (2.2 kiloparsecs, 7,200 light years, from the Sun) and no respective measurements have been found that discount physical association with HD 168625. Assuming this distance is correct, this star is 240,000 times brighter than the Sun with a surface temperature of . The Gaia Data Release 2 parallax of implies a closer distance of about . The apparent magnitude of this star or star system was observed to vary by 0.25 to 0.30 magnitudes with a period of 64 days when it was first identified as an α Cygni variable. Unlike its neighbour HD 168625, no n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luminous Blue Variable
Luminous blue variables (LBVs) are rare, massive, evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of the Large Magellanic Cloud. Discovery and history The LBV stars P Cygni and Eta Carinae, η Carinae have been known as unusual variables since the 17th century, but their true nature was not fully understood until late in the 20th century. In 1922 John Charles Duncan published the first three variable stars ever detected in an external galaxy, variables 1, 2, and 3, in the Triangulum Galaxy (M33). These were followed up by Edwin Hubble with three more in 1926: A, B, and C in M33. Then in 1929 Hubble added a list of variables detected in Messier 31, M31. Of these, Var A, Var B, Var C, and Var 2 in M33 and Var 19 in M31 were followed up with a detailed study by Hubble and Allan Sandage in 1953. Var 1 in M33 was excluded as being too faint a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Astrophysical Journal
''The Astrophysical Journal'' (''ApJ'') is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler. The journal discontinued its print edition and became an electronic-only journal in 2015. Since 1953, ''The Astrophysical Journal Supplement Series'' (''ApJS'') has been published in conjunction with ''The Astrophysical Journal'', with generally longer articles to supplement the material in the journal. It publishes six volumes per year, with two 280-page issues per volume. ''The Astrophysical Journal Letters'' (''ApJL''), established in 1967 by Subrahmanyan Chandrasekhar as Part 2 of ''The Astrophysical Journal'', is now a separate journal focusing on the rapid publication of high-impact astronomical research. The three journals were published by the University of Chicago Press for the American Astronomical Society until, in January 2009, publication was transferred to IOP Publis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
O-type Main-sequence Star
An O-type main-sequence star (O V) is a main-sequence (core hydrogen-burning) star of spectral type O and luminosity class V. These stars have between 15 and 90 times the mass of the Sun and surface temperatures between 30,000 and 50,000 K. They are between 40,000 and 1,000,000 times as luminous as the Sun. Spectral standard stars The "anchor" standards which define the MK classification grid for O-type main-sequence stars, i.e. those standards which have not changed since the early 20th century, are (O7 V) and (O9 V). The Morgan–Keenan–Kellerman (MKK) "Yerkes" atlas from 1943 listed O-type standards between O5 and O9, but only split luminosity classes for the O9s. The two MKK O9 V standards were Iota Orionis and . The revised Yerkes standards ("MK") presented listed in Johnson & Morgan (1953) presented no changes to the O5 to O8 types, and listed 5 O9 V standards (, , , , 10 Lacertae) and 3 O9.5 V standards (, Sigma Orionis, Zeta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectral Type
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The ''spectral class'' of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters ''O'', ''B'', ''A'', ''F'', ''G'', ''K'', and ''M'', a sequence from the hottest (''O'' type) to the coolest (''M'' type). Each letter class is then subdivided ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Young Star
A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of interstellar dust and gas. After the protostar blows away this envelope, it is optically visible, and appears on the stellar birthline in the Hertzsprung-Russell diagram. At this point, the star has acquired nearly all of its mass but has not yet started hydrogen burning (i.e. nuclear fusion of hydrogen). The star continues to contract, its internal temperature rising until it begins hydrogen burning on the zero age main sequence. This period of contraction is the pre-main sequence stage. An observed PMS object can either be a T Tauri star, if it has fewer than 2 solar masses (), or else a Herbig Ae/Be star, if it has 2 to 8 . Yet more massive stars have no pre-main-sequence stage because they contract too quickly as protostars. By t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and Gamma ray, gamma radiation (γ) * ''particle radiation'' consisting of particles of non-zero rest energy, such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation * ''acoustics, acoustic radiation'', such as ultrasound, sound, and seismic waves, all dependent on a physical transmission medium * ''gravitational radiation'', in the form of gravitational waves, ripples in spacetime Radiation is often categorized as either ''ionizing radiation, ionizing'' or ''non-ionizing radiation, non-ionizing'' depending on the energy of the radiated particles. Ionizing radiation carries more than 10 electron volt, electron volts (eV), which is enough to ionize atoms and molecul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
