Sun, river, United States
Sun, river, c.130 mi (210 km) long, rising in the Rocky Mts., NW Mont., and flowing generally E to the Missouri River at Great Falls. The Sun River project of the U.S. Bureau of Reclamation utilizes the Sun and its tributaries to irrigate c.92,000 acres (37,230 hectares) of land. Of the system of dams and reservoirs, Gibson Dam is one of the project's largest.sun, in astronomy
sun, intensely hot, self-luminous body of gases at the center of the solar system solar system, the sun and the surrounding planets, natural satellites , dwarf planets, asteroids, meteoroids, and comets that are bound by its gravity. The sun is by far the most massive part of the solar system, containing almost 99.9% of the system's total mass...... Click the link for more information. . Its gravitational attraction maintains the planets, comets, and other bodies of the solar system in their orbits.
General Characteristics of the Sun
The sun is actually a star of about medium size; it appears larger than the other stars because of its relative nearness to the earth. The earth's distance from the sun varies from 91,377,000 mi (147,053,000 km) at perihelion to 94,537,000 mi (152,138,000 km) at aphelion (see apsis apsis (pl. apsides), point in the orbit of a body where the body is neither approaching nor receding from another body about which it revolves. Any elliptical orbit has two apsides.
..... Click the link for more information. ). The mean distance is c.92,960,000 mi (149,591,000 km); this is taken as the astronomical unit astronomical unit (AU), mean distance between the earth and sun; one AU is c.92,960,000 mi (149,604,970 km). The astronomical unit is the principal unit of measurement within the solar system, e.g., Mercury is just over 1-3 AU and Pluto is about 39 AU from the sun.
..... Click the link for more information. (AU) of distance used for measuring distances within the solar system. The sun is approximately 865,400 mi (1,392,000 km) in diameter, and its volume is about 1,300,000 times that of the earth. Its mass is almost 700 times the total mass of all the bodies in the solar system and 332,000 times that of the earth. The sun's surface gravity is almost 28 times that of the earth; i.e., a body on the surface of the sun would weigh about 28 times its weight on earth. The density of the material composing the sun is about one fourth that of the earth; compared with water, the sun's average density is 1.41. At its center, the sun has a density of over 100 times that of water, a temperature of 10 to 20 million degrees Celsius, and a pressure of over 1 billion atmospheres.
Observations of sunspots and studies of the solar spectrum indicate that the sun rotates on its axis from east to west; because of its gaseous nature its rate of rotation varies somewhat with latitude, the speed being greatest (a period of almost 25 days) in the equatorial region and least at the poles (a period of about 35 days). The axis of the sun is inclined at an angle of about 7° to the plane of the ecliptic ecliptic (ēklĭp`tĭk, ĭ–)
..... Click the link for more information. .
The bright surface of the sun is called the photosphere photosphere, luminous, apparently opaque layer of gases that forms the visible surface of the sun or any other star. The photosphere lies between the dense interior gases and the more attenuated gases of the chromosphere .
..... Click the link for more information. . Its temperature is about 6,000°C;. The photosphere appears darker near the edge (limb) of the sun's disk because of greater absorption of light by the sun's atmosphere in this area; this phenomenon is called limb darkening. During an eclipse of the sun the chromosphere chromosphere (krō`məsfēr') [Gr.
..... Click the link for more information. and the corona corona, luminous envelope surrounding the sun , outside the chromosphere. Its density is less than one billionth that of the earth's atmosphere. The corona is visible only at the time of totality during a total eclipse of the sun.
..... Click the link for more information. (the outer layers of the sun's atmosphere) are observed. Also of interest is the high-speed, tenuous extension of the corona known as the solar wind solar wind, stream of ionized hydrogen—protons and electrons—with an 8% component of helium ions and trace amounts of heavier ions that radiates outward from the sun at high speeds.
..... Click the link for more information. .
Production of Solar Energy
The vast and continual production of solar energy cannot be attributed merely to combustion, to the gradual cooling of a hot body, to the fall of meteorites into the sun, or to gradual shrinkage with transformation of potential energy into heat (a theory proposed by Helmholtz). The theory of relativity with its implication of the equivalence of mass and energy led to the assumption that energy stored in the atoms constituting the sun's gases is constantly being released by conversion of some of the masses of the atom's nuclei during nuclear transmutations (see nuclear energy nuclear energy, the energy stored in the nucleus of an atom and released through fission, fusion, or radioactivity . In these processes a small amount of mass is converted to energy according to the relationship E = mc2, where E
..... Click the link for more information. ). H. A. Bethe proposed a cycle of nuclear reactions known as the carbon cycle, or CNO bi-cycle, to account for the nuclear changes. In this cycle carbon acts much as a catalyst, while hydrogen is transformed by a series of reactions into helium and large amounts of high-energy gamma radiation are released. It is now thought that the so-called proton-proton process is a more important energy source; this process begins with the collision of two protons and ends with the production of helium, while gamma radiation is released throughout.
See nucleosynthesis nucleosynthesis or nucleogenesis, in astronomy, production of all the chemical elements from the simplest element, hydrogen, by thermonuclear reactions within stars, supernovas, and in the big bang at the beginning of the universe (see nucleus ;
..... Click the link for more information. ; stellar evolution stellar evolution, life history of a star , beginning with its condensation out of the interstellar gas (see interstellar matter ) and ending, sometimes catastrophically, when the star has exhausted its nuclear fuel or can no longer adjust itself to a stable
..... Click the link for more information. .
The Study of the Sun
By means of the spectroscope spectrograph was developed. It was based on the same principle as the spectroscope, but it had a camera in place of the telescope. In recent years the electronic circuits built around the photomultiplier tube have replaced the camera, allowing real-time spectrographic analysis of
..... Click the link for more information. much has been learned about the composition of the sun. There are numerous dark lines of varying widths in the solar spectrum spectrum, arrangement or display of light or other form of radiation separated according to wavelength, frequency, energy, or some other property. Beams of charged particles can be separated into a spectrum according to mass in a mass spectrometer (see mass
..... Click the link for more information. . These were first intensively studied by Joseph Fraunhofer and are commonly known by his name. From a study of the lines the chemical composition of the sun is determined on the basis of the discovery by Kirchhoff that the dark lines correspond in position to the bright lines characteristic of the spectra produced by elements in the laboratory. The darkness of the lines in the sun's spectrum is attributed to the presence of a slightly cooler layer of gases above the photosphere, known as the reversing layer, which absorbs selectively the light of the photosphere and thus causes dark lines instead of bright ones to be observed through the spectroscope. By comparison of the sun's spectrum with laboratory spectra of incandescent elements, most of the elements known on earth have been identified in the sun's atmosphere.
Beyond the red portion of the visible solar spectrum is the infrared spectrum; for the study of these heat rays S. P. Langley invented the bolometer, a highly sensitive electrical device for measuring temperature. Solar heat and energy are measured by an instrument called the pyrheliometer. Other instruments devised especially for the study of the sun are the coronagraph and the spectroheliograph spectroheliograph, device for photographing the surface of the sun in a single wavelength of light, usually one corresponding to a chief element contained in the sun, e.g., hydrogen or calcium; the resulting photograph is called a spectroheliogram.
..... Click the link for more information. . These instruments have revealed a number of interesting phenomena occurring during the periods of solar activity associated with sunspots sunspots, dark, usually irregularly shaped spots on the sun's surface that are actually solar magnetic storms. The Chinese recorded dark features on the sun seen with the naked eye in 28 B.C.
..... Click the link for more information. , e.g., faculae, plages (flocculi), prominences, and flares.
Importance to Terrestrial Life
Without the heat and light of the sun, life as we know it could not exist on the earth. Since solar energy is used by green plants in the process of photosynthesis, the sun is the ultimate source of the energy stored both in food and fossil fuels. Solar heating sets up convection currents, and thus is the source of the energy of moving air. Falling rain also owes its energy to the sun because of the relation of solar radiation to the water cycle.
Bibliography
See K. Hufbauer, Exploring the Sun: Solar Science since Galileo (1993); R. Krippenhahn, Discovering the Secrets of the Sun (1994); K. J. H. Phillips, Guide to the Sun (1995); P. O. Taylor, Beginners Guide to the Sun (1996); S. T. Suess and B. T. Tsurutani, ed., From the Sun: Auroras, Magnetic Storms, Solar Flares, Cosmic Rays (1998).
Sun
Star around which the components of the solar system revolve. It is about five billion years old and is the dominant body of the system, with more than 99% of its mass. It converts five million tons of matter into energy every second by nuclear fusion reactions in its core, producing neutrinos (see solar neutrino problem) and solar radiation. The small amount of this energy that penetrates Earth’s atmosphere provides the light and heat that support life. A sphere of luminous gas 864,950 mi (1,392,000 km) in diameter, the Sun has about 330,000 times the mass of Earth. Its core temperature is close to 27 million °F (15 million °C) and its surface temperature about 10,000 °F (6,000 °C). The Sun, a spectral type G (yellow) star, has fairly average properties for a main-sequence star (see Hertzsprung-Russell diagram). It rotates at different rates at different latitudes; one rotation takes 36 days at the poles but only 25 days at the equator. The visible surface, or photosphere, is in constant motion, with the number and position of sunspots changing in a regular solar cycle. External phenomena include magnetic activity extending into the chromosphere and corona, solar flares, solar prominences, and the solar wind. Effects on Earth include auroras and disruption of radio communications and power-transmission lines. Despite its activity, the Sun appears to have remained relatively unchanged for billions of years. See also eclipse; heliopause.
Sun
(Sun Microsystems, Inc., Santa Clara, CA, www.sun.com) A major manufacturer of Unix-based workstations and servers. In 1981, Bavarian-born Andreas Bechtolsheim was licensing rights to a computer he designed. Named Sun for Stanford University Network and using off-the-shelf parts, it was an affordable workstation for engineers and scientists. In that year, he met Vinod Khosla, a native of India, who convinced him to form a company and expand. Khosla, Bechtolsheim and Scott McNealy, all Stanford MBAs, founded Sun in 1982.
Its first computers, the Sun-1 and subsequent Sun-2 were instant successes in the university market. Sun began to compete against its rival Apollo Computer, an east-coast workstation company, eventually surpassing it in sales (Apollo was later purchased by HP).
Sun has been a major force in open systems. Its computers have always run under Unix, which was licensed from AT&T and then later purchased outright. Sun and AT&T had formed such a tight alliance for a while that a host of Unix vendors formed the Open Software Foundation (OSF) in 1988 to keep Sun from dominating Unix.
In 1984, Bill Joy, head of R&D, designed NFS, which was broadly licensed and became the industry standard for file sharing. Sun later packaged its Unix components into a complete environment named Solaris, which it later ported to other platforms, including the Intel x86.
Sun used the Motorola 68K CPUs in its products until it designed its own RISC-based SPARC chips, which it launched with the SPARCstation 1 in 1989. Having gone through many iterations, SPARC CPUs are also made by Fujitsu and other third parties via licensing arrangements (see SPARC).
In the mid-1990s, Sun introduced the Java programming language and ushered in a new era for application development on the Internet (see Java and J2EE). Later on, Sun was a major proponent of network computers. See network computer and Sun-Netscape Alliance.
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| The Founders |
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| From left to right: Vinod Khosla, Bill Joy, Andreas Bechtolsheim and Scott McNealy. Although Joy was not a founder, he was hired shortly thereafter and became one of Sun's major contributors. (Image courtesy of Sun Microsystems, Inc.) |
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| The Sun-1 |
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| Sun's workstations were an instant success primarily in the university market. This led many professionals to the company who helped it grow steadily. (Image courtesy of Sun Microsystems, Inc.) |
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| The First SPARCstation |
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| In 1989, Sun introduced the SPARCstation 1, the first Sun computer that used the SPARC chip. (Image courtesy of Sun Microsystems, Inc.) |
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| Sun JavaStation |
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| Sun developed the Java programming language, and its network computer is aptly named. The JavaStation conforms to the NC Reference Profile and is available in several models. (Image courtesy of Sun Microsystems, Inc.) |
sun
www.solarviews.com/eng/sun.htm
www.michielb.nl/sun/kaft.htm
www.hao.ucar.edu/public/education/education.html
sun [sən]
Sun
| Sun - Sun Microsystems |
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