Planetary science Reference Libraries

Page 2 of about 52 Articles
2004-10-19 04:45:44

Sky -- Although almost everyone have seen it, sky is hard to be defined precisely. Generally, sky is the space seen when one looks upward from the surface of a planet. Some people define sky as the denser gaseous zone of a planet's atmosphere. Clouds, rainbows and weather all occur amongst a planet's sky. In astronomy, the sky is divided into many regions, called constellations. The...

Ring Current
2004-10-19 04:45:44

Ring Current -- A ring current is an electric current carried by charged particles trapped in a planet's magnetosphere. It is caused by the longitudinal drift of energetic (10-200 keV) particles. Earth's Ring Current Earth's ring current is responsible for geomagnetic storms. The ring current system consists of a band, at a distance of 3-5 RE(1), which lies in the equatorial plane and...

Retrograde Motion
2004-10-19 04:45:44

Retrograde Motion -- Retrograde motion is the orbital motion of a body in a direction opposite that which is normal to spatial bodies within a given system. 'Retrograde' derives from the Latin words retro, backwards, and gradus, step. In the Solar system, mostly everything rotates in the same sense: all major planets orbit the Sun counterclockwise as seen from the pole star (Polaris). Most...

2004-10-19 04:45:44

Cosmogony -- Cosmogony is the study of the origins of celestial objects. It is most commonly used to refer to the study of the origin of the solar system. Currently, the most widely accepted theory is that the solar system was formed roughly 5 billion years ago with the collapse of a nebula of gas and dust, likely caused by shock waves generated by a nearby supernova. The solar system...

Terrestrial Planet
2004-10-19 04:45:42

Terrestrial Planet -- A terrestrial planet is a planet that is mostly composed of silicate rocks and may or may not have a relatively thin atmosphere. The term is derived from the Greek word for Earth, so an alternate definition would be those planets that are more Earth-like than not. Terrestrial planets are very different from gas giants, which may or may not have solid surfaces and...

Solar Nebula
2004-10-19 04:45:42

Solar Nebula -- In astronomy, the solar nebula is the gaseous cloud from which, in the so-called nebular hypothesis of the origin of the solar system, the Sun and planets formed by condensation. In 1755 the German philosopher Immanuel Kant suggested that a nebula in slow rotation, gradually pulled together by its own gravitational force and flattened into a spinning disk, gave birth to the...

Planetary Ring
2004-10-19 04:45:42

Planetary Ring -- A planetary ring is a ring of dust and other small particles orbiting around a planet in a flat disc-shaped region. The most spectacular and famous planetary rings are those around Saturn, but all four of the solar system's gas giant planets (Jupiter, Saturn, Uranus, Neptune) possess ring systems of their own. The origin of planetary rings is not precisely known, but...

2004-10-19 04:45:42

Planet -- A planet is a body of considerable mass that orbits a star and that doesn't produce energy through nuclear fusion. Until recently, only nine were known (all of them in our own Solar system). As of the end of 2002 over 100 are known, with all of the new discoveries being extrasolar planets. Astronomers often call asteroids minor planets, and call the larger planetary bodies...

Gas Giant
2004-10-19 04:45:41

Gas Giant -- A gas giant is a generic astronomical term invented by the science fiction writer James Blish to describe any large planet that is not composed mostly of rock or other solid matter. Gas giants may still have a solid core - in fact, it is expected that such a core is probably required for a gas giant to form - but the majority of its mass is in the form of gas (or gas compressed...

Extrasolar Planet
2004-10-19 04:45:41

Extrasolar Planet -- An extrasolar planet is a planet orbiting around a star other than the Sun. Extrasolar planets were first discovered in the 1990s as a result of improved telescope technology, CCD and computer-based image processing which allowed far more accurate measurements of stellar motions. The first extrasolar planets were reported by the astronomer Aleksander Wolszczan in 1993,...

Word of the Day
  • A fudgelike confection of brown sugar, cream or milk, and chopped nuts.
'Penuche' is a variant of 'panocha,' a coarse grade of sugar made in Mexico. 'Panocha' probably comes from the Spanish 'panoja, panocha,' ear of grain.