Solar System

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					Our Sun and eight planets with their moons make up what astronomers call
the -œSolar System-•. Although our Solar System is not the only one in
the galaxy, scientists have not yet found the one like it. Each planet in
the Solar System is as unique as the system in which it orbits. As a
matter of fact, eight planets have very few attributes in common. They
similarly orbit around the Sun, and they have largely the same chemical
compositions. Beyond those two properties, the planets contrast far more
sharply than they neatly compare. The Sun's gravity and magnetic field,
called the -œheliosphere-•, envelop the major planets and all the dwarf
planets in the Solar System. Although we frequently represent the
planets' orbits as circular, the major planets actually trace cosmic
ellipses as they rotate around the Sun. The planets of the solar system
take their names from Roman gods and goddesses. Of course, -œJupiter-•,
by far the largest of the eight planets, is named for the King of the
Roman gods. Saturn, frigid and ice-bound almost beyond measure and
imagination, paradoxically carries the name of the Roman god of
agriculture. Mars, relatively small and desolate, carries the name of the
Romans' war god. Until 1977 scientists thought only Saturn had -œrings-•
- vast planes of ice and rocks suspended in orbit around them. Further
investigation has shown that Uranus and Neptune also have ring systems.
Naturally, their ring systems are not so pronounced as Saturn's, because
they are proportional to the two much smaller planets. Astronomers refer
to the bodies we generally call -œmoons-• as -œsatellites-•, and our moon
has generally the same characteristics and properties as the other 139
satellites in the Solar System: it orbits the Earth as the Earth orbits
the Sun, held in its elliptical pattern around the third planet by
gravity and magnetism much like the Sun holds the planets. In the last
several years debate has raged over Pluto's status: does it qualify as a
planet, or does it fall into some other category of celestial objects?
In the course of the debate over Pluto the International Astronomical
Society (IAS)    the governing body that sets standards for measurements,
observations, and discoveries    changed the definition of and criteria
for a planet. In order to meet official planet standards, a celestial
body must orbit the Sun, have sufficient gravity to maintain a uniformly
spherical shape, and clear its own orbit. After the IAS established its
current standards, Pluto no longer met the requirements. Astronomers,
after changing their assessments several times, finally classified Pluto
as a -œdwarf planet-•. Pluto travels in a little cluster of celestial
objects very much like it, and astronomers developed an official
classification for the whole group, calling these objects -œplutoids-•.
They have gravity and hold their shape as they orbit the Sun, but they
have not cleared their orbits. Many astronomers have become fascinated
with the plutoids, arguing that insight into their development and
evolution will contribute to proving -œThe Big Bang Theory-•. You can
find more information about Solar System and planets of the solar system
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