Callisto is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, the largest object in the Solar System not to be properly differentiated. Callisto was discovered in 1610 by Galileo Galilei. At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass, it is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1883000 km. It is not in an orbital resonance like the three other Galilean satellites—Io, Ganymede—and is thus not appreciably tidally heated. Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward, it is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt. Callisto is composed of equal amounts of rock and ices, with a density of about 1.83 g/cm3, the lowest density and surface gravity of Jupiter's major moons.
Compounds detected spectroscopically on the surface include water ice, carbon dioxide and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and a subsurface ocean of liquid water at depths greater than 100 km; the surface of Callisto is the oldest and most cratered in the Solar System. Its surface is covered with impact craters, it does not show any signatures of subsurface processes such as plate tectonics or volcanism, with no signs that geological activity in general has occurred, is thought to have evolved predominantly under the influence of impacts. Prominent surface features include multi-ring structures, variously shaped impact craters, chains of craters and associated scarps and deposits. At a small scale, the surface is varied and made up of small, sparkly frost deposits at the tips of high spots, surrounded by a low-lying, smooth blanket of dark material; this is thought to result from the sublimation-driven degradation of small landforms, supported by the general deficit of small impact craters and the presence of numerous small knobs, considered to be their remnants.
The absolute ages of the landforms are not known. Callisto is surrounded by an thin atmosphere composed of carbon dioxide and molecular oxygen, as well as by a rather intense ionosphere. Callisto is thought to have formed by slow accretion from the disk of the gas and dust that surrounded Jupiter after its formation. Callisto's gradual accretion and the lack of tidal heating meant that not enough heat was available for rapid differentiation; the slow convection in the interior of Callisto, which commenced soon after formation, led to partial differentiation and to the formation of a subsurface ocean at a depth of 100–150 km and a small, rocky core. The presence of an ocean within Callisto leaves open the possibility that it could harbor life. However, conditions are thought to be less favorable than on nearby Europa. Various space probes from Pioneers 10 and 11 to Galileo and Cassini have studied Callisto; because of its low radiation levels, Callisto has long been considered the most suitable place for a human base for future exploration of the Jovian system.
Callisto was discovered by Galileo in January 1610, along with the three other large Jovian moons—Ganymede, Io, Europa. Callisto is named after one of Zeus's many lovers in Greek mythology. Callisto was a nymph, associated with the goddess of the hunt, Artemis; the name was suggested by Simon Marius soon after Callisto's discovery. Marius attributed the suggestion to Johannes Kepler. However, the names of the Galilean satellites fell into disfavor for a considerable time, were not revived in common use until the mid-20th century. In much of the earlier astronomical literature, Callisto is referred to by its Roman numeral designation, a system introduced by Galileo, as Jupiter IV or as "the fourth satellite of Jupiter". In scientific writing, the adjectival form of the name is pronounced, or Callistan. Callisto is the outermost of the four Galilean moons of Jupiter, it orbits at a distance of 1 880 000 km. This is larger than the orbital radius—1 070 000 km—of the next-closest Galilean satellite, Ganymede.
As a result of this distant orbit, Callisto does not participate in the mean-motion resonance—in which the three inner Galilean satellites are locked—and never has. Like most other regular planetary moons, Callisto's rotation is locked to be synchronous with its orbit; the length of Callisto's day its orbital period, is about 16.7 Earth days. Its orbit is slightly eccentric and inclined to the Jovian equator, with the eccentricity and inclination changing quasi-periodically due to solar and planetary gravitational perturbations on a timescale of centuries; the ranges of change are 0.20 -- 0.60 °, respectively. These orbital variations cause the axial tilt to vary between 0.4 and 1.6°. The dynamical isolation of Callisto means that it has never been appreciably tidally heated, which has important consequences for its internal structure and evolution, its distance from Jupiter means that the charged-particle flux from Jupiter's magnetosphere at its surface is low—about 300 times lower than, for example, that at Europa.
Hence, unlike the other Galilean moons, charged-particle irradiation has had a minor effect on Callisto's surface. The radiation
A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet. In the Solar System there are six planetary satellite systems containing 185 known natural satellites. Four IAU-listed dwarf planets are known to have natural satellites: Pluto, Haumea and Eris; as of September 2018, there are 334 other minor planets known to have moons. The Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System. At 3,474 km across, the Moon is 0.27 times the diameter of Earth. The first known natural satellite was the Moon, but it was considered a "planet" until Copernicus' introduction of De revolutionibus orbium coelestium in 1543; until the discovery of the Galilean satellites in 1610, there was no opportunity for referring to such objects as a class. Galileo chose to refer to his discoveries as Planetæ, but discoverers chose other terms to distinguish them from the objects they orbited.
The first to use of the term satellite to describe orbiting bodies was the German astronomer Johannes Kepler in his pamphlet Narratio de Observatis a se quatuor Iouis satellitibus erronibus in 1610. He derived the term from the Latin word satelles, meaning "guard", "attendant", or "companion", because the satellites accompanied their primary planet in their journey through the heavens; the term satellite thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of "moon". In 1957, the launching of the artificial object Sputnik created a need for new terminology. Sputnik was created by Soviet Union, it was the first satellite ever; the terms man-made satellite and artificial moon were quickly abandoned in favor of the simpler satellite, as a consequence, the term has become linked with artificial objects flown in space – including, sometimes those not in orbit around a planet. Because of this shift in meaning, the term moon, which had continued to be used in a generic sense in works of popular science and in fiction, has regained respectability and is now used interchangeably with natural satellite in scientific articles.
When it is necessary to avoid both the ambiguity of confusion with Earth's natural satellite the Moon and the natural satellites of the other planets on the one hand, artificial satellites on the other, the term natural satellite is used. To further avoid ambiguity, the convention is to capitalize the word Moon when referring to Earth's natural satellite, but not when referring to other natural satellites. Many authors define "satellite" or "natural satellite" as orbiting some planet or minor planet, synonymous with "moon" – by such a definition all natural satellites are moons, but Earth and other planets are not satellites. A few recent authors define "moon" as "a satellite of a planet or minor planet", "planet" as "a satellite of a star" – such authors consider Earth as a "natural satellite of the sun". There is no established lower limit on what is considered a "moon"; every natural celestial body with an identified orbit around a planet of the Solar System, some as small as a kilometer across, has been considered a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets.
Small asteroid moons, such as Dactyl, have been called moonlets. The upper limit is vague. Two orbiting bodies are sometimes described as a double planet rather than satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon; some authors consider the Pluto–Charon system to be a double planet. The most common dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, because it depends on distance as well as relative mass; the natural satellites orbiting close to the planet on prograde, uninclined circular orbits are thought to have been formed out of the same collapsing region of the protoplanetary disk that created its primary. In contrast, irregular satellites are thought to be captured asteroids further fragmented by collisions. Most of the major natural satellites of the Solar System have regular orbits, while most of the small natural satellites have irregular orbits.
The Moon and Charon are exceptions among large bodies in that they are thought to have originated by the collision of two large proto-planetary objects. The material that would have been placed in orbit around the central body is predicted to have reaccreted to form one or more orbiting natural satellites; as opposed to planetary-sized bodies, asteroid moons are thought to form by this process. Triton is another exception; the capture of an asteroid from a heliocentric orbit is not always permanent. According to simulations, temporary satellites should be a common phenomenon; the only observed example is 2006 RH120, a temporary satellite of Earth for nine months in 2006 and 2007. Most regular moons (natural satellites following close and prograde orbits with small orb
Zeus is the sky and thunder god in ancient Greek religion, who rules as king of the gods of Mount Olympus. His name is cognate with the first element of his Roman equivalent Jupiter, his mythologies and powers are similar, though not identical, to those of Indo-European deities such as Jupiter, Perkūnas, Perun and Thor. Zeus is the child of Cronus and Rhea, the youngest of his siblings to be born, though sometimes reckoned the eldest as the others required disgorging from Cronus's stomach. In most traditions, he is married to Hera, by whom he is said to have fathered Ares and Hephaestus. At the oracle of Dodona, his consort was said to be Dione, by whom the Iliad states that he fathered Aphrodite. Zeus was infamous for his erotic escapades; these resulted in many divine and heroic offspring, including Athena, Artemis, Persephone, Perseus, Helen of Troy and the Muses. He was respected as an allfather, chief of the gods and assigned the others to their roles: "Even the gods who are not his natural children address him as Father, all the gods rise in his presence."
He was equated with many foreign weather gods, permitting Pausanias to observe "That Zeus is king in heaven is a saying common to all men". Zeus' symbols are the thunderbolt, eagle and oak. In addition to his Indo-European inheritance, the classical "cloud-gatherer" derives certain iconographic traits from the cultures of the ancient Near East, such as the scepter. Zeus is depicted by Greek artists in one of two poses: standing, striding forward with a thunderbolt leveled in his raised right hand, or seated in majesty; the god's name in the nominative is Ζεύς. It is inflected as follows: vocative: Ζεῦ. Diogenes Laërtius quotes Pherecydes of Syros as spelling the name, Ζάς. Zeus is the Greek continuation of *Di̯ēus, the name of the Proto-Indo-European god of the daytime sky called *Dyeus ph2tēr; the god is known under this name in the Rigveda, deriving from the root *dyeu-. Zeus is the only deity in the Olympic pantheon whose name has such a transparent Indo-European etymology; the earliest attested forms of the name are the Mycenaean Greek, di-we and, di-wo, written in the Linear B syllabic script.
Plato, in his Cratylus, gives a folk etymology of Zeus meaning "cause of life always to all things," because of puns between alternate titles of Zeus with the Greek words for life and "because of." This etymology, along with Plato's entire method of deriving etymologies, is not supported by modern scholarship. Cronus sired several children by Rhea: Hestia, Hera and Poseidon, but swallowed them all as soon as they were born, since he had learned from Gaia and Uranus that he was destined to be overthrown by his son as he had overthrown Uranus, his own father, an oracle that Rhea heard and wished to avert; when Zeus was about to be born, Rhea sought Gaia to devise a plan to save him, so that Cronus would get his retribution for his acts against Uranus and his own children. Rhea gave birth to Zeus in Crete, handing Cronus a rock wrapped in swaddling clothes, which he promptly swallowed. Varying versions of the story exist: According to Hyginus ) Zeus was raised by a nymph named Amalthea. Since Saturn ruled over the Earth, the heavens and the sea, she hid him by dangling him on a rope from a tree so he was suspended between earth and sky and thus, invisible to his father.
According to Pseudo-Apollodorus ) Zeus was raised by a goat named Amalthea in a cave called Dictaeon Antron. A a company of soldiers called Kouretes danced and clashed their spears against their shields so that Cronus would not hear the baby's cry. After reaching manhood, Zeus forced Cronus to disgorge first the stone his siblings in reverse order of swallowing. In some versions, Metis gave Cronus an emetic to force him to disgorge the babies, or Zeus cut Cronus's stomach open. Zeus released the brothers of Cronus, the Hecatonchires and the Cyclopes, from their dungeon in Tartarus, killing their guard, Campe; as a token of their appreciation, the Cyclopes gave him thunder and the thunderbolt, or lightning, hidden by Gaia. Together, his brothers and sisters and Cyclopes overthrew Cronus and the other Titans, in the combat called the Titanomachy; the defeated Titans were cast into a shadowy underworld region known as Tartarus. Atlas, one of the titans who fought against Zeus, was punished by having to hold up the sky.
After the battle with the Titans, Zeus shared the world with his elder brothers and Hades, by drawing lots: Zeus got the sky and air, Poseidon the waters, Hades the world of the dead. The ancient Earth, could not be claimed. Gaia resented. Soon after taking the throne as king of the gods, Zeus had to fight some of Gaia's other children, the monsters Typhon and Echidna, he left Echidna and her children alive. When Zeus was atop Mount Olympus he was appalled by human sac
In Greek mythology, Leda was an Aetolian princess who became a Spartan queen. Her myth gave rise to the popular motif in Renaissance and art of Leda and the Swan. Leda was the daughter of the Aetolian king Thestius hence she was called Thestias, her mother was either Leucippe or Deidameia, daughter of Perieres, or else Eurythemis, daughter of Cleoboea, or Laophonte, daughter of Pleuron. According to Alcman, Leda's parents were Glaucus and Laophonte while Eumelus attested that they are Sisyphus and Panteiduia or Paneidyia, she married king Tyndareus of Sparta and by him, mother of Helen of Troy and Castor and Pollux. Leda had other daughters by Tyndareus: Timandra and Philonoe. Leda was admired by Zeus; as a swan, Zeus fell into her arms for protection from a pursuing eagle. Their consummation, on the same night as Leda lay with her husband Tyndareus, resulted in two eggs from which hatched Helen and Castor and Pollux. Which children are the progeny of Tyndareus the mortal king, which are of Zeus and thus half-immortal, is not consistent among accounts, nor is which child hatched from which egg.
The split is always half mortal, half divine, although the pairings do not always reflect the children's heritage pairings. Castor and Pollux are sometimes both mortal, sometimes both divine. One consistent point is, it is always stated that Helen is the daughter of Zeus. In Homer's Iliad, Helen looks down from the walls of Troy and wonders why she does not see her brothers among the Achaeans; the narrator remarks that they are both dead and buried back in their homeland of Lacedaemon, thus suggesting that at least in the Homeric tradition, both were mortal. Another account of the myth states that Nemesis was the mother of Helen, was impregnated by Zeus in the guise of a swan. A shepherd found the egg and gave it to Leda, who kept it in a chest until the egg hatched; when the egg hatched, Leda adopted Helen as her daughter. Zeus commemorated the birth of Helen by creating the constellation Cygnus, the Swan, in the sky. Leda and the swan and Leda and the egg were popular subjects in ancient art. In the post-classical arts, it became a potent source of inspiration.
It is the subject of the Swan. She is the main subject in Honoré Desmond Sharrer's "Leda & the Folks", a large painting focusing as well on the parents of entertainer Elvis Presley and located at the Smith College Museum of Art. March, J.. Cassell's Dictionary Of Classical Mythology. London. ISBN 0-304-35161-X. Peck, H.. Harper's Dictionary of Classical Antiquities. Media related to Leda at Wikimedia Commons Warburg Institute Iconographic Database
Fire Maidens from Outer Space
Fire Maidens from Outer Space, released in the United States as Fire Maidens of Outer Space, is an 80-minute black-and-white science fiction feature film. It was a British production, written and directed by American filmmaker Cy Roth as a collaboration between Cy Roth Productions and Criterion Films, distributed in the UK by Eros Films and in the USA by Topaz Film Co.. The film stars Anthony Dexter as the lead astronaut, Susan Shaw as a "fire maiden" who befriends him, Paul Carpenter as the expedition captain, Jacqueline Curtis as the "fire maiden" leader. There were 13 additional "fire maidens"; the music score features. Many film critics have dubbed the film the "worst movie made"; the discovery of signs of life on the 13th moon of Jupiter leads to the sending of a crew of five chain-smoking male astronauts, armed with handguns, to investigate. On the moon, they rescue Hestia, a beautiful girl, being attacked by a monster, they subsequently discover a colony of the original Atlantis. There are only seventeen people left, all women save for a single middle-aged man, the girls' "father".
Prasus hopes the spacemen will stay and help him destroy the monster, a slender, male hominid creature, around six feet tall with dark, pitted skin, impervious to bullets, described as a "man with the head of a beast". Duessa, the leader of the women, determines to hold them captive to use as mates; the monster lurks outside the city's walls, but breaks into the city and kills Prasus along with several of the women, including Duessa. It is killed by the earthmen, the remaining women decide to let them return to earth. Hestia returns with them, the astronauts promise to send spaceships back with husbands for the rest; the Monthly Film Bulletin review credits Lito Carruthers as editor, Scott MacGregor as assistant director. Although MacGregor is credited onscreen as production and art supervisor, John Pellatt receives screen credit as assistant director; the anonymous actor playing the creature wears dark, tight-fitting clothing with visible zippers. Carruthers' contribution to the film has not been confirmed.
Fire Maidens from Outer Space was released in 1956. In a contemporary review, The Monthly Film Bulletin stated that "Even the most dedicated connoisseurs of the artless are to find this British attempt at science-fiction something of a strain on their patience."From retrospective reviews, Halliwell's Film and Video Guide describes the film as "a strong contender for the title of the worst movie made, with diaphanously clad English gals striking embarrassed poses against cardboard sets". In Phil Hardy's book Science Fiction, a review described the film as "a bottom-of-the barrel piece of British Science Fiction", that "the film's one claim to fame is its extensive use of classical music as background music, a trick that Stanley Kubrick deployed with far more aplomb in 2001 - A Space Odyssey"; the DVD Talk website stated Fire Maidens from Outer Space "may be among the worst-ever professionally produced science fiction films" In November 1992, Fire Maidens of Outer Space was featured as an episode of movie-mocking television show Mystery Science Theater 3000.
List of films considered the worst Fire Maidens from Outer Space on IMDb Fire Maidens from Outer Space at Trailers from Hell
Leda is a large, dark main-belt asteroid, discovered by French astronomer J. Chacornac on January 12, 1856, named after Leda, the mother of Helen of Troy in Greek mythology. In the Tholen classification system, it is categorized as a carbonaceous C-type asteroid, while the Bus asteroid taxonomy system lists it as a Cgh asteroid; the spectra of the asteroid displays evidence of aqueous alteration. Leda has been studied by radar. During 2002, 38 Leda was observed by radar from the Arecibo Observatory; the return signal matched an effective diameter of 116 ± 13 km. This is consistent with the asteroid dimensions computed through other means. Based upon a light curve, generated from photometric observations of this asteroid at Pulkovo Observatory, it has a rotation period of 12.834 ± 0.001 hours and varies in brightness by 0.15 ± 0.01 in magnitude. JPL Ephemeris 38 Leda at the JPL Small-Body Database Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters
Mass is both a property of a physical body and a measure of its resistance to acceleration when a net force is applied. The object's mass determines the strength of its gravitational attraction to other bodies; the basic SI unit of mass is the kilogram. In physics, mass is not the same as weight though mass is determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass; this is because weight is a force, while mass is the property that determines the strength of this force. There are several distinct phenomena. Although some theorists have speculated that some of these phenomena could be independent of each other, current experiments have found no difference in results regardless of how it is measured: Inertial mass measures an object's resistance to being accelerated by a force. Active gravitational mass measures the gravitational force exerted by an object.
Passive gravitational mass measures the gravitational force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force; the inertia and the inertial mass describe the same properties of physical bodies at the qualitative and quantitative level by other words, the mass quantitatively describes the inertia. According to Newton's second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A body's mass determines the degree to which it generates or is affected by a gravitational field. If a first body of mass mA is placed at a distance r from a second body of mass mB, each body is subject to an attractive force Fg = GmAmB/r2, where G = 6.67×10−11 N kg−2 m2 is the "universal gravitational constant". This is sometimes referred to as gravitational mass. Repeated experiments since the 17th century have demonstrated that inertial and gravitational mass are identical.
The standard International System of Units unit of mass is the kilogram. The kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. However, because precise measurement of a decimeter of water at the proper temperature and pressure was difficult, in 1889 the kilogram was redefined as the mass of the international prototype kilogram of cast iron, thus became independent of the meter and the properties of water. However, the mass of the international prototype and its identical national copies have been found to be drifting over time, it is expected that the re-definition of the kilogram and several other units will occur on May 20, 2019, following a final vote by the CGPM in November 2018. The new definition will use only invariant quantities of nature: the speed of light, the caesium hyperfine frequency, the Planck constant. Other units are accepted for use in SI: the tonne is equal to 1000 kg. the electronvolt is a unit of energy, but because of the mass–energy equivalence it can be converted to a unit of mass, is used like one.
In this context, the mass has units of eV/c2. The electronvolt and its multiples, such as the MeV, are used in particle physics; the atomic mass unit is 1/12 of the mass of a carbon-12 atom 1.66×10−27 kg. The atomic mass unit is convenient for expressing the masses of molecules. Outside the SI system, other units of mass include: the slug is an Imperial unit of mass; the pound is a unit of both mass and force, used in the United States. In scientific contexts where pound and pound need to be distinguished, SI units are used instead; the Planck mass is the maximum mass of point particles. It is used in particle physics; the solar mass is defined as the mass of the Sun. It is used in astronomy to compare large masses such as stars or galaxies; the mass of a small particle may be identified by its inverse Compton wavelength. The mass of a large star or black hole may be identified with its Schwarzschild radius. In physical science, one may distinguish conceptually between at least seven different aspects of mass, or seven physical notions that involve the concept of mass.
Every experiment to date has shown these seven values to be proportional, in some cases equal, this proportionality gives rise to the abstract concept of mass. There are a number of ways mass can be measured or operationally defined: Inertial mass is a measure of an object's resistance to acceleration when a force is applied, it is determined by applying a force to an object and measuring the acceleration that results from that force. An object with small inertial mass will accelerate more than an object with large inertial mass when acted upon by the same force. One says. Active gravitational mass is a measure of the strength of an object's gravitational flux. Gravitational field can be measured by allowing a small "test object" to fall and measuring its free-fall acceleration. For example, an object in free fall near the Moon is subject to a smaller gravitational field, hence