Download The solar system

Chapter 15: The Solar System
• The Solar System
• The Planets
The solar system
• Ancient observers
noticed that five bright
objects seemed to
wander among the stars
at night.
• They called these
objects planets, from
the Greek word meaning
“wandering star,” and
named them Mercury,
Venus, Mars, Jupiter,
and Saturn.
The solar system
• Today we know that planets are not stars.
• Stars give off their own light.
The Sun is the largest object
in our solar system.
Gravitational force
•
Newton’s law of
universal gravitation
explains how the
strength of gravity
depends on the mass
of the objects and the
distance between
them.
Gravitational force
• Gravitational force is the force of attraction
between all objects.
• All objects that have mass attract each other.
Orbits
•
•
An orbit is a regular, repeating
path that an object in space
follows around another object.
An object in orbit is called a
satellite.
Orbits
•
In 1600, German
mathematician
Johannes Kepler
determined that the
orbits of the planets
were not perfect
circles but slightly
elliptical.
Orbits
•
•
Isaac Newton explained that
an orbit results from the
balance between inertia (the
forward motion of an object
in space), and gravitational
force.
Without the pull of gravity, a
planet would travel off into
space in a straight line.
The solar system
• The solar system includes the Sun, eight
major planets, and their moons.
• A large number of smaller objects are also
part of the solar system, including dwarf
planets, asteroids, comets, and meteors.
7.2 Overview of the planets
• The planets are commonly classified in
two groups.
• The terrestrial planets include Mercury,
Venus, Earth, and Mars.
• The gas planets include Jupiter, Saturn,
Uranus, and Neptune.
• Pluto is not a terrestrial or gas planet, but
now placed in a class of its own.
Comparing size and distance
• The Sun is by far
the largest object
in the solar
system.
• One astronomical
unit (AU) is equal
to 150 million km,
or the distance
from Earth to the
Sun.
Asteroids and comets
• An asteroid is an
object that orbits the
sun but is too small to
be considered a
planet.
• The largest asteroid,
named Ceres, is 933
kilometers (580 miles)
across.
Asteroids and comets
• We believe comets
are made mostly of
ice and dust.
• A comet’s tail can
stretch for millions of
kilometers into space
and faces away from
the sun as the comet
continues its orbit.
Meteors and meteorites
• Occasionally, chunks of
rock or dust break off
from a comet or asteroid
and form a meteor.
• As Earth orbits the sun,
it passes through this
debris, creating a
meteor shower as the
small bits of dust burn
up in the atmosphere.
Meteors and meteorites
• If a meteor is large
enough to survive the
passage through
Earth’s atmosphere
and strike the ground, it
becomes a meteorite.
Earth
• Earth is a small, rocky
planet with an
atmosphere that is made
of mostly nitrogen (78
percent N2) and oxygen
(21 percent O2).