The Solar System
For I dipped into the Future, far as human eye could see; saw the vision of the world, and all the wonder that would be. -Alfred Lord Tennyson, 1842
(TFS) - The solar system consists of an average star
called the sun around which turns eight official planets ;Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus, Neptune, a dwarf planet called Pluto and
millions of small planets called astroids.
Other celestial bodies are also present, such as formed comets of rocks and
ice ; Meteorites, which are rock debris and satellites rotating around
large planets, such as the Moon, which is the Earth’s satellilte.
The Solar system was formed 4.6 billions of years ago.
The whole solar system, together with the local stars
visible on a clear night, orbits the center of our home galaxy, a spiral disk
of 200 billion stars we call the Milky Way.
The Milky Way has two small galaxies orbiting it nearby, which are visible from
the southern hemisphere. They are called the Large Magellanic Cloud and
the Small Magellanic Cloud. The nearest large galaxy is the
Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as
massive and is 2 million light years away. Our galaxy, one of billions of
galaxies known, is traveling through intergalactic space.
The solar system consists of the Sun; the eight
official planets, at least three "dwarf planets", more than 130
satellites of the planets, a large number of small bodies (the comets and
asteroids), and the interplanetary medium. (There are probably also many more
planetary satellites that have not yet been discovered.)
Orbits
The inner solar system contains the Sun, Mercury,
Venus, Earth and Mars:
The planets of the outer solar system are Jupiter,
Saturn, Uranus, and Neptune (Pluto is now classified as a dwarf planet)
The orbits of the planets are all more or less in the same plane (called the
ecliptic and defined by the plane of the Earth's orbit). The ecliptic is
inclined only 7 degrees from the plane of the Sun's equator.
Composition
of the Solar system planets
The Solar system planets are divided into two categories ;
*Terrestrial Planets: Mercury,
Venus, Earth And Mars, Terrestrial planets which are made of rock material have
a solid surface. Their size is not very important and they do not own many
satellites (Mars has two, Earth, only one)
*Giant Planets:
Jupiter, Saturn, Uranus and Neptune are essentially
made up of gas, their surface is not hard. These planets are voluminous ;
Jupiter, for example, is eleven times larger than the earth. These planets are
surrounded by rings and have many satellites.
Pluton is also a gas ball.
The
Future of the Solar system
Scientists believe that the solar system
will disappear one day, for the sun is merely a star which is gradually
burning. The sun will grow bigger and bigger to the point where i twill raise
the earth’s temperature up to 2000°C.
However, the day it will stop burning, the solar system will fall into an
eternal state of darkness and freezing coldness.
Classifications
The satellites of the planets; the large number of
asteroids (small rocky bodies) orbiting the Sun, mostly between Mars and
Jupiter but also elsewhere; the comets (small icy bodies) which come and go
from the inner parts of the solar system in highly elongated orbits and at
random orientations to the ecliptic; and the many small icy bodies beyond
Neptune in the Kuiper Belt.
With a few exceptions, the planetary satellites orbit in the same sense as the
planets and approximately in the plane of the ecliptic but this is not
generally true for comets and asteroids.
The classification of these objects is a matter of minor controversy. Traditionally,
the solar system has been divided into planets (the big bodies orbiting the
Sun), their satellites (a.k.a. moons, variously sized objects orbiting the
planets), asteroids (small dense objects orbiting the Sun) and comets (small
icy objects with highly eccentric orbits). Unfortunately, the solar system has
been found to be more complicated than this would suggest:
There are several moons larger than Pluto and two
larger than Mercury;
there are many small moons that are probably started
out as asteroids and were only later captured by a planet;
comets sometimes
fizzle out and become indistinguishable from asteroids;
The eight bodies officially categorized as planets are
often further classified in several ways:
By composition
Terrestrial or Rocky planets: Mercury, Venus, Earth, and Mars:
The terrestrial planets are composed primarily
of rock and metal and have relatively high densities, slow rotation, solid
surfaces, no rings and few satellites.
Jovian or Gas planets: Jupiter, Saturn, Uranus, and Neptune:
The gas planets are composed primarily of hydrogen and helium and
generally have low densities, rapid rotation, deep atmospheres, rings and lots
of satellites.
By size
Small planets: Mercury, Venus, Earth, Mars.
The small planets have diameters less than 13000 km.
Giant planets: Jupiter, Saturn, Uranus and Neptune.
The giant planets have diameters greater than 48000 km.
The giant planets are sometimes also referred to as
gas giants.
By position relative to the Sun
inner planets: Mercury, Venus, Earth and Mars.
outer
planets: Jupiter, Saturn, Uranus, Neptune.
The asteroid belt between Mars and Jupiter forms the
boundary between the inner solar system and the outer solar system.
By position relative to Earth
inferior planets: Mercury and Venus.
closer to the Sun than Earth.
The inferior planets show phases like the Moon's when
viewed from Earth..
superior planets: Mars thru Neptune.
farther from the Sun than Earth.
The superior planets always appear full or nearly so.
By history
Classical planets: Mercury, Venus, Mars, Jupiter, and Saturn.
known since prehistorical times
visible to the unaided eye
Modern planets: Uranus, Neptune.
discovered in modern times
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