Health & Medicine

Mind & Brain

Plants & Animals

Earth & Climate

Space & Time

• Astronomy
• Black Holes
• Cosmic Rays
• Dark Matter
• Extrasolar Planets
• Galaxies
• Nebulae
• Stars

• Astrophysics
• Big Bang
• Cosmology

• Asteroids, Comets and Meteors
• Jupiter
• Kuiper Belt
• Mars
• Mercury
• Moon
• Neptune
• Northern Lights
• Pluto
• Saturn
• Solar System
• Sun
• Uranus
• Venus
• Xena

• ESA
• NASA
• Satellites
• Space Exploration
• Space Missions
• Space Probes
• Space Station
• Space Telescopes

Matter & Energy

Computers & Math

Fossils & Ruins

Saturn -- Saturn is the sixth planet from the Sun. It is a gas giant, the second-largest planet in the solar system after Jupiter. Saturn has a prominent system of rings, consisting of mostly ice particles ... > full article

Titan (moon) -- Titan, or Saturn VI, is the largest moon of Saturn and the second largest moon in the solar system, after Jupiter's moon Ganymede. It is roughly 50% larger than Earth's moon by diameter, and is ... > full article

Saturn's natural satellites -- Saturn is currently known to have 56 moons, many of which were discovered very recently, and 3 additional un-confirmed, hypothetical moons. However, a precise number of moons can never be given, as ... > full article

Neptune's natural satellites -- Neptune has 13 known moons. The largest by far is Triton, discovered by William Lassell just 17 days after the discovery of Neptune itself. It took a hundred years to discover the second, Nereid. ... > full article

Uranus' natural satellites -- Uranus has 27 known moons. The first two moons (Titania and Oberon) were discovered by William Herschel on March 13, 1787. Two more moons (Ariel and Umbriel) were discovered by William Lassell in ... > full article

Dysnomia (moon of Eris) -- Dysnomia, is a moon of the dwarf planet Eris. The satellite is about 60 times fainter than Eris, and its diameter is estimated to be approximately eight times smaller. Astronomers now know that three ... > full article

Gas giant -- A gas giant is a large planet that is not primarily composed of rock or other solid matter. Gas giants may have a rocky or metallic core—in fact, such a core is thought to be required for a gas giant ... > full article

Equatorial bulge -- An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid. Because of a planet's equatorial bulge, its ... > full article

Multistage rocket -- A multistage (or multi-stage) rocket is, like any rocket, propelled by the recoil pressure of the burning gases it emits as it burns fuel. What characterizes it as "multi-stage" is that it ... > full article

Neptune -- Neptune is the eighth and outermost planet in our solar system. It is the fourth-largest planet by diameter and the third-largest by mass; Neptune is 17 times the mass of Earth and is slightly more ... > full article

Jupiter -- Jupiter is the fifth planet from the Sun and by far the largest within the solar system. Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon and Venus); however at ... > full article

Volcano -- A volcano is an opening (or rupture) in the Earth's surface or crust, which allows hot, molten rock, ash, and gases to escape from deep below the surface. Volcanic activity involving the extrusion of ... > full article

Definition of planet -- The definition of "planet" has for some time been the subject of intense debate. Although the word dates back thousands of years, no officially decreed scientific definition of "planet" existed ... > full article

Deimos (moon) -- Deimos is probably an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars, though this hypothesis is still in some dispute. Like most bodies of its size, ... > full article

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. Despite popular imagery, the ... > full article

Uranus -- Uranus is the seventh planet from the Sun. It is a gas giant, the third largest by diameter and fourth largest by mass. NASA's Voyager 2 is the only spacecraft to have visited the planet and no other ... > full article

Solar system -- The Solar System comprises the Sun and the retinue of celestial objects gravitationally bound to it: the eight planets, their 162 known moons, three currently identified dwarf planets and their four ... > full article

Impact crater -- An impact crater is a circular depression on a surface, usually referring to a planet, moon, asteroid, or other celestial body, caused by a collision of a smaller body (meteor) with the ... > full article

Planet -- The International Astronomical Union defines "planet" as a celestial body that, within the Solar System that is in orbit around the Sun; has sufficient mass for its self-gravity to overcome rigid ... > full article

NASA -- The National Aeronautics and Space Administration (NASA), which was established in 1958, is the agency responsible for the public space program of the United States of America. NASA's vision is "to ... > full article