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in Roman religion, god of commerce and messenger of the gods; identified with the Greek HermesHermes,
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.
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. He was honored at the Mercuralia, a festival held in May and attended primarily by traders and merchants.


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 elongationelongation,
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.
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 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 relativityrelativity,
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.
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. 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 gravitationgravitation,
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 is often called
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, 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 3,031 mi (4,878 km); both Jupiter's moon Ganymede and Saturn's moon Titan are larger. Its mean density relatively high, a little less than that of the earth; its core is believed to occupy about 85% of its radius and to consist of a probably solid iron core, surrounded by a liquid iron layer, which is surrounded by a solid iron-sulfide layer. There is 10 times as much sulfur in its crust than is found on the surface of the earth. The planet has a dark surface that reflects relatively little light; it is believed that the surface has been darkened by the deposition of carbon-rich micrometeorites that originate from comets passing close to the sun. Mercury's 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 Mariner 10 in flybys in 1974–75 and Messenger in flybys in 2008–9 and in orbit in 2011–15. Most of its craters were formed during a period of heavy bombardment by small asteroids early in the solar system's history. Messenger, which became the first space probe to orbit Mercury, found solid evidence of ancient volcanism as well and corroborated that there is ice near the planet's north pole in craters where areas are in permanent shadow; measurements by earth-based radar in the 1990s had suggested that there was ice near the poles. Images from Messenger were used to produce (2016) a complete topographic map of Mercury.

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 88 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;).




[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.


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 tableperiodic 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 table entitled
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. 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.


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 cinnabarcinnabar
, mineral, the sulfide of mercury, HgS. Deep red in color, it is used as a pigment (see vermilion), but principally it is a source of the metal mercury. It is mined in Spain, Italy, and in the United States in California.
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, 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 barometersbarometer
, instrument for measuring atmospheric pressure. It was invented in 1643 by the Italian scientist Evangelista Torricelli, who used a column of water in a tube 34 ft (10.4 m) long.
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 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 thermometersthermometer,
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.
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. 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 lightinglighting,
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
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). 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 amalgamamalgam
, alloy containing mercury. The alloy may be liquid or solid, depending on the proportion of mercury, although all naturally occurring amalgams, i.e., those of gold and silver, are solid. Amalgams are widely used.
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; a special amalgam (mostly mercury, silver, and tin) is used in dentistry for filling teeth.

Mercury compounds have many uses. Calomel (mercurous chloridemercurous chloride,
 mercury (I) chloride,
or calomel,
chemical compound, Hg2Cl2, a white crystalline powder, very slightly soluble in water.
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, Hg2Cl2) is used as a standard in electrochemical measurements and in medicine as a purgative. Mercuric chloridemercuric 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. It is extremely poisonous.
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 (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. Vermilionvermilion,
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.
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, a red pigment, is mercuric sulfide; another crystalline form of the sulfide (also used as a pigment) is black. Mercury fulminatefulminate
, any salt of fulminic acid, HONC, a highly unstable compound known only in solution. The term is most commonly applied to the explosive mercury (II) fulminate, also called fulminate of mercury, Hg(ONC)2. The pure compound forms white cubic crystals.
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, 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 syphilissyphilis
, contagious sexually transmitted disease caused by the spirochete Treponema pallidum (described by Fritz Schaudinn and Erich Hoffmann in 1905). Syphilis was not widely recognized until an epidemic in Europe at the end of the 15th cent.
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See also mercury poisoningmercury 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.
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(mer -kyŭ-ree) The innermost and, with a diameter of 4878 km, the second smallest planet in the Solar System, orbiting the Sun in 87.97 days at an average distance of 0.39 AU. It has no natural satellite. The distance from the Sun varies between 0.31 and 0.47 AU because of Mercury's high orbital eccentricity of 0.21. Maximum elongation from the Sun varies between 28° and 18°, so that Mercury can be observed only when low in the twilight sky. Telescopes reveal a disk, between 4.5 and 12.9 arc seconds across, showing vague markings and phases varying from full at superior conjunction to new at inferior conjunction. Transits across the Sun's disk recur at intervals of 7 or 13 years or in combinations of these figures. Orbital and physical characteristics are given in Table 1, backmatter.

Mercury's axial rotation period of 58.64 days, determined by radar in 1965, corresponds almost exactly to ⅔ of its orbital period, a fact discovered in 1965 by the Italian astronomer Giuseppi Colombo. The phenomenon is probably due to tidal coupling between the extra gravitational force of the Sun at perihelion and irregularities in Mercury's almost perfectly spherical form. This rotation period is close to half the planet's synodic period; this explains why early observers, who saw the same face of the planet at favorable oppositions, concluded erroneously that it had a synchronous rotation period of 88 days.

Mariner 10, which made three close approaches to Mercury in 1974 and 1975, measured a maximum daytime temperature of 190 °C; this may reach 450 °C near perihelion. At night temperatures plunge to –180 °C beneath the most tenuous of atmospheres, consisting mainly of minute traces of helium, oxygen, and argon, plus some sodium and potassium. Mariner found that Mercury has a magnetosphere supported by a magnetic field about 1% as strong as the Earth's; it is not clear whether this is generated within the planet's core or arises from permanent magnetization within the crust. Mercury's density, 5.4 times that of water, implies that it has a large nickel–iron core, perhaps 3600 km across.

Photography of half of Mercury's surface by Mariner 10 shows it to resemble the Moon in being heavily cratered with intervening areas of lava-flooded plains, called maria. The largest impact feature detected is the 1300 km diameter Caloris Basin, similar to the Moon's Mare Imbrium. Antipodal to Caloris is an area of chaotic terrain created, it is believed, by shock-waves from the same impact. Some recent craters possess radiating systems of light-colored surface streaks, similar to the lunar rays. The ejecta blankets surrounding many craters are half the size of those around lunar craters of similar diameter, probably because Mercury has twice the Moon's surface gravity. Of particular interest, and not seen on the Moon or Mars, are lines of cliffs, called lobate scarps, up to 3 km high and 500 km long. These may have resulted from wrinkling of the silicate-rich crust as Mercury's core cooled and contracted billions of years ago.

Enlarge picture
A detail of Mercury shown holding two caduceus rods. From an engraving in Maiers’ Atalanta Fugiens, 1618. Reproduced by permission of Fortean Picture Library.


(religion, spiritualism, and occult)

Mercury is the closest planet to the Sun with an orbit of 88 days. It is a small planet only 3,000 miles in diameter. Because of its proximity to the Sun, Mercury can never be more than 27° away from the Sun in an astrological chart. Therefore Mercury can only be observed shortly before sunrise or shortly after sunset, and even then it is difficult to see.

The name Mercury is from the Latin term Mercurius. In the older Greek he is known as Hermes. In Mesopotamia he is known as Nabu, the divine scribe of destiny. In the Vedic culture he is known as “Budha,” meaning “intellect,” as opposed to Buddha, meaning “enlightened one.” In ancient Europe Mercury is associated with Odin, the king of the gods.

Of all the planets, Mercury has the most versatile and varied iconography. Mercury is youthful, clever, and often represented as a trickster. He is called both the messenger of the gods and the king of thieves. He is a scribe for the fates, the god of communication, and the god of magic. Because he moves so quickly in the sky and appears to jump to either side of the Sun, he is sometimes a morning star, and sometimes an evening star. This visible trait makes Mercury a chameleon, a planet that is easily influenced by other planets. Mercury is technically neutral in gender although some cultures portray him as a hermaphrodite, half man and half woman.

In Greek mythology Mercury is known for the amazing feats he performed immediately after his birth to Zeus and Maia. One version of the story describes how the newborn discovers a tortoise. He invites the tortoise to join him for a meal followed by music. The tortoise hesitates but soon falls for Mercury’s wiles. The child god then kills the tortoise, invents fire to cook the meat, and creates a lyre (harp) out of the animal’s carapace. Later the same day he steals fifty of Apollo’s cows and sacrifices two of them. When the theft and the thief are discovered, Mercury offers the lyre to Apollo in retribution. It is Apollo’s turn to be enchanted by the child, and he gives him the title king of thieves.

From the word Mercury come the words merchant, mercenary, and commerce. It is not only Mercury’s charm that won over the offended Apollo, but also his exchange of items: the lyre for two cows. Mercury is an opportunist and loves to wheel and deal. He rules quick transactions and the marketplace. He is the messenger of the gods, delivering Hera, Aphrodite, and Athena to the judgment of Paris, which led to the Trojan War. This demonstrates the mercenary aspect of Mercury. The gods knew that nothing good would come out of the contest, but Mercury performed the deed for the right price.

When Zeus (Jupiter) sojourns on Earth, his favorite companion is Mercury because he is clever, knows how to have a good time, and is skillful. It was Zeus who gave Mercury the winged sandals, and the claduceus that became the symbol of healing and medicine. Mercury is associated with the healing arts, but in Greece he was also associated with death. He could travel between all the worlds, and was responsible for guiding the dead safely and swiftly to the underworld. He was known as the psychopompos who assisted in the transition between different states of reality. In this sense, Hermes functions as a hospice worker.

There are similarities in Hinduism with Mercury’s association with the god Visnu. In the Rig Veda, Visnu marks out the three worlds with three giant strides spanning the heavens, the earth, and the netherworld. Mercury, as a reincarnation of Visnu, quantifies or defines the different worlds. The Hindu Puranas, like the Greek myths, tell a wonderful story of the birth of Mercury. Jupiter was the guru (teacher) to the gods, and one of his students was the Moon. The beautiful Tara (Star) was married to Jupiter, but fell in love with the Moon. The tryst soon produced a child who was Mercury. Mercury was so delightful and charming that everyone loved him. Both Jupiter and the Moon claimed to be the father of the wonderful child. Mercury has two fathers, and rules the two mutable signs of Gemini and Virgo.

Mercury is also the son of Jupiter in Mesopotamian mythology. Here he is known as Nabû, the scribe of the gods. On the eighth day of the new year, all the gods come together to decide the fate for the coming year. It was NAbû who wrote down the destinies, and thus fixing the fates. NAbû was also a diplomat. One tablet reads, “NAbû who holds the god’s Table of Destiny, and can reconcile conflicting things.”

By the time of Hellenistic Egypt (300 b.c.e.) Mercury becomes associated with the god Thoth. This god was responsible for all areas of science including medicine, astronomy and astrology, architecture, and magic. Thoth played an important role in Egyptian afterlife. At the time of death a person’s soul was magically weighed to determine if he or she had lived a good or bad life. It was Thoth’s assignment to document the outcome.

In Alexandria Egypt, around the second century b.c.e., a new form of mysticism was developing from a mixture of Egyptian, Near Eastern, and Greek philosophy. The primary text is known as the “Corpus Hermeticum” and is attributed to Hermes Trismegistus, or the Great-Great-Great Hermes. These Hermetic texts were crucial in the development of astrology and resulted in the development of today’s natal astrology. The texts describe the development of the soul through reincarnations that are given qualities based on the planets. Later these writings would evolve into the philosophy of alchemy.

In Europe the god associated with the planet Mercury is the Celtic Lug, known as Odin, or Wotan to the Germanic peoples. He is the master of fine speech, magic, poetry and music, as well as wealth. He is known as the king of the gods, but is also the god of the underworld. His Valkyries transport dead warriors to Valhalla where they celebrate their bravery and conquests. In various myths Odin is shown as an old man wandering the Earth, or exchanging an eye for the wisdom of the world.

Mercury rules all forms of thought and communication. It also represents childhood, education, language, the intellectual mind (as compared to the emotional mind represented by the Moon), movement, business, healing, humor, music and dance, and the derivatives of these key words. For example the key word “language” includes vocabulary, speech, grammar, writing, foreign languages, prose and poetry, oration, understanding, and debate. “Business” includes the concepts of money, exchange or barter, mathematics, marketing, and legal issues pertaining to business.

Mercury rules the zodiac signs of Gemini and Virgo. The mutable nature of these signs is indicative of Mercury’s changeable nature. Gemini is an air sign and expresses the mental or intellectual quality of Mercury. Virgo is an earth sign and represents the manual dexterity of Mercury as well as the practical application of knowledge, primarily through service. Mercury is exalted at 15° of Virgo, and in debilitation or fall in the sign of Pisces.

A well-aspected or-placed Mercury will give the native a keen intellect, excellent business skills, and a fine sense of humor. The native can enjoy great diplomatic skills, and excel in logic and debate. They may love to travel and find pleasure in new experiences of all kinds. A weakly placed or aspected Mercury will give a wavering mind that is unable to make decisions. Speech may be affected resulting in harsh or rash language, or excessive gossip.

Mercury in a positive sense is adaptable, but in a negative sense is easily influenced. Close conjunctions and aspects of Mercury with other planets will change the expression of Mercury to a great degree. The one exception is the Sun. Because Mercury spends so much time near the Sun, he can “defend” his self-identity more readily.

Wherever Mercury falls in an astrological chart indicates the area of life where communication is crucial. The house position indicates the field of life where such communication will occur or needs to be developed, while the sign position gives insight into the nature or manner of the communication. Mercury placed in the fifth house indicates communication that is creative, and may involve or be directed at children or lovers. Mercury in the tenth house directs communication to achieve career goals and ambitions, and dealings with people in authority. Mercury placed in the sign of Taurus provides communication that is fixed, focused, and materially practical. Mercury placed in the sign of Gemini is versatile, interested in anything, quick and abstract in communication.

The transits of Mercury are quite fast and thus are not considered very strong. However, the houses and signs of transiting Mercury can indicate areas that are speeded up and activated. These areas or topics of life may experience more communication or thought, and in general require more attention.

There is much discussion about the effects of retrograde planets. The planet Mercury retrogrades on average three times per year, more than any other planet. In the natal chart a retrograde Mercury indicates an introspective mind where there can be more interior dialog than exterior. The individual may experience very deep thoughts, yet have difficulty communicating the depth of their conceptualizations. According to Vedic astrology retrograde planets are considered stronger because they are closer to the Sun.

In mundane astrology retrograde Mercury is often thought of as a negative transit period when there is confusion in communication and decisions will be challenged or undone. Popular culture believes that when Mercury is retrograde, car keys are mislaid, computers crash, and letters are lost. It may be more accurate to say that during these periods people can be distracted due to mental exertion, and this can lead to various mishaps.


Campion, Nicholas, and Steve Eddy. The New Astrology: The Art and Science of the Stars. New Pomfret, VT: Trafalgar Square Publishing, 1999.
Hamillton, Edith. Mythology: Timeless Tales of Gods and Heroes. New York: Signet Classics, 1942.
Hinnells, John R., ed. The Penguin Dictionary of Religions. London: Penguin Books, 1984.
Hornblower, Simon, and Antony Spawforth, eds. The Oxford Classical Dictionary. Oxford, Eng.: Oxford University Press, 1996. Reprint, 1999.
Mani, Vettam. Puranic Encyclopaedia. Delhi, India: Motilal Banarsidass Publishers, 1964.
Miller, Susan. Planets and Possibilities: Explore the Worlds Beyond Your Sun Sign. New York: Warner Books, 2001.
Wolkstein, Diane, and Samuel Noah Kramer. Inanna: Queen of Heaven and Earth, Her Stories and Hymns from Sumer. New York: Harper and Row, 1983.

—Maire Masco



the planet of the solar system that is closest to the sun; astronomical symbol, Mercury . Mercury is the smallest planet and has a diameter of 4,865 km (0.38 of the earth’s diameter), a mass of 3.304 X 1023 kg (0.055 of the earth’s mass, or 1/6,025,000 of the sun’s mass), and a mean density of 5.52 g/cm3. It is a terrestrial planet.

Mercury revolves around the sun at a mean distance of 0.387 astronomical units (58 million km) in an elliptical orbit with high eccentricity (e = 0.206). At perihelion its distance from the sun is 46 million km, and at aphelion 70 million km. Mercury’s period of revolution is 88 days. Recently (in the 1960’s) it was established, by means of radar observations, that Mercury rotates about its axis in a forward direction (that is, in the same direction as its orbital motion) with a period of 58.65 days (with respect to the stars). The length of the solar day on Mercury is 176 earth days. The angular velocity of Mercury’s axial rotation is 3/2 of the orbital velocity and corresponds to the angular velocity of the planet’s motion in orbit when Mercury is at perihelion. On this basis we may assume that the rotational velocity of Mercury is due to tidal forces from the sun.

Mercury is a difficult object to observe from the earth since it is never visually further from the sun than 28°. Consequently, Mercury must always be observed against a background of morning or evening twilight, low above the horizon. Moreover, at this time the planet’s phase—that is, the angle at the planet between the directions to the sun and to the earth—is close to 90° and the observer sees only half of its disk illuminated. For this reason, only large dark patches of an unknown nature have been recorded on the surface of Mercury, and only a most general map of the planet has been compiled.

Mercury’s equator is inclined to the orbital plane by 7°. During observations at elongations, that is, the greatest angular distance from the sun, Mercury has a brightness ranging from — 0.3 to +0.6 stellar magnitude. The observed variations in brightness with phase occur in a manner similar to that of the moon. This indicates the identical nature of the irregularities of these celestial bodies. However, the reflectivity of Mercury is poorer than that of the moon and resembles that of the lunar maria. Mercury’s spherical albedo is 0.058 (visual) and 0.09 (thermal). The cross section of the disk of Mercury determined by radar in the decimeter wavelength region is only 0.06 of the geometric cross section.

Mercury may lack an atmosphere, although polarization and spectral observations indicate the presence of a thin one. Indications of the presence of carbon dioxide, CO2, have been observed on Mercury by spectral analysis. The upper limit of the CO2 content is 4 g/cm . Nitrogen, NI, or argon, A2, which have not been detected spectroscopically in observations from the earth, may be mixed in. The content of these gases may be several times greater than that of CO 2. In Mercury’s upper atmosphere carbon dioxide should dissociate into CO, O, and O2 on exposure to strong ultraviolet radiation from the sun. At a high kinetic temperature these atoms and molecules may easily fly into interplanetary space, since the escape velocity on Mercury is very low —4.3 km/sec.

The computed average temperature on Mercury, determined on the assumption that the planet radiates as much heat as it receives from the sun, is 505°K at the mean distance from the sun. For the point on the surface of Mercury where the sun is in the zenith—the subsolar point—the calculated temperature is 618°K and the actually measured temperature is 613°K. This temperature increases to 700°K when Mercury is at perihelion and decreases to 550°K at aphelion. The infrared radiation from the unilluminated portion of Mercury, which was measured with great difficulty, yields a nighttime temperature on Mercury of about 110°K. This may be somewhat higher but can hardly be greater than 150°K. Average (for the disk of Mercury) temperatures up to 400°K in the centimeter wavelength region and lower temperatures, 300°-200°K, in the millimeter and decimeter wavelength regions, have been observed in measurements of Mercury’s thermal flux in the radio-frequency band. But these measurements pertain to some (shallow) level beneath the surface rather than to the surface itself. This has also been confirmed by the absence of a noticeable phase effect in the measured thermal fluxes. Comparison with the fluxes measured in the infrared region of the spectrum makes it possible to derive a value of the coefficient of thermal conductivity between 1/500 and 1/700, which corresponds to similar values for the moon.

The surface of Mercury should be compared to the lunar surface with caution, since the mean density of Mercury is much greater than that of the moon. The existence of matter with a density much greater than that on the surface must be assumed in the composition of Mercury’s crust or mantle. This may be iron, either mixed with silicates or forming an independent core. The latter, however, is unlikely, since the mass of Mercury is small and radioactive decay cannot be effective, so that the iron cannot be molten. Unfortunately, none of these conclusions can be quantitatively verified, since neither the flattening of Mercury’s figure nor the planet’s rotational moment is known. Mercury has no satellites.


Moroz, V. I. Fizika planet. Moscow, 1967.




in ancient Roman mythology, the god of commerce and the patron of travelers. Mercury was depicted carrying a staff and wearing winged sandals and a traveler’s hat. He corresponds to Hermes in ancient Greek mythology.



the first American single-seat manned spacecraft for orbital flights around the earth; also, the Mercury development and launch program (1959-63). The primary task of the Mercury series was to place a manned satellite in geocentric orbit and effect its safe return to earth. It was also necessary to study the possibilities for men to work in outer space.

The launch weight of the Mercury was more than 1,800 kg (including the emergency rescue system). The cabin volume (free volume) was 1.4 cu m; height (excluding the emergency rescue system), 2.9 m; maximum diameter, 1.8 m; and minimum diameter, 0.66 m. Its lift-drag ratio was zero. The Mercury landed in water on uncontrolled parachutes. The astronaut controlled the ship by means of a manual system connected in parallel with an automatic control system. He was also able to start the retrojet and open the braking parachute manually.

In the period from Sept. 9, 1959, to Nov. 29, 1961, before the first manned Mercury spacecraft was orbited with an astronaut on board, 15 launches were made on a ballistic trajectory, three spacecraft were placed in orbit, and one satellite—the Mercury Scout, designed to test the operation of tracking stations—was launched. The flights of manned experimental spacecraft in ballistic trajectories with Redstone rockets (A. Shepard, May 5, 1961, and V. Grissom, July 21, 1961) were the most important of these. The first flight lasted 15 min; the second, 16 min. The launches of Mercury spacecraft by the Atlas D launch vehicle between Feb. 20, 1962, and May 15, 1963, are listed in Table 1.




Hg, a chemical element in Group II of Mendeleev’s periodic system. Atomic number, 80; atomic weight, 200.59. Mercury is a silvery white heavy metal and is a liquid at room temperature. In nature, it is a mixture of seven stable isotopes with mass numbers 196 (0.2 percent), 198 (10.0 percent), 199 (16.8 percent), 200 (23.1 percent), 201 (13.2 percent), 202 (29.8 percent), and 204 (6.9 percent).

Native mercury was known in 2000 B.C. to the people of ancient India and China. Like the Greeks and Romans, they used cinnabar (native HgS) as a dye, drug, and cosmetic. The Greek physician Dioscorides in the first century A.D. heated cinnabar in an iron vessel fitted with a cover and obtained mercury vapor, which then condensed on the cool inner surface of the cover. The reaction product was called hydrargyros (Greek hydor, “water” and argyros, “silver”), that is, “liquid silver,” which is the origin of the Latin name hydrargyrum as well as of argentum vivum (quicksilver). This notion was later retained in the English “quicksilver” and the German Quecksilber. The origin of the Russian name for mercury, rtut’, has not been established.

Alchemists considered mercury a major component of all metals. The “fixation” of mercury, that is, the conversion of mercury to the solid state, was regarded as the first requirement for mercury’s conversion into gold. Solid mercury was first obtained in December 1759 by the St. Petersburg academicians I. A. Braun and M. V. Lomonosov, who managed to freeze mercury in a mixture of snow and concentrated nitric acid. In the experiments of Lomonosov, solid mercury was found to be as malleable as lead. News of the “fixation” of mercury created a sensation in the scientific world, for here was one of the most convincing proofs that mercury is similar to other metals.

In the earth’s crust, the average content of mercury, one of the extremely rare elements, is approximately 4.5 X 10-6 percent by weight. Mercury is present in approximately the same concentration in igneous rocks. The migration of mercury in the gaseous state and in aqueous solutions plays an important role in the element’s geochemistry. In the earth’s crust, mercury is for the most part dispersed; it precipitates from hot underground waters and forms ores, in which the mercury content amounts to several percent. Chief among the 35 known mercury minerals is cinnabar (HgS).

In the biosphere, mercury is mostly scattered and is sorbed only in insignificant quantities by clays and silts. The average content of mercury in clays and shales is 4 X 10-5 percent, and inseawater, 3 × 10-9 percent.

Native mercury is formed through the oxidation of cinnabar into a sulfate and the subsequent decomposition of the sulfate. The decomposition can result from either a volcanic eruption or, more commonly, from a hydrothermal process, where mercury separates from aqueous solutions.

Mercury is the only metal that is a liquid at room temperature. Solid mercury forms rhombohedral crystals, where a= 3.463 angstroms (A) and c= 6.706 A. The density is 14.193 g/cm3 for solid mercury at - 38.9°Cand 13.52 g/cm3 for liquid mercury at 20°C. The atomic radius of mercury is 1.57 A, and the ionic radius of Hg2+ is 1.10 Å. The element’s melting point is - 38.89°C, and the boiling point is 357.25°C. The specific heat capacity of mercury at 0°C is 0.139 kilojoule per kilogram per degree Kelvin (kJ/kg-°K), or 0.03336 calorie per gram per degree centigrade (cal/g.°C); at 200°C it is 0.133 kJ/kg-°K (0.0319 cal/g-°C). The coefficient of thermal expansion is 1.826 X 10-4 in the range 0°-100°C, and the thermal conductivity is 8.247 watts per meter per degree Kelvin (W/m•°K), or 0.0197 cal/cm•sec•°C. The resistivity of mercury at 0°C is 94.07 × 10-8 ohm•m (94.07 X 10-6 ohm•cm)• Mercury, which becomes a superconductor at 4.155°K, is diamagnetic, with an atomic magnetic susceptibility of - 0.19 X 10-6 at 18°C.

The configuration of the outer electrons of the mercury atom is 5d10 6s2, in accordance with which the cations Hg2+ and Hg22+ are formed in chemical reactions. The chemical reactivity of mercury is low. In dry air (or oxygen) mercury retains its luster indefinitely at room temperature. The two compounds mercury gives with oxygen are black mercurous oxide, Hg2O, and red mercuric oxide, HgO. Mercurous oxide appears as a black layer on the surface of mercury upon the action of ozone. Mercuric oxide is formed by heating mercury in the air at a temperature of 300°–350°C or by a careful heating of the nitrate Hg(N03)2 or Hg2(NO3)2. Hydroxides of mercury are practically nonexistent. Upon interaction with metals wetted by mercury, amalgams are formed. Of the mercury compounds containing sulfur, HgS is the most important and is obtained by grinding mercury with sublimed sulfur at room temperature as well as by precipitation from solutions of Hg2+ salts with the addition of hydrogen sulfide or the sulfide of an alkali metal. With halogens (chlorine, iodine), mercury reacts upon heating to form practically nondissociating and, in most cases, poisonous compounds of the HgX2 type. Mercury is not dissolved in hydrochloric or dilute sulfuric acid but does dissolve in aqua regia, nitric acid, and hot concentrated sulfuric acid.

Almost all Hg2+ salts have poor solubility in water. The nitrate Hg(N03)2, however, dissolves well.

The chlorides of mercury, Hg2Cl2 (calomel) and HgCl2 (corrosive sublimate), have great importance. Mercuric salts from hydrocyanic acid and thiocyanic acid are known, as is the mercury salt of fulminic acid—mercury fulminate, Hg(ONC)2. The action of ammonia on these mercury salts leads to the formation of a number of complexes, for example, HgCl-2NH3 (fusible white precipitate) and HgNH2Cl (non-fusible white precipitate). The organic mercury compounds have also found use.

Mercury is obtained by roasting ores or concentrates that contain mercury in the form of cinnabar:

HgS + 02 = Hg + SO2

The combustion gases pass through a dust-trapping chamber and enter a tube condenser made of stainless steel or Monel Metal; from here, liquid mercury descends into iron receivers. Purification is effected by passing the raw mercury as a thin stream through a tall vessel (1–1.5 m) of 10 percent nitric acid and by washing with water, drying, and distilling in a vacuum.

Mercury can also be obtained through a hydrometallurgical extraction from ores and concentrates. This process involves the displacement of mercury by aluminum from a solution of HgS in sodium sulfide. Methods have also been developed for obtaining mercury through the electrolysis of sulfide solutions.

Mercury is widely used in the production of such scientific instruments as barometers, thermometers, pressure gauges, vacuum pumps, normal cells, Polarographs, and capillary electrometers. It is also used in mercury-vapor lamps, switches, and rectifiers; it constitutes the liquid cathode in the production of alkali hydroxides and chlorine through electrolysis and is used as a catalyst in the synthesis of acetic acid. Mercury is used in the production of explosive substances and is employed in metallurgy for the amalgamation of gold and silver. There are a variety of uses for the element in medicine (calomel, corrosive sublimate, organic mercury compounds). Mercury is used as a pigment (cinnabar), as a herbicide and seed fungicide (organic mercury compounds), and as a component, designed to prevent the overgrowth of organisms, in the paints applied to ocean vessels. Mercury and its compounds are toxic; work with these substances therefore requires the observance of necessary safety measures.


Mercury in organisms. The content of mercury in organisms is approximately 10-6 percent. The average daily intake of mercury into the human body with food is 0.02–0.05 mg. The average concentration of mercury in human blood is 0.023 micrograms per milliliter μg/ml), and in urine, 0.1–0.2 μg/ml. With the pollution of water by industrial wastes, the concentration of mercury, mainly in the form of organic compounds, in crustaceans and fish may significantly exceed the level considered safe for human consumption. Mercury ions and compounds, in binding with the mercapto groups of enzymes, can deactivate the enzymes. Upon introduction into an organism, mercury affects the assimilation and metabolism of the trace elements Cu, Zn, Cd, and Se. On the whole, the biological role of mercury in organisms has not been adequately studied.


Mercury poisoning. Poisoning by mercury and mercury compounds can occur in mercury mines and factories and in the production of certain measuring instruments, lamps, pharmaceutical preparations, and insecticide-fungicides.

Mercury vapors present the greatest danger, and evaporation from an uncovered surface increases with the temperature of the air. Mercury that is inhaled is introduced into the blood, where it circulates and combines with proteins. It is deposited to some extent in the liver, kidneys, spleen, and brain tissues. Its toxic effect derives from blockage of the mercapto groups in fibrous proteins and interference with the activity of the brain, in particular the hypothalamus. Mercury is eliminated from the body through the kidneys, intestines, and sweat glands.

Acute mercury poisoning is rarely encountered. Chronic poisoning manifests itself through emotional disturbances, irritability, reduction in work capacity, interference with sleep, tremors of the fingers, reduction of the olfactory sense, and headaches. One symptom of mercury poisoning is a blue-black coloring at the edge of the gums; injury to the gums (atrophy, bleeding) can lead to gingivitis and stomatitis. Poisoning from the organic compounds of mercury (diethylmercuric phosphate, diethylmercury, and ethylmercuric chloride) is characterized by concurrent injuries to the central nervous system (en-cephalopolyneuritis), cardiovascular system, stomach, liver, and kidneys.

Mercury poisoning can be treated by intravenous injections of a 20-percent hyposulfite solution (from 12 to 15 injections over the course of the treatment) and by unithiol, pharmacologic and physiotherapeutic agents to normalize the increased nervous activity, and treatment at sanatoriums (Piatigorsk, Matsesta). Preventive measures include the replacement of mercury with less harmful substances, proper methods of storage, the observance of safety rules for the handling of mercury (hermetically sealed equipment, planned division of workrooms and working surfaces, proper ventilation), personal protection, and both preliminary and periodic medical examinations.

Preparations of mercury are used in medical practice mainly because of their antiseptic and diuretic properties. Mersalyl and chlormerodrin are used as diuretics. Mercury antiseptics include corrosive sublimate, which is used in disinfecting skin, clothes, and medical instruments, and diocid, which is used in sterilizing surgical instruments. Other antiseptics are mercuric cyanide and oxycyanide, used in bathing and syringing certain inflammations, mercuric ammonium chloride, used as an ointment for skin diseases, and yellow mercuric oxide, used as an ointment for skin and eye diseases. The mercury preparations previously used in the treatment of syphilis are not used in modern medicine. A. A. KASPAROV


Mel’nikov, S. M. “Rtut’.” In Kratkaia khimicheskaia entsiklopediia, vol. 4. Moscow, 1965.
Remy, H. Kurs neorganicheskoi khimii, vol. 2. Moscow, 1966. (Translated from German.)
Ripan, R., and J. Ceteanu. Neorganicheskaia khimiia. Moscow, 1972. (Translated from Rumanian.)
Nekrasov, B. V. Osnovy obshchei khimii, 2nd ed., vol. 2. Moscow, 1969.
Vrednye veshchestva v promyshlennosti, 6th ed. [part 2]. Editor in chief, N. V. Lazarev. Leningrad, 1971.
Trakhtenberg, I. M. Khronicheskoe vozdeistvie rtuti na organizm. Kiev, 1969.
Professional’nye bolezni, 3rd ed. Moscow, 1973.


A metallic element, symbol Hg, atomic number 80, atomic weight 200.59, existing at room temperature as a silvery, heavy liquid. Also known as quicksilver.


The planet nearest to the sun; it is visible to the naked eye shortly after sunset or before sunrise when it is nearest to its greatest angular distance from the sun.


god of thieves. [Gk. Myth.: Wheeler, 240]


1. a heavy silvery-white toxic liquid metallic element occurring principally in cinnabar: used in thermometers, barometers, mercury-vapour lamps, and dental amalgams. Symbol: Hg; atomic no.: 80; atomic wt.: 200.59; valency: 1 or 2; relative density: 13.546; melting pt.: --38.842?C; boiling pt.: 357?C
2. any plant of the euphorbiaceous genus Mercurialis


Roman myth the messenger of the gods


the second smallest planet and the nearest to the sun. Mean distance from sun: 57.9 million km; period of revolution around sun: 88 days; period of axial rotation: 59 days; diameter and mass: 38 and 5.4 per cent that of earth respectively
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