1. THE SOLAR SYSTEM

3. What is the Solar System ?
The Solar System consists of the Sun and those celestial objects bound to it by
gravity. These objects are the eight planets and their 166 known moons, four dwarf
planets and billions of small bodies, including asteroids, icy Kuiper belt
objects, comets, meteoroids, and interplanetary dust.
Broadly, the charted regions of the Solar System are the Sun, four terrestrial inner
planets, the asteroid belt, four gas giant outer planets, the Kuiper belt, the scattered
disc, and ultimately perhaps the hypothetical Oort cloud.
A flow of charged particles from the Sun (the solar wind) permeates the Solar
System. This creates a bubble in the interstellar medium known as the
heliosphere, which terminates at the heliopause, near the scattered disc.
In order of their distances from the Sun, the eight planets are:
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune

4. The Sun (Latin: Sol) is the star at the centre of the Solar System. The Earth
and other matter (including other
planets, asteroids, meteoroids, comets, and dust) orbit the Sun, which by
itself accounts for about 99.8% of the Solar System's mass. Energy from
the Sun, in the form of sunlight and heat, supports almost all life on Earth
via photosynthesis, and drives the Earth's climate and weather.

5. Mercury is the innermost and smallest planet in the solar system, orbiting the Sun
once every 88 days. Mercury is bright when viewed from Earth, ranging from −2.0 to
5.5 in apparent magnitude, but is not easily seen as its greatest angular separation
from the Sun (greatest elongation) is only 28.3°: It can only be seen in morning and
evening twilight. Comparatively little is known about it; the first of two spacecraft to
approach Mercury was Mariner 10 from 1974 to 1975, which mapped only about 45%
of the planet’s surface. The second was the MESSENGER spacecraft, which mapped
another 30% of the planet during its flyby of January 14, 2008. MESSENGER will make
two more passes by Mercury, followed by orbital insertion in 2011, and will survey
and map the entire planet.

6. Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth
days. The planet is named after Venus, the Roman goddess of love. It is the
brightest natural object in the night sky, except for the Moon, reaching an
apparent magnitude of −4.6. Because Venus is an inferior planet from Earth, it
never appears to venture far from the Sun: its elongation reaches a maximum
of 47.8°. Venus reaches its maximum brightness shortly before sunrise or
shortly after sunset, for which reason it is often called the Morning Star or the
Evening Star.

7. Earth is the third planet from the Sun. Earth is the largest of the terrestrial
planets in the Solar System in diameter, mass and density. It is also referred to as
the Earth, Planet Earth, the World, and Terra.
Home to millions of species, including humans, Earth is the only place in the
universe where life is known to exist. Scientific evidence indicates that the planet
formed 4.54 billion years ago, and life appeared on its surface within a billion
years. Since then, Earth's biosphere has significantly altered the atmosphere and
other abiotic conditions on the planet, enabling the proliferation of aerobic
organisms as well as the formation of the ozone layer which, together with
Earth's magnetic field, blocks harmful radiation, permitting life on land.

8. Mars pronounced is the fourth planet from the Sun in the Solar System. The planet is named
after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish
appearance.
Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of
the impact craters of the Moon and the volcanoes, valleys, deserts and polar ice caps of Earth. It
is the site of Olympus Mons, the highest known mountain in the Solar System, and of Valles
Marineris, the largest canyon. Furthermore, in June 2008 three articles published in Nature
presented evidence of an enormous impact crater in Mars' northern hemisphere, 10,600 km
long by 8,500 km wide, or roughly four times larger than the largest impact crater yet
discovered, the South Pole Aitken basin. In addition to its geographical features, Mars’ rotational
period and seasonal cycles are likewise similar to those of Earth.

9. Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is two
and a half times as massive as all of the other planets in our Solar System combined. Jupiter is
classified as a gas giant, along with Saturn, Uranus and Neptune. Together, these four planets
are sometimes referred to as the Jovian planets, where Jovian is the adjectival form of Jupiter.
The planet was known by astronomers of ancient times and was associated with the
mythology and religious beliefs of many cultures. The Romans named the planet after the
Roman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of
−2.8, making it the third brightest object in the night sky after the Moon and Venus.

10. Saturn is the sixth planet from the Sun and the second largest planet in the Solar
System, after Jupiter. Saturn, along with Jupiter, Uranus and Neptune, is classified as a gas
giant. Together, these four planets are sometimes referred to as the Jovian planets, where
Jovian is the adjectival form of Jupiter.
Saturn is named after the Roman god Saturnus, equated to the Greek Kronos and the
Babylonian Ninurta. Saturn's symbol represents the god's sickle.
The planet Saturn is composed of hydrogen, with small proportions of helium and trace
elements. The interior consists of a small core of rock and ice, surrounded by a thick layer
of metallic hydrogen and a gaseous outer layer. The outer atmosphere is generally bland in
appearance, although long-lived features can appear. Wind speeds on Saturn can reach
1,800 km/h, significantly faster than those on Jupiter. Saturn has a planetary magnetic field
intermediate in strength between that of Earth and the more powerful field around Jupiter.

11. Uranus or is the seventh planet from the Sun and the third-largest and fourth-most massive
planet in the solar system. It is named after the ancient Greek deity of the sky (Uranus), the
father of Kronos (Saturn) and grandfather of Zeus (Jupiter). Though it is visible to the naked
eye like the five classical planets, it was never recognized as a planet by ancient observers
due to its dimness and slow orbit. Sir William Herschel announced its discovery on March
13, 1781, expanding the known boundaries of the solar system for the first time in modern
history. This was also the first discovery of a planet made using a telescope.

12. Neptune is the eighth and farthest planet from the Sun in the 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 massive than its near-twin Uranus, which is 15 Earth masses and
less dense. The planet is named after the Roman god of the sea.
Discovered on September 23, 1846, Neptune was the first planet found by mathematical
prediction rather than regular observation. Unexpected changes in the orbit of Uranus led
astronomers to deduce the gravitational perturbation of an unknown planet. Neptune was
found within a degree of the predicted position. The moon Triton was found shortly
thereafter, but none of the planet's other 12 moons were discovered before the 20th
century. Neptune has been visited by only one spacecraft, Voyager 2, which flew by the
planet on August 25, 1989.

13. A star is a massive, luminous ball of plasma. The nearest star to Earth is the Sun, which is the
source of most of the energy on Earth. Other stars are visible in the night sky, when they are
not outshone by the Sun. For most of its life, a star shines because thermonuclear fusion in its
core releases energy that traverses the star's interior and then radiates into outer space.
Almost all elements heavier than hydrogen and helium were created by fusion processes in
stars. Astronomers can determine the mass, age, chemical composition and many other
properties of a star by observing its spectrum, luminosity and motion through space. Other
characteristics of a star are determined by its evolutionary history, including the
diameter, rotation, movement and temperature. A plot of the temperature of many stars
against their luminosities, known as a Hertz sprung-Russell diagram allows the age and
evolutionary state of a star to be determined. The star which is closest to the Earth is the Sun.

14. A meteorite is a natural object originating in outer space that survives an impact with the
Earth's surface. While in space it is called a meteoroid. When it enters the
atmosphere, impact pressure causes the body to heat up and emit light, thus forming a
fireball, also known as a meteor or shooting star. The term bolide refers to either an
extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like
meteor regardless of whether it ultimately impacts the surface.
More generally, a meteorite on the surface of any celestial body is a natural object that has
come from elsewhere in space. Meteorites have been found on the Moon and Mars.

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