Solar System
Saturn
The Planet Saturn -- in astronomy, 6th planet from the sun. Astronomical and Physical Characteristics of Saturn Saturn�s orbit lies between those of Jupiter and Uranus; its mean distance from the sun is c.886 million mi (1.43 billion km), ...
Saturn's Moon Pan
Saturn's moon Pan -- Pan, the innermost known satellite, was found from photographs taken by Voyager during its encounter with Saturn. It was discovered by Mark R. Showalter in 1990, 9 years after the Voyager encounter. Pan is located 133,583 k...
Saturn's Moon Atlas
Saturn's moon Atlas -- Atlas, the second of Saturn's known satellites, orbits near the outer edge of the A-ring and is about 40 by 20 kilometers (25 by 15 miles) in size. It is probably a shepherd satellite for Saturn's A-ring. Atlas was discov...
Saturn's Moon Prometheus
Saturn's moon Prometheus -- Prometheus [pra-MEE-thee-us] is the third of Saturn's known satellites. It was discovered from photographs taken by Voyager during its encounter with Saturn by S. Collins and others. Prometheus acts as a shepherd satelli...
Saturn's Moon Pandora
Saturn's moon Pandora -- Pandora [pan-DOR-uh] is the fourth of Saturn's known satellites. It was discovered from photographs taken by Voyager during its encounter with Saturn by S. Collins and others. Pandora is the outer shepherd satellite for ...
Saturn's Moon Epimetheus
Saturn's moon Epimetheus -- Epimetheus is a moon of Saturn that was probably first observed by Walker and Audouin Dollfus in 1966 when they discovered Janus, but the situation was confused since Janus is in a very similar orbit and so Walker officially...
Saturn's Moon Janus
Saturn's moon Janus -- Janus is a moon of Saturn discovered by the French astronomer Audouin Dollfus in 1966. Dollfus is credited with the discovery of Janus but it's not really certain whether the object he saw was Janus or Epimetheus and his obse...
Saturn's Moon Mimas
Saturn's moon Mimas -- Mimas is a moon of Saturn that was discovered in 1789 by William Herschel. Mimas' low density (1.17) indicates that it is composed mostly of water ice with only a small amount of rock. Mimas' most distinctive feature is a col...
Saturn's Moon Enceladus
Saturn's moon Enceladus -- Enceladus is a moon of Saturn discovered in 1789 by William Herschel. At least five different types of terrain have been identified on Enceladus. In addition to craters there are smooth plains and extensive linear cracks ...
Saturn's Moon Tethys
Saturn's moon Tethys -- Tethys is a moon of Saturn that was discovered by Giovanni Cassini in 1684. Tethys is an icy body similar in nature to Dione and Rhea. The density of Tethys is 1.21 g/cm3, indicating that it is composed almost entirely of wa...
Saturn's Moon Telesto
Saturn's moon Telesto -- In Greek mythology, Telesto ("success") was a daughter of Oceanus and Tethys. Alternative: Telestho Telesto is a moon of Saturn, discovered by Smith, Reitsema, Larson and Fountain in 1980 from ground-based observations....
Saturn's Moon Calypso
Saturn's moon Calypso -- Calypso is a moon of Saturn discovered by Pascu, Seidelmann, Baum and Currie in 1980 from ground-based observations. Calypso is co-orbital with the moon Tethys, and resides in Tethys' trailing Lagrangian point (L5). The...
Saturn's Moon Dione
Saturn's moon Dione -- Dione is a moon of Saturn discovered by Giovanni Cassini in 1684. It is composed primarily of water ice, but as the densest of Saturn's moons (aside from Titan, whose density is increased by gravitational compression) it must hav...
Saturn's Moon Helene
Saturn's moon Helene -- Helene is a moon of Saturn, discovered by Laques and Lecacheux in 1980 from ground-based observations. It is co-oribtal with Dione and located in its leading Lagrangian point (L4) and hence is sometimes referred to as "Dione...
Saturn's Moon Rhea
Saturn's moon Rhea -- Rhea is the second largest moon of Saturn. It was discovered in 1672 by Giovanni Cassini. Rhea is an icy body with a density of about 1.24 gm/cm3. This low density indicates that it has a rocky core taking up less than one-thi...
Saturn's Moon Titan
Saturn's moon Titan -- Titan is the planet Saturn's largest moon. It is larger than either of the planets Mercury or Pluto and is the second-largest moon in the solar system after Ganymede (it was originally thought to be slightly larger than Ganymede,...
Saturn's Moon Hyperion
Saturn's moon Hyperion -- Hyperion is a moon of Saturn discovered by Bond and Lassell in 1848. It is the largest highly irregular (non-spherical) body in the solar system (Proteus is quite a bit larger but is almost spherical). It seems likely that...
Saturn's Moon Iapetus
Saturn's moon Iapetus -- Iapetus is the third-largest moon of Saturn, discovered by Giovanni Cassini in 1671. Its density is similar to that of Rhea, indicating that it has a small amount of rocky materials. Its leading side is dark (albedo 0.03-0....
Saturn's Moon Phoebe
Saturn's moon Phoebe -- Phoebe is the outermost of Saturn's known moons. Phoebe is almost 4 times more distant from Saturn than its nearest neighbor (Iapetus). It was discovered by William Henry Pickering in 1898. Most of Saturn's moons have very b...
Uranus
Uranus -- Uranus is the seventh planet from the sun. It is a gas giant. Physical characteristics Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium (in contrast to Jupiter and Saturn which a...
Uranus' Moon Cordelia
Uranus' moon Cordelia -- Cordelia is the innermost moon of Uranus. Apart from its orbital radius and dimensions, virtually nothing is known about it. It takes its name from the youngest daughter of Lear in William Shakespeare's King Lear. Cord...
Uranus' Moon Ophelia
Uranus' moon Ophelia -- Ophelia is a moon of Uranus. It was named after the daughter of Polonius in William Shakespeare's play Hamlet. Ophelia acts as the outer shepherd satellite for Uranus' epsilon planetary ring. Its orbit is within Uranus' syn...
Uranus' Moon Bianca
Uranus' moon Bianca -- Bianca is a moon of Uranus. It was named after the sister of Katherine in Shakespeare's play The Taming of the Shrew. Other than its orbit and size, virtually nothing is known about it. ----- Discovery Discovered ...
Uranus' Moon Cressida
Uranus' moon Cressida -- Cressida is a moon of Uranus. It was named after the daughter of Calchas in William Shakespeare's play Troilus and Cressida. Other than its size and orbit, virtually nothing is known about it. ----- Discovery Di...
Uranus' Moon Desdemona
Uranus' moon Desdemona -- Desdemona is a moon of Uranus. It is named after the wife of Othello in William Shakespeare's play Othello. Other than its size and orbit, virtually nothing is known about it. ----- Discovery Discovered by Voya...
Uranus' Moon Juliet
Uranus' moon Juliet -- Juliet is a moon of Uranus. It was named after the heroine in William Shakespeare's play Romeo and Juliet. Other than its size and orbit, virtually nothing is known about it. ----- Discovery Discovered by Voyager ...
Uranus' Moon Portia
Uranus' moon Portia -- Portia is a moon of Uranus, named after the 2 two heroines in plays by William Shakespeare. It was discovered in 1986 by Voyager 2. Very little is known about it. Since it is below Uranus' synchronous orbit radius, Portia's ...
Uranus' Moon Rosalind
Uranus' moon Rosalind -- Rosalind is a moon of Uranus. It was named after the daughter of the banished Duke in William Shakespeare's play As You Like It. Other than its size and orbit, virtually nothing is known about it. ----- Discovery ...
Uranus' Moon Belinda
Uranus' moon Belinda -- Belinda is a moon of Uranus. It was named after the heroine in Alexander Pope's The Rape of the Lock. Other than its size and orbit, virtually nothing is known about it. ----- Discovery Discovered by Voyager 2 Di...
Uranus' Moon Puck
Uranus' moon Puck -- Puck is a moon of Uranus. It was discovered by Voyager 2 in 1986. Little is known about it aside from its orbit, its size, and its dark albedo (approximately 0.07). In Celtic mythology and English folklore, Puck is a mischievo...
Uranus' Moon Miranda
Uranus' moon Miranda -- Miranda is the smallest and innermost of Uranus' major moons. Discovered in 1948 by Gerard Kuiper, it roughly half water ice with the remainder being divided between silicate rock and methane-related organic compounds. Mira...
Uranus' Moon Ariel
Uranus' moon Ariel -- Ariel is a moon of Uranus discovered in 1851 by William Lassell. Its composition is roughly 50% water ice, 30% silicate rock, and 20% methane ice, and it appears to have regions of fresh frost in places. Largely devoid of...
Uranus' Moon Umbriel
Uranus' moon Umbriel -- Umbriel is a moon of Uranus discovered in 1851 by William Lassell. It was named after the 'dusky melancholy sprite' in Alexander Pope's The Rape of the Lock. Umbriel's surface is the darkest of the Uranian moons, and it is a...
Uranus' Moon Titania
Uranus' moon Titania -- Titania is the largest moon of Uranus. Titania was discovered on January 11, 1787 by William Herschel. All of the moons of Uranus are named for characters from Shakespeare or Alexander Pope. Names for the first four discove...
Uranus' Moon Oberon
Uranus' moon Oberon -- Oberon is the name of the outermost of the major moons of the planet Uranus; discovered on January 11, 1787 by William Herschel. All of the moons of Uranus are named for characters from Shakespeare or Alexander Pope. Names f...
Uranus' Moon Caliban
Uranus' moon Caliban -- Caliban is a moon of Uranus, named after Caliban, the character in William Shakespeare's play The Tempest. Caliban was discovered on September 6 - September 7, 1997 by Brett Gladman, Phil Nicholson, Joseph Burns, and JJ Kav...
Uranus' Moon Sycorax
Uranus' moon Sycorax -- Sycorax is a moon of Uranus. It was named after a witch living on an island in William Shakespeare's play The Tempest. Its orbital radius is approximately 12.2 million km from Uranus and is about 160 km in diameter, but thi...
Neptune
Planet Neptune -- Neptune is the eighth planet from the sun. It is a gas giant. Orbiting so far from the sun, Neptune receives very little heat. Its 'surface' temperature is -218 degrees Celsius (below zero). However, the planet seems to have an i...
Neptune's Moon Naiad
Planet Naiad -- A moon of Neptune, Naiad is named after the Naiads of Greek legend. Naid was the last of the satellites discovered in 1989 by Voyager 2. It is irregularly shaped and shows no sign of any geological modification. Since its orbit...
Neptune's Moon Thalassa
Planet Thalassa -- Thalassa is the second moon of Neptune. Thalassa was named after a daughter of Aether and Hemera from Greek mythology. "Thalassa" is also the Greek word for "sea". It was discovered in 1989 by Voyager 2. It is irregularly shaped...
Neptune's Moon Despina
Planet Despina -- Despina is the third known moon of Neptune. It was discovered in 1989 by Voyager 2, and very little is known about it. It is irregularly shaped and shows no sign of any geological modification. Since its orbit is below Neptun...
Neptune's Moon Galatea
Planet Galatea -- Galatea is the fourth known moon of Neptune, named after the the Nereid of Greek legend. It was discovered in 1989 by Voyager 2 and very little is known about it. It is irregularly shaped and shows no sign of any geological modif...
Neptune's Moon Larissa
Planet Larissa -- Larissa is the fifth of Neptune's known moons. It was discovered by Harold Reitsema based on ground-based stellar occultation observations, and was photographed by Voyager 2 in 1989. Larissa is irregular (non-spherical) in shape ...
Neptune's Moon Proteus
Planet Proteus -- Proteus is one of Neptune's moons. It is one of the darkest objects in the solar system, as dark as soot; like Saturn's moon Phoebe, it reflects only 6 percent of the sunlight that strikes it. Proteus is about 400 kilometers in d...
Neptune's Moon Triton
Planet Triton -- Triton is the planet Neptune's largest moon, discovered by William Lassell in 1846 just 17 days after the planet itself was discovered. It is named after Triton, from Greek mythology. Triton is unique among all large moons in ...
Neptune's Moon Nereid
Planet Nereid -- Nereid ("NEER ee ed") is the outermost of Neptune's known moons and the third largest, with a diameter of 340 km. Its orbit averages 5,513,400 km in radius, but is highly eccentric and varies from 1,353,600 to 9,623,700 kilometers...
Pluto
Planet Pluto -- Pluto is the ninth and smallest planet of our solar system. It was discovered by the astronomer Clyde Tombaugh at the Lowell Observatory in Arizona on February 18, 1930 (although the body was first photographed on March 19, 1915). ...
Pluto's Moon Charon
Planet Charon -- Charon is the only known satellite of Pluto. Charon was discovered by astronomer James Christy in 1978 using photographic plates which showed a bulge moving around Pluto. Christy named it after the Greek mythological figure Charon...
Asteroid Belt
Asteroid Belt -- The Asteroid belt is a region of the solar system falling roughly between the planets Mars and Jupiter where the greatest concentration of asteroid orbits can be found. It is believed that, during the first million years of the sol...
Kuiper Belt
Kuiper Belt -- The Kuiper belt is an area of the solar system extending outwards from the orbit of Neptune (at 30 AU) to 50 AU. The largest of the objects in the Kuiper belt are the planet Pluto and its moon Charon. A new Kuiper belt object, curren...
Leonids Meteor Shower
Leonids Meteor Shower -- The Leonids are a prolific meteor shower associated with the comet Tempel-Tuttle. The meteor stream is viewable every year around November 17 and is thought to be comprised of particles ejected by the comet as it passes by ...
Lunar Eclipse
Lunar eclipse -- From Earth, a lunar eclipse occurs when Sun, Earth and Moon are in a single line with Earth in the middle. If this occurs, the Moon (or part of it) does not receive light from the Sun because it is in the shadow of the Earth, and t...
Lunar Phase
Lunar Phase -- The lunar phase is an astronomical term referring to the portion of the Moon that is visibly illuminated by the Sun, as seen from Earth. As the Moon orbits the Earth, the relative positions of the Sun, Earth and Moon change. Since th...
Moon
The Moon -- The Moon is the largest satellite of the Earth, and is occasionally called Luna (Latin for moon) to distinguish it from the general use of the word "moon". The Moon is distinguished from the satellites of other planets by its initial ca...
Olympus Mons
Olympus Mons -- Olympus Mons is the tallest mountain in the solar system, at 25 km. Located on Mars, and officially called by its Latin name Olympus Mons. It is named for the mountain on Earth. Olympus Mons is an apparently extinct shield volcano, ...
Oort Cloud
Oort Cloud -- The Oort cloud is a postulated cloud of comets situated about 50,000 to 100,000 AU from the sun. Although no direct observations have been made of such a cloud, it is believed to be the source of most or all comets entering the inner ...
Perseids Meteor Shower
Perseids Meteor Shower -- Like most meteor showers, the Perseids are caused by comet debris. As comets enter the inner solar system, they are warmed by the sun and peppered by the solar wind, which produces the familar tails that stretch across the...
Quaoar
Quaoar -- Quaoar ("kwah-oh-ahr", /kwA o Ar/) is a Trans-Neptunian object circling the Sun in the Kuiper belt, discovered in 2002 by astronomers Chad Trujillo and Mike Brown at the California Institute of Technology in Pasadena, California. Quaoar i...
Sunspot
Sunspot -- A sunspot is a region on the Sun's surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. Although they are blindingly bright, at temperatures of roughly 5000 Kelvin, the contras...
Solar Eclipse
Solar Eclipse -- A solar eclipse occurs when Sun, Moon and Earth are on a single line, the Moon being in the middle. Seen from the Earth, the Moon is in front of the Sun and thus part or all of the light of the Sun is hidden by the Moon. Thus it may se...
Solar Flare
Solar Flare -- A solar flare is a violent eruption that explodes from a star's photosphere with energies equivalent to tens of millions of hydrogen bombs. Solar flares from the Sun send out a streams of highly energetic solar wind that can present ...
Solar Maximum
Solar Maximum -- The Sun, a roiling ball of plasma, occupies its place in space approximately 93 million miles from Earth. Though it seems simple to inhabitants of this planet -- the Sun shines, giving light and heat -- the processes occurring in t...
Solar Prominence
Solar Prominence -- Solar prominences are large arch-shaped structures observable in the solar corona. These often have a twist and occasionally become unstable, ejecting plasma and magnetic flux out from the sun. The physics of solar prominence in...
Solar Radiation
Solar Radiation -- Solar radiation is radiant energy emitted by the sun due to nuclear fusion reactions. Fusion is the process whereby stars produce huge quantities of energy from the fusion of hydrogen or helium, in one of the most efficient proce...
Solar System
Solar System -- The Solar System consists of the Sun and its associated objects and phenomena, including the Earth, the planet on which we live. It is the best-known example of a planetary system, which more generally is composed of one or more sta...
Solar Wind
Solar Wind -- Solar wind, a stream of particles (mostly high-energy protons ~ 500 Kev) that is continually ejected from the surface of the Sun. The composition of this plasma is identical to the Sun's corona, 73% hydrogen and 25% helium with the re...
Van Allen Radiation Belt
Van Allen Radiation Belt -- The Van Allen radiation belt is a torus of energetic charged particles around Earth, trapped by Earth's magnetic field. The presence of a radiation belt had been theorized prior to the Space Age and the belt's presence w...
Earth's Moon
The Moon -- natural satellite of a planet, in particular, the single natural satellite of the earth. The Earth-Moon System The moon is the earth�s nearest neighbor in space. In addition to its proximity, the moon is also exceptional in t...
Mars' Moon -- Phobos
Mars' Moon Phobos -- in astronomy, innermost moon, or natural satellite, of Mars. Phobos orbits Mars at a distance of only 9,378 km (5,627 mi), closer to its planet than any other moon in the solar system. In fact, it is so close that the force of ...
Mars' Moon -- Deimos
Mars' Moon Deimos -- outermost of two small moons orbiting the planet Mars. Deimos orbits Mars at a distance of about 23,500 km (about 14,100 mi), completing an orbit once every 1.26 Earth days. The moon's orbit is almost circular and is only slightly ...
Earth
Earth -- in geology and astronomy, fifth largest planet of the solar system and the only planet definitely known to support life. Gravitational forces have molded the earth, like all celestial bodies, into a spherical shape. However, the earth is n...
Mars
The Planet Mars -- in astronomy, 4th planet from the sun, with an orbit next in order beyond that of the earth. Physical Characteristics Mars has a striking red appearance, and in its most favorable position for viewing, when it is opposite th...
Mercury
The Planet 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 abou...
Venus
The Planet Venus -- in astronomy, 2d planet from the sun; it is often called the evening star or morning star and is brighter than any object in the sky except the sun and the moon. Because its orbit lies between the sun and the orbit of the earth,...
The Sun
The Sun -- intensely hot, self-luminous body of gases at the center of the solar system. Its gravitational attraction maintains the planets, comets, and other bodies of the solar system in their orbits. The sun is actually a star of about medium si...
Jupiter
Jupiter -- in astronomy, fifth planet from the sun and largest planet of the solar system. Astronomical and Physical Characteristics Jupiter�s orbit lies beyond the asteroid belt at a mean distance of 483.6 million mi (778.3 million km) ...
Jupiter's Moon Metis
Jupiter's moon Metis -- Metis [MEE-tis] is the innermost known satellite of Jupiter. It was named after a Titaness who was a consort of Zeus (Jupiter). Metis and Adrastea lie within Jupiter's main ring and may be the source of material for the ring...
Jupiter's Moon Adrastea
Jupiter's Moon Adrastea -- Adrastea [a-DRAS-tee-uh] is the second innermost known satellite of Jupiter. Adrastea was the daughter of Jupiter and Ananke and the distributor of rewards and punishments. Adrastea and Metis lie within Jupiter's main rin...
Jupiter's Moon Amalthea
Jupiter's Moon Amalthea -- Amalthea [am-al-THEE-uh] is one of Jupiter's smaller moons. It was named after the nymph who nursed the infant Jupiter with goats milk. It was discovered in 1892 by the American astronomer Edward Emerson Barnard while mak...
Jupiter's Moon Thebe
Jupiter's Moon Thebe -- Thebe [THEE-bee] is the fourth known satellite of Jupiter. Thebe was a nymph and the daughter of the river god Asopus. Thebe rotates synchronously around Jupiter. Very little is known about this moon. Discovered by Stephe...
Jupiter's Moon Io
Jupiter's Moon Io -- Looking like a giant pizza covered with melted cheese and splotches of tomato and ripe olives, Io is the most volcanically active body in the solar system. Volcanic plumes rise 300 kilometers (190 miles) above the surface, with mat...
Jupiter's Moon Europa
Jupiter's Moon Europa -- Europa is a puzzle. The sixth largest moon in our Solar System, Europa confounds and intrigues scientists. Few bodies in the Solar System have attracted as much scientific attention as this moon of Jupiter because of its possib...
Jupiter's Moon Ganymede
Jupiter's Moon Ganymede -- Ganymede is the largest satellite in the solar system with a diameter of 5,268 km (3270 miles). It is larger than Mercury and Pluto, and three-quarters the size of Mars. If Ganymede orbited the Sun instead of orbiting Jupiter...
Jupiter's Moon Callisto
Jupiter's Moon Callisto -- With a diameter of over 4,800 km (2,985 miles), Callisto is the third largest satellite in the solar system and is almost the size of Mercury. Callisto is the outermost of the Galilean satellites, and orbits beyonds Jupiter's...
Jupiter's Moon Leda
Jupiter's Moon Leda -- Leda ("LEE duh") is the ninth of Jupiter's known satellites and the smallest. Discovered by C. Kowal Date of discovery 1974 Mass (kg) 5.68e+15 Mass (Earth = 1) 9.5047e-10 Equatorial radius (km) 8 Equatorial radius (Earth...
Jupiter's Moon Himalia
Jupiter's Moon Himalia -- Himalia is Jupiter's tenth moon. Himalia is 110 miles (170 km) in diameter and orbits 7,000,000 miles (11,480,000 km) from Jupiter. Himalia has a mass of 9.5 x 1018kg. It orbits Jupiter in 250.5662 (Earth) days. Very l...