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NGC 4815
NGC 4815 is an open cluster in the constellation Musca. It was discovered by John Herschel in 1834. It is located approximately 10,000 light years away from Earth. Characteristics NGC 4815 is an intermediate age cluster. Carraro and Ortolani determined the age of the cluster to be 500 million years, based on BV photometry, which is nearly the same as the Hyades, while Sagar et al. determined its age at 400±50 million years and Kharchenko et al. at 400 million years. Friel at al. estimated its age to be between 500 and 630 million years. There are 69 probable member stars within the angular radius of the cluster and 39 within the central part of the cluster. Five blue stragglers have been detected in the cluster, and 15 red giants are probable members of the cluster. The earliest main sequence stars are of type A0. One of the stars in the cluster region shows extremely red colour along with blue ultraviolet colour and it could be an interacting binary star. The turnoff ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark Energy Spectroscopic Instrument
The Dark Energy Spectroscopic Instrument (DESI) is a scientific research instrument for conducting spectrographic astronomical surveys of distant galaxies. Its main components are a focal plane containing 5,000 fiber-positioning robots, and a bank of spectrographs which are fed by the fibers. The new instrument will enable an experiment to probe the expansion history of the universe and the mysterious physics of dark energy. The instrument is operated by the Lawrence Berkeley National Laboratory under funding from the US Department of Energy's Office of Science. Construction of the new instrument, now completed, was principally funded by the US Department of Energy's Office of Science, and by other numerous sources including the US National Science Foundation, the UK Science and Technology Facilities Council, France's Alternative Energies and Atomic Energy Commission, Mexico's National Council of Science and Technology, Spain's Ministry of Science and Innovation, by the Gordon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blue Straggler
A blue straggler is a main-sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hert ... star in an open cluster, open or globular cluster that is more luminosity, luminous and stellar classification, bluer than stars at the main sequence turnoff point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry (astronomy), photometry of the stars in the globular cluster Messier 3, M3. Standard theories of stellar evolution hold that the position of a star on the Hertzsprung–Russell diagram should be determined almost entirely by the initial mass of the star and its age. In a cluster, stars all formed at approximately the same time, and thus in an H–R diagram for a cluster, all stars should lie along a clearly defined curve set by the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Process
The alpha process, also known as the alpha ladder, is one of two classes of nuclear fusion reactions by which stars convert helium into heavier elements, the other being the triple-alpha process. The triple-alpha process consumes only helium, and produces carbon. After enough carbon has accumulated, further reactions below take place, listed below. Each step only consumes helium and the product of the previous reaction. :\begin \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \\ \ce& E=\mathsf \end The energy produced each the reaction, , is primarily in the gamma ray (), with a small amount taken by the byproduct element, as added momentum. It is a common misconception that the above sequence ends at \, _^\mathrm \, (or \, _^\mathrm \,, which is a decay product of \, _^\mathrm \,) because it is the most tightly bound nuclide - i.e., having the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metallicity
In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a convenient short term for ''"all elements except hydrogen and helium"''. This word-use is distinct from the conventional chemical or physical definition of a metal as an electrically conducting solid. Stars and nebulae with relatively high abundances of heavier elements are called "metal-rich" in astrophysical terms, even though many of those elements are nonmetals in chemistry. The presence of heavier elements hails from stellar nucleosynthesis, where the majority of elements heavier than hydrogen and helium in the Universe (''metals'', hereafter) are formed in the cores of stars as they evolve. Over time, stellar winds and supernovae deposit the metals into the surrounding environment, enriching the interstellar medium and providing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turnoff Point
The turnoff point for a star refers to the point on the Hertzsprung-Russell diagram where it leaves the main sequence after its main fuel is exhaustedthe main sequence turnoff. By plotting the turnoff points of individual stars in a star cluster one can estimate the cluster's age. Stars with no turnoff point Red dwarfs, also referred to as classM stars, are stars of 0.08–0.40 solar masses. They have sufficient mass to sustain hydrogen-to-helium fusion via the proton–proton chain reaction, but they do not have sufficient mass to create the temperatures and pressures necessary to fuse helium into carbon, nitrogen or oxygen (see CNO cycle). However, all their hydrogen is available for fusion, and low temperature and pressure means a lifetime measured in trillions of years. For example, the lifespan of a star of 0.1 solar masses is six trillion years. This lifespan greatly exceeds the current age of the universe, therefore all red dwarfs are main sequence stars. Even though extr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binary Star
A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in which case they are called ''visual binaries''. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy (''spectroscopic binaries'') or astrometry (''astrometric binaries''). If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called ''eclipsing binaries'', or, together with other binaries that change brightness as they orbit, ''photometric binaries''. If components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, thes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionization, ionize atoms, it can cause chemical reactions and causes many substances to glow or fluorescence, fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules. Short-wave ultraviolet light damages DNA and sterilizes surf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Main Sequence Star
Main may refer to: Geography * Main River (other) **Most commonly the Main (river) in Germany *Main, Iran, a village in Fars Province *"Spanish Main", the Caribbean coasts of mainland Spanish territories in the 16th and 17th centuries *''The Main'', the diverse core running through Montreal, Quebec, Canada, also separating the Two Solitudes *Main (lunar crater), located near the north pole of the Moon *Main (Martian crater) People and organisations * Main (surname), a list of people with this family name *Ma'in, alternate spelling for the Minaeans, an ancient people of modern-day Yemen *Main (band), a British ambient band formed in 1991 * Chas. T. Main, an American engineering and hydroelectric company founded in 1893 *MAIN (Mountain Area Information Network), former operator of WPVM-LP (MAIN-FM) in Asheville, North Carolina, U.S. Ships * ''Main'' (ship), an iron sailing ship launched in 1884 * SS ''Main'', list of steamships with this name * ''Main'' (A515), a modern ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Red Giant
A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or lower. The appearance of the red giant is from yellow-white to reddish-orange, including the spectral types K and M, sometimes G, but also class S stars and most carbon stars. Red giants vary in the way by which they generate energy: * most common red giants are stars on the red-giant branch (RGB) that are still fusing hydrogen into helium in a shell surrounding an inert helium core * red-clump stars in the cool half of the horizontal branch, fusing helium into carbon in their cores via the triple-alpha process * asymptotic-giant-branch (AGB) stars with a helium burning shell outside a degenerate carbon–oxygen core, and a hydrogen-burning shell just beyond that. Many of the well-known bright stars are red giants because they are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyades (star Cluster)
The Hyades (; Greek Ὑάδες, also known as Caldwell 41, Collinder 50, or Melotte 25) is the nearest open cluster and one of the best-studied star clusters. Located about away from the Sun, it consists of a roughly spherical group of hundreds of stars sharing the same age, place of origin, chemical characteristics, and motion through space.Bouvier J, Kendall T, Meeus G, Testi L, Moraux E, Stauffer JR, James D, Cuillandre J-C, Irwin J, McCaughrean MJ, Baraffe I, Bertin E. (2008) Brown dwarfs and very low mass stars in the Hyades cluster: a dynamically evolved mass function. ''Astronomy & Astrophysics'', 481: 661-672. Abstract at http://adsabs.harvard.edu/abs/2008A%26A...481..661B. From the perspective of observers on Earth, the Hyades Cluster appears in the constellation Taurus, where its brightest stars form a "V" shape along with the still-brighter Aldebaran. However, Aldebaran is unrelated to the Hyades, as it is located much closer to Earth and merely happens to lie alon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Open Cluster
An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and many more are thought to exist. They are loosely bound by mutual gravity, gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the Galactic Center. This can result in a migration to the main body of the galaxy and a loss of cluster members through internal close encounters. Open clusters generally survive for a few hundred million years, with the most massive ones surviving for a few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for longer. Open clusters have been found only in spiral galaxy, spiral and irregular galaxy, irregular galaxies, in which active star formation is o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photometry (astronomy)
Photometry, from Greek '' photo-'' ("light") and '' -metry'' ("measure"), is a technique used in astronomy that is concerned with measuring the flux or intensity of light radiated by astronomical objects. This light is measured through a telescope using a photometer, often made using electronic devices such as a CCD photometer or a photoelectric photometer that converts light into an electric current by the photoelectric effect. When calibrated against standard stars (or other light sources) of known intensity and colour, photometers can measure the brightness or apparent magnitude of celestial objects. The methods used to perform photometry depend on the wavelength region under study. At its most basic, photometry is conducted by gathering light and passing it through specialized photometric optical bandpass filters, and then capturing and recording the light energy with a photosensitive instrument. Standard sets of passbands (called a photometric system) are defined to allow a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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