Mercury, in astronomy
Mercury, in astronomy, nearest planet to the sun, at a mean distance of 36 million mi (58 million km); its period of revolution is 88 days. Mercury passes through phases similar to those of the moon as it completes each revolution about the sun, although the visible disk varies in size with respect to its distance from the earth. Because its greatest elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth...... Click the link for more information. is 28°, it is seen only for a short time after sunset or before sunrise. Since observation of Mercury is particularly unfavorable when it is near the horizon, the planet has often been studied in full daylight, with the sun's light blocked off. Mercury has the most elliptic orbit of the planets in the solar system. Its great eccentricity of orbit and its great orbital speed provided one of the important tests of Einstein's general theory of relativity relativity, physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two systems or frames of reference.
..... Click the link for more information. . Mercury's perihelion (its closest point to the sun) is observed to advance by 43" each century more than can be explained from planetary perturbations using Newton's theory of gravitation gravitation, the attractive force existing between any two particles of matter .
The Law of Universal Gravitation
Since the gravitational force is experienced by all matter in the universe, from the largest galaxies down to the smallest particles, it
..... Click the link for more information. , yet in nearly exact agreement with the prediction of the general theory. Mercury is the smallest planet in the solar system, having a diameter of about 3,000 mi (4,800 km); both Jupiter's moon Ganymede and Saturn's moon Titan are larger. Its mean density is comparable to that of the earth. Its small mass and proximity to the sun prevent it from having an appreciable atmosphere, although a slight amount of carbon dioxide has been detected. The surface of Mercury is much like that of the moon, as was shown during the Mariner 10 spacecraft flyby in 1974. Most of its craters were formed during a period of heavy bombardment by small asteroids early in the solar system's history. It was long thought that Mercury's period of rotation on its axis was identical to its period of revolution, so that the same side of the planet always faced the sun. However, radar studies in 1965 showed a period of rotation of 58.6 days. This results in periods of daylight and night of 90 earth days each, with the daylight temperatures reaching as high as 800°F; (450°C;). Night temperatures are believed to drop as low as −300°F; (−184°C;).
Mercury, in Roman religion
Mercury, in Roman religion, god of commerce and messenger of the gods; identified with the Greek Hermes Hermes, in Greek religion and mythology, son of Zeus and Maia. His functions were many, but he was primarily the messenger of the gods, particularly of Zeus, and conductor of souls to Hades...... Click the link for more information. . He was honored at the Mercuralia, a festival held in May and attended primarily by traders and merchants.
mercury, chemical element
mercury or quicksilver [from the Roman god Mercury], metallic chemical element; symbol Hg [Lat. hydrargyrum=liquid silver]; at. no. 80; at. wt. 200.59; m.p. −38.842°C;; b.p. 356.58°C;; sp. gr. 13.55 at 20°C;; valence +1 or +2. Mercury was discovered in antiquity, and was known to the ancient Chinese, Hindus, and Egyptians, but was not recognized as an element. It was used as a medicine by Paracelsus. It was first recognized as a chemical element (in the modern sense) by A. L. Lavoisier about the end of the 18th cent.Properties
Mercury is the only common metal existing as a liquid at ordinary temperatures. The pure metal has a silver-white mirrorlike appearance. Mercury is below cadmium in Group 2 of the periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley . In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the
..... Click the link for more information. . It is relatively stable in dry air, but in moist air slowly forms a gray oxide coating. Mercury has high surface tension; when spilled, it breaks up into tiny beads which often become lodged in cracks.
Compounds
Mercury forms numerous compounds, assuming +1 valence in mercurous compounds and +2 valence in mercuric compounds. Mercury is not attacked by dilute hydrochloric or sulfuric acid. It reacts with hot nitric acid to form mercuric nitrate, Hg(No3)2. An excess of mercury reacts with nitric acid to form mercurous nitrate, HgNO3. Mercury reacts with hot concentrated sulfuric acid to form mercuric sulfate, HgSO4; with excess mercury, mercurous sulfate, Hg2SO4, is formed. Mercury reacts directly with the halogens to form mercuric salts. At elevated temperatures mercury reacts slowly with oxygen to form mercuric oxide, HgO. A mercurous oxide may be formed chemically but is unstable, decomposing to a mixture of mercury and mercuric oxide.
Natural Occurrence and Uses
Mercury occurs uncombined in nature to a limited extent. The metal is obtained commercially from cinnabar cinnabar (sĭn`əbär), mineral, the sulfide of mercury, HgS.
..... Click the link for more information. , a mercuric sulfide ore; it is easily separated by roasting the ore in air. The metal is usually purified by repeated vacuum distillation.
Mercury metal has many uses. Because of its high density, it is used in barometers barometer (bərŏm`ətər), instrument for measuring atmospheric pressure.
..... Click the link for more information. and manometers. Because it has a high rate of thermal expansion that is fairly constant over a wide temperature range, it is used extensively in thermometers thermometer, instrument for measuring temperature . Galileo and Sanctorius devised thermometers consisting essentially of a bulb with a tubular projection, the open end of which was immersed in a liquid.
..... Click the link for more information. . Mercury is important as a liquid contact material for electric switches. It is used in mercury-vapor lamps, which emit light rich in ultraviolet radiation; various kinds of such lamps are used for street lighting, as sun lamps, and in "black lights" (see lighting lighting, light produced by artificial means to allow visibility in enclosures and at night. For stage lighting, see scene design and stage lighting .
Early Sources of Artificial Lighting
..... Click the link for more information. ). Mercury is used as an electrode in the production of chlorine and sodium hydroxide. It is also used in certain electric batteries. With some other metals mercury forms a special type of alloy called an amalgam amalgam (əmăl`gəm), alloy containing mercury .
..... Click the link for more information. ; a special amalgam (mostly mercury, silver, and tin) is used in dentistry for filling teeth.
Mercury compounds have many uses. Calomel (mercurous chloride mercurous chloride, mercury (I) chloride, or calomel, chemical compound, Hg2Cl2, a white crystalline powder, very slightly soluble in water.
..... Click the link for more information. , Hg2Cl2) is used as a standard in electrochemical measurements and in medicine as a purgative. Mercuric chloride mercuric chloride or mercury (II) chloride, chemical compound, HgCl2, a white powder of colorless rhombohedral crystals, somewhat soluble in water. It is also called bichloride of mercury or corrosive sublimate.
..... Click the link for more information. (corrosive sublimate, HgCl2) is used as an insecticide, in rat poison, and as a disinfectant. Mercuric oxide is used in skin ointments. Mercuric sulfate is used as a catalyst in organic chemistry. Vermilion vermilion, vivid red pigment of durable quality. It is a chemical compound of mercury and sulfur and is known as red sulfide of mercury; it was formerly obtained by grinding pure cinnabar but is now commonly prepared synthetically.
..... Click the link for more information. , a red pigment, is mercuric sulfide; another crystalline form of the sulfide (also used as a pigment) is black. Mercury fulminate fulminate (fŭl`mĭnāt), any salt of fulminic acid, HONC, a highly unstable compound known only in solution.
..... Click the link for more information. , Hg(CNO)2, is used as a detonator. Mercury forms many organic compounds. Mercurochrome (in 2% aqueous solution) is used in medicine as a topical antiseptic. Mercury compounds were formerly used in the treatment of syphilis syphilis (sĭf`əlĭs), contagious sexually transmitted disease caused by the spirochete Treponema pallidum
..... Click the link for more information. .
See also mercury poisoning mercury poisoning, tissue damage resulting from exposure to more than trace amounts of the element mercury or its compounds. Elemental mercury (the silver liquid familiar from thermometers) is the most common occupational source.
..... Click the link for more information. .
mercury
or quicksilverMetallic chemical element, chemical symbol Hg, atomic number 80. Mercury is the only elemental metal that is liquid at ordinary temperatures, with a freezing point of −38 °F (−39 °C) and a boiling point of 674 °F (356.9 °C). Silvery white, dense, toxic (see mercury poisoning), and a good conductor of electricity, mercury is occasionally found free in nature but usually occurs as the red sulfide ore, cinnabar (HgS). It has many uses—in dental and industrial amalgams, as a catalyst, in electrical and measuring apparatus and instruments (e.g., thermometers), as the cathode in electrolytic cells, in mercury-vapour lamps, and as a coolant and neutron absorber in nuclear power plants. Many of mercury's compounds, in which it has valence 1 or 2, are pigments, pesticides, and medicinals. It is a dangerous pollutant because it concentrates in animal tissues in increasing amounts up the food chain.
Mercury
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Mercury
Innermost planet of the solar system. Its average distance from the Sun is about 36 million mi (58 million km), but its highly elliptical orbit carries it 7.5 million mi (12 million km) nearer to and farther from the Sun. It is the smallest major planet, having a diameter of about 3,030 mi (4,880 km) and a mass about one-eighteenth of Earth's. With the shortest period of revolution (only 88 Earth days) and the highest average orbital speed (30 mi/sec [48 km/sec]) of any planet, it is aptly named after the Roman fleet-footed messenger god. It spins very slowly, making one complete rotation relative to the stars every 59 Earth days, while its solar day (from one sunrise to the next) is 176 Earth days, owing to its revolution around the Sun. Its surface is heavily cratered. Its most impressive feature is perhaps the 800-mi (1,300-km) Caloris Basin, formed by a huge meteorite impact. Mercury also has steep cliffs that extend for hundreds of miles. The discovery of a magnetic field in its vicinity suggests it has a large iron core, which would account for a mean density almost as high as Earth's. Its atmosphere is negligible; its surface gravity, about one-third that of Earth's, holds an exceedingly tenuous layer of gases. Temperatures at its surface change dramatically, ranging from a high that can exceed 800 °F (425 °C) on the sunward side to a low of about −290 °F (−180 °C) at the end of its night.
Mercury
First series of U.S. manned spaceflights (1961–63), which began about three weeks after Yury A. Gagarin became the first human in space. In May 1961 Alan B. Shepard rode the first Mercury space capsule, Freedom 7, on a 15-minute, 302-mi (486-km) suborbital flight, attaining a maximum altitude of 116 mi (186 km). The first U.S. manned flight in orbit was that of the Friendship 7, carrying John H. Glenn, Jr., in February 1962; it completed three orbits. The last Mercury flight, Faith 7, launched in May 1963, was the longest, making 22 orbits in about 34 hours.
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