Download The Solar System The Sun is the star at the center of the Solar S

The Solar System
The Sun is the star at the center of the Solar System. It is about five billion years old.
There are nine planets in the Solar System. These planets circle around the Sun. This
is called orbits. A lot of astronomy people think that the Solar System divided into
two parts. The Inner Solar System has Mercury, Venus, Earth and Mars. These are
closest to the sun and they are called the terrestrial planets simply because they have
very solid rocky surfaces.
The Outer Solar System has Jupiter, Saturn, Uranus, and Neptune. They are
sometimes called the gas giants.
These two systems are separated by the asteroid belt.
The Solar System also contains comets, moons, dust, gas and some minor planets.
Mercury
Mercury is the first planet from the Sun. It is named
after Mercury, the messenger of the gods. The planet
speeds around the Sun once every 88 days.
Mercury is a small, rocky world. Mercury is very like
the Moon. Its surface is covered with craters. It has no
atmosphere and no water. The noon temperature at the
equator can be about 450 °C but the nights are
extremely cold, below -180 °C.
Venus
Venus is the second planet from the Sun. It appears as a
brilliant morning or evening “star” – the brightest object in the
night sky apart from the Moon.
In some ways, Venus is Earth’s twin. It is about the same size
and made of the same rocky materials. It also comes closer to
Earth than any other planet.
The planet’s temperature is 465 °C. This means that Venus is
even hotter than Mercury.
Without special protection, a visitor to Venus would die
instantly – crushed by the immense air pressure, suffocated by the atmosphere,
burned to a crisp by the scorching heat, and dissolved by the acid.
The surface of Venus has thousands of volcanoes and impact craters.
Mars
Mars is often called the 'Red Planet' because it appears in
the sky as an orange-red star. Because of color the
ancient Greeks and Romans named it after their god of
war. Mars is the fourth planet from the Sun. It orbits the
Sun at an average distance of 228 million km, so human
visitors would find it very cold. The average temperature
is 63 degrees Celsius below zero – similar to winters in
Antarctica. The nights are also bitterly cold.
Violent storms can whip up clouds of dust. Sometimes these spread rapidly around
the entire planet, hiding the surface from view.
Jupiter
Beyond the asteroid belt is Jupiter, the fifth planet from
the Sun. Everything about Jupiter is large. It is so big
that it could easily swallow all of the other planets (or
more than 1,300 Earths). It also weighs more than
twice as much as all the other planets.
Jupiter is five times as far from the Sun as the Earth, so
its surface temperature is low, around –145 °C.
Jupiter is a giant ball of gas, with no solid surface. It is
mainly made of the very light gases, hydrogen and helium. Telescopes show a cloudy
atmosphere with colorful belts and spots.
Jupiter has a faint ring of dust, over 100,000 km wide. It is also orbited by
63satellites. Four of these, discovered by the Italian scientist Galileo in 1610, are very
big. They are Io, Europa, Ganymede and Calisto.
Saturn the gas giant
Saturn is the sixth planet from the Sun. It was the furthest
of the planets until the telescope was invented.
Saturn is made mainly of the light gases hydrogen and
helium. 764 Earths would fit inside Saturn, but the gas
giant weighs only 95 times as much as our rocky world. In
a telescope, Saturn appears a pale yellow color. It has no
solid surface, so what we are seeing are clouds that appear
as light and dark bands. These clouds are blown along by very strong winds.
Uranus
Uranus is the seventh planet from the Sun. It was discovered by
William Herschel in 1781.
Uranus lies more than 2,800 million km from the Sun. The
temperature of its cloud tops is -214 degrees C. It moves quite
slowly and has a long way to travel, so each orbit lasts 84
years.
Uranus is a giant world, the third largest planet in our Solar
System. 64 Earths would fit inside it. Despite its size, it spins rapidly. A day on
Uranus lasts only 17 hours 14 minutes.
Uranus has 27 moons. None of these are very big. The largest satellites are Oberon
and Titania, both more than 1,500 km in diameter.
Uranus also has at least a dozen dark, dusty rings. At least one ring is created by
meteorites crashing into a small satellite.
Neptune
Neptune was discovered in 1846 by Johann Galle, an astronomer
at the Berlin Observatory.
Neptune turned out to be almost an identical twin of Uranus. It is
57 times bigger than the Earth, but spins quite rapidly – one day
lasts only 16 hours 7 minutes. Its average distance from the Sun
is about 4,500 million km, and one year on Neptune lasts for
almost 165 Earth years.
It has an atmosphere of hydrogen, helium and methane. Its interior is made of ices,
with a possible rocky core. Although the atmosphere is very cold (-220 degrees C),
the blue planet has some very strong winds and violent storms.
Neptune has at least five dark, narrow rings (named after Galle, Le Verrier, Adams
and others who worked to discover the planet).
It has 13 known moons. By far the largest is Triton, an icy world that is bigger than
Pluto. Triton is very cold, so its thin atmosphere has frozen onto the surface.
However, it does have many active ice volcanoes that spurt plumes of gas and dust.
Triton is also unusual because it travels “the wrong way” (east to west) around
Neptune.
Pluto
Pluto was discovered in 1930 by 24 year-old Clyde
Tombaugh, who was using a special machine to compare
photos of the sky. It turned out to be a tiny world, even
smaller than our Moon.
Pluto follows an elliptical (egg-shaped) orbit that varies
between 7,381 million km (49 Sun-Earth distances) and
4,446 million km (30 Sun-Earth distances). Since one orbit lasts 248 years, no one
born on Pluto would ever experience a single birthday!
Very little is known about Pluto. Its surface is extremely cold (-230 degrees C) and
seems to be covered with frozen ices. In recent years it has been fairly close to the
Sun and enjoying a brief summer. Surface ices have vaporized, producing a thin
atmosphere. However, it is now retreating into the cold depths of the Solar System
and this atmosphere will soon freeze again.
Pluto spins “backwards” (east to west) once every 6 days 9 hours. Its largest moon,
Charon, takes the same length of time to orbit Pluto. This means that anyone living
on one side of Pluto would never see Charon. Two smaller moons have recently been
discovered with the Hubble Space Telescope.
For many years, Pluto was accepted as the ninth planet from the Sun (even though it
sometimes comes closer than Neptune). Today, it is regarded as a “ dwarf planet”. It
is also one of the largest members of the Kuiper Belt, a family of icy worlds that
occupy the space beyond Neptune.