118 résultats pour "astronomy"
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Astronomy - astronomy.
Telescopes may use either lenses or mirrors to gather visible light, permitting direct observation or photographic recording of distant objects. Those that use lenses arecalled refracting telescopes, since they use the property of refraction, or bending, of light ( see Optics: Reflection and Refraction ). The largest refracting telescope is the 40-in (1-m) telescope at the Yerkes Observatory in Williams Bay, Wisconsin, founded in the late 19th century. Lenses bend different colors of light by d...
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Infrared Astronomy - astronomy.
ft above sea level. With the launch of the Infrared Astronomical Satellite (IRAS), by the United States, the United Kingdom, and The Netherlands in 1983, infraredastronomy took another leap forward. This mission surveyed the entire sky at wavelengths of 12, 25, 60, and 100 microns (1 micron is a millionth of a meter) until itsonboard supply of liquid helium ran out. A short time later infrared astronomy was revolutionized by the first introduction of devices that could take infrared images. Thea...
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History of Astronomy - astronomy.
Egypt, the Sun was directly overhead at noon. On the same date and time in Alexandria, Egypt, the Sun was about 7 degrees south of zenith. With simple geometryand knowledge of the distance between the two cities, he estimated the circumference of the Earth to be 250,000 stadia. (The stadium was a unit of length, derivedfrom the length of the racetrack in an ancient Greek stadium. We have an approximate idea of how big an ancient Greek stadium was, and based on that approximationEratosthenes was...
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X-Ray Astronomy - astronomy.
Some neutron stars have weaker magnetic fields that allow incoming material to settle onto the entire surface of the neutron star. Eventually, so much material buildsup that the surface layer becomes dense enough to set off a vast thermonuclear explosion, called an outburst. The explosion heats gas to produce X rays. Such aneutron star—called an X-ray burster—can increase its X-ray production by a million times during an outburst. The X-ray glow fades over time, and the binary systementers a lon...
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Radio Astronomy - astronomy.
equivalent to the apparent angular dimensions of a basketball at the distance of the moon. In 1984, the U.S. government appropriated funds for the construction of aninstallation called the very long baseline array (VLBA), a network of 10 radio antennas spread from the U.S.-Canadian border to Puerto Rico and from Hawaii to the U.S.Atlantic coast. The VLBA is expected to provide angular resolutions in the range of 200-millionths of an arc second. Canada and Australia are both planning similarprogr...
- Constellation (astronomy) - astronomy.
- Callisto (astronomy) - astronomy.
- Ganymede (astronomy) - astronomy.
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- Europa (astronomy) - astronomy.
- Io (astronomy) - astronomy.
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Titan (astronomy) - astronomy.
The terrain is rugged and shows evidence of erosion from methane rain and from liquid seeping from underground. The rocklike ice chunks on the surface,photographed by Huygens, have a rounded shape that could result from their tumbling in flash floods. Scientists have also identified possible cold volcanoes that mayspew a mix of ammonia and water ice. Titan is Saturn’s densest moon. Planetary scientists theorize that Titan has a rocky core about 3,400 km (about 2,100 mi) in diameter, surrounded b...
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Star (astronomy) - astronomy.
absorbing the missing colors of light. For example, the set of dark lines made by hydrogen includes a dark red line, the set of dark lines made by sodium includes a pairof dark yellow lines, and the set of dark lines made by iron includes lines of nearly every color. Each element in the gaseous outer layer of a star produces its ownparticular pattern of dark spectrum lines, depending on the temperature and pressure of the gas. Astronomers have observed spectrum lines, or spectra, for hundredsof...
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Telescope - astronomy.
Observatory). In some telescopes designed in the 1990s, the mirror’s weight has been dramatically reduced by sandwiching a honeycomb pattern of glass ribs between a thin, butrigid, concave mirror and a flat back plate. Engineers have even developed meniscus mirrors—mirrors that are too thin to support their own weight. An adjustableframework supports the meniscus mirror, and servomechanical actuators, controlled by computer, continually adjust the shape of the mirror as it tracks celestial tar...
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Observatory - astronomy.
Ultraviolet radiation, X rays, and gamma rays have shorter wavelengths than visible light has. These types of radiation tell astronomers about the hottest and mostviolent phenomena in the universe. Earth’s atmosphere blocks most of this radiation, so astronomers must send their observatories above the atmosphere aboardballoons, rockets, or satellites. Ultraviolet telescopes are much like visible light telescopes, but X-ray telescopes must have special nested cylindrical mirrors to prevent Xrays...
- Orbit (astronomy and physics) - astronomy.
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Space Telescope - astronomy.
of its normal companion star and heating it to millions of degrees. See also X-Ray Astronomy; Chandra X-Ray Observatory. D2 Gamma-Ray Space Observatories Studying gamma rays offers scientists answers to some of the most perplexing questions about the explosive and dynamic physical processes in the universe. Gamma-ray observation also provides clues about the structure and dynamics of the Milky Way and other galaxies; the nature of pulsars, quasars, black holes, and neutronstars; and the orig...
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Relativity - astronomy.
beta, for example, might be as large as 0.5, and the mass of the electron doubled. The mass of a rapidly moving electron could be easily determined by measuring thecurvature produced in its path by a magnetic field; the heavier the electron, the greater its inertia and the less the curvature produced by a given strength of field ( see Magnetism). Experimentation dramatically confirmed Einstein's prediction; the electron increased in mass by exactly the amount he predicted. Thus, the kinetic ener...
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Gravitation - astronomy.
precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...
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Eclipse - astronomy.
bending of light rays passing close to the sun because of the sun’s gravitational field ( see Relativity). The great brilliance of the solar disk and the sun-induced brightening of the earth’s atmosphere make observations of the corona and nearby stars impossible except during a solar eclipse. The coronagraph, a photographictelescope, permits direct observation of the edge of the solar disk at all times. Today, scientific solar eclipse observations are extremely valuable, particularly when thepa...
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Interstellar Matter - astronomy.
silhouette of a cloud of dust. At other times, it blocks only a percentage of the light from behind it, a process known by astronomers as extinction . The long, narrow dark lanes in the Milky Way as seen from Earth are examples of extinction. The amount of extinction is different for different wavelengths of light. A2 Reddening Starlight that does not get completely absorbed by interstellar dust can still be changed by the dust’s effects. As light passes through less dense patches of interstel...
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Extrasolar Planets - astronomy.
When a planet passes in a front of the star it orbits—an event called a transit—it causes a small dip in the brightness of the star. Measuring the slight change in thebrightness can be used not only to directly detect a planet, but to determine its size and orbit. However, the planet needs to orbit in a plane that lies in a telescope’sline of sight on the star. Despite long odds, Earth-based telescopes have detected and studied a few exoplanets using this method. The first space telescope design...
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Voyager - astronomy.
Voyager 1 had not yet reached the termination shock boundary. They reported that the spacecraft was near but not yet there. Both teams agreed, nevertheless, thatVoyager 1 had entered unknown territory and had embarked on the final phase of its mission, which includes exploring the termination shock boundary, the heliopauseitself, and finally, interstellar space. Voyager 2 is also due to explore these outer regions. Unlike Voyager 1, a key instrument known as a plasma detector is still functionin...
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Astrobiology - astronomy.
water to help reactions along. American chemists Stanley Miller and Harold Urey tested part of Oparin and Haldane’s hypothesis in the early 1950s by simulating conditions of the early Earth. In whathas become known as the Miller-Urey experiment, the two scientists connected two flasks with a loop of glass tubing that allowed the gases to pass between the flasks.They filled the upper flask with methane, ammonia, and hydrogen—components thought to have been in the early atmosphere. They filled the...
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Supernova - astronomy.
The term hypernova has been proposed for an extremely massive core-collapse supernova—possibly more than 100 times the mass of the Sun. A hypernova is thought to form a black hole. Just before it explodes, a hypernova may release a huge burst of gamma rays in a jet from the rotating black hole at its center. These jets mayexplain the so-called long gamma-ray bursts detected by astronomers. According to some researchers, massive stars with over 40 solar masses may sometimescollapse directly int...
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- Pulsar - astronomy.
- Quasar - astronomy.
- Spacelab - astronomy.
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Astrophysics - astronomy.
Contributed By:George Brooks FieldMicrosoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.
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Kuiper Belt - astronomy.
III RESEARCH The Kuiper Belt is an exciting area of research in astronomy. The discovery and astronomical exploration of the Kuiper Belt over the past decade have fueled arevolution in scientists’ views of the solar system. Today astronomers recognize the Kuiper Belt as the third major region of the solar system (the other two regions arethe inner solar system, with its small rocky planets, and the outer solar system, with its gas-giant planets). They believe that the belt helps explain Pluto’...
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Astronaut - astronomy.
Every operation during a flight is important and interesting, but many might be boring to an observer. Much of an astronaut’s job is entering computer instructions,preparing samples, making measurements, recording data, fixing what breaks, and adjusting the checklist when something unexpected happens. Sometimes astronautsretrieve or repair satellites, rendezvous or dock with other spacecraft, and do important emergency repairs. The adaptability of the human crew is crucial to the successof missi...
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Neutron Star - astronomy.
about three times the full mass of the sun, the gravitational force will exceed the strength of the material, and the core will collapse until it disappears from the visibleuniverse altogether. This extreme state of gravitational collapse is known as a black hole. Astronomers speculate that neutron stars in interacting binary star systemscan become black holes by accumulating mass in the same way that white dwarf stars in interacting binary star systems become more massive. Contributed By:Dennis...
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Milky Way - astronomy.
Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.
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Planetary Science - astronomy.
III ORIGINS AND COMPOSITIONS OF PLANETS Astronomers believe that planetary systems are formed of elemental materials that were created in the interiors of giant stars. Some of this material comes from giantstars that shed material into space as they age. Most of the matter to form planets, however, comes from stars that explode as supernovas and spread debris enrichedwith the heavier chemical elements into space. According to the currently accepted views, the most likely first stage in the evo...
- Nebula - astronomy.
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NASA - astronomy.
Challenger shuttle after launch in 1986 and the Columbia shuttle during reentry in 2003, killing both crews. Investigations traced the accidents to design flaws and tomanagement problems. Both accidents led to design and procedure changes, and to a temporary stoppage of shuttle flights. Following the Columbia disaster, NASA alsoannounced plans to retire the shuttle in 2010, after completion of the International Space Station (ISS), a human orbital research facility. The Constellation program is...
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Galaxy - astronomy.
Astronomers have obtained images of young galaxies using the Keck Telescope in Hawaii and the Hubble Space Telescope, which resides in an orbit high above Earth’satmosphere and thus avoids atmospheric interference. Photos from the HST show galaxies that are as far as 13 billion light-years away from Earth, which means theyformed soon after the universe formed about 13.7 billion years ago. The galaxies appear to be spherical in shape, and may be early precursors of elliptical and spiralgalaxies....
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Nova - astronomy.
When first discovered, the spectrum of a nova shows that the expanding layers of gas that cause the brightening have temperatures of 40,000° to 50,000° C (70,000°to 90,000° F)—about eight times as hot as the surface of the Sun. By the time a nova reaches maximum brightness, the temperature of the material has fallen to about10,000° C (about 20,000° F), or lower. Just after maximum brightness, the escaping cloud of gas cools and expands enough to become transparent. This transparency allows astro...
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Cosmology - astronomy.
In 1917 American scientist Harlow Shapley measured the distance to several groups of stars known as globular clusters. He measured these distances by using amethod developed in 1912 by American astronomer Henrietta Leavitt. Leavitt’s method relates distance to variations in brightness of Cepheid variables, a class of starsthat vary periodically in brightness. Shapley’s distance measurements showed that the clusters were centered around a point far from the Sun. The arrangement of theclusters was...
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Sun - astronomy.
A The Sun’s Place in the Milky Way The Milky Way Galaxy contains about 400 billion stars. All of these stars, and the gas and dust between them, are rotating about a galactic center. Stars that arefarther away from the center move at slower speeds and take longer to go around it. The Sun is located in the outer part of the galaxy, at a distance of 2.6 × 10 17 km (1.6 × 10 17 mi) from the center. The Sun, which is moving around the center at a velocity of 220 km/s (140 mi/s), takes 250 million y...
- Binary Star - astronomy.
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Dark Matter - astronomy.
observed, and the measured frequency of such events has placed limits on how much dark matter can take the form of MACHOs. From the observations that have beenmade by astronomers, it is now known that MACHOs cannot be the dominant constituent of dark matter. There are simply not enough such gravitational lenses. Physicists suspect that a more exotic form of cold dark matter must exist. This form is not baryonic. Like neutrinos, this form barely interacts with ordinary matter, butis some type of...
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Solar System - astronomy.
dwarf planets according to the IAU because they have rounded shapes from their own gravity but have not cleared their neighborhoods in space of other objects—bothorbit through the Kuiper Belt, a region beyond Neptune containing thousands of small icy bodies. Pluto and Eris are composed of layers of ice around a rocky core.Ceres qualifies as a dwarf planet because it is spherical but is found in the asteroid belt, a zone between the orbits of Mars and Jupiter that contains thousands of smallrocky...
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Apollo Program - astronomy.
Moon’s orbit; rendezvousing and docking with the CSM; and finally, setting a course home to Earth. On return to Earth, the spacecraft was slowed by drag from Earth’satmosphere and by parachutes (just before splashdown), before landing in the ocean. The transit time to and from the Moon was approximately three days each way.Depending on the specific mission, the time in lunar orbit ranged from less than one day for Apollo 8 to over six days for the final three missions, and the time on thelunar s...
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Jupiter (planet) - astronomy.
Beneath the supercritical fluid zone, the pressure reaches 3 million Earth atmospheres. At this depth, the atoms collide so frequently and violently that the hydrogenatoms are ionized—that is, the negatively charged electrons are stripped away from the positively charged protons of the hydrogen nuclei. This ionization results in asea of electrically charged particles that resembles a liquid metal and gives rise to Jupiter’s magnetic field. This liquid metallic hydrogen zone is 30,000 to 40,000 k...
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Mars (planet) - astronomy.
The Martian core is probably much like Earth’s, consisting mostly of iron, with a small amount of nickel. If other light elements, particularly sulfur, exist there as well, thecore may be larger than presently thought. From studying Earth’s magnetic field and core, scientists theorize that the motions of the liquid rock in Earth’s core generateits magnetic field. Mars does not have a significant magnetic field, so scientists believe that Mars’s core is probably solid. However, spacecraft data in...
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Space Exploration - astronomy.
to produce 250,000 newtons (56,000 lb) of thrust. The Germans launched thousands of V-2s carrying explosives against targets in Britain and The Netherlands. Whilethey did not prove to be an effective weapon, V-2s did become the first human-made objects to reach altitudes above 80 km (50 mi)—the height at which outer spaceis considered to begin—before falling back to Earth. The V-2 inaugurated the era of modern rocketry. A2 Early Artificial Satellites During the years following World War II, the...
- Luna (space program) - astronomy.
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Infrared Space Observatory - astronomy.
know how often these disks occur around stars to help them understand how common it is for planets to form. ISO found several previously unknown stars with disks.ISO also detected olivine, a silicate mineral found in Earth’s own rocky mantle, in the comet Hale-Bopp, which was visible from Earth in 1996 and 1997. The discovery ofolivine in the comet suggests that the comet and Earth have a similar origin. The satellite also detected the first evidence of water outside of the solar system inplanet...
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- Hubble Space Telescope (HST) - astronomy.
- Sirius - astronomy.