The document describes the structures of the solar system, including the sun, planets, dwarf planets, asteroids, and comets. It emphasizes the sun as the largest object, the classification of planets into inner and outer categories, and the definition of dwarf planets. It also covers concepts such as orbits, revolution, and the use of astronomical units for measuring distances in space.

1. The Structures of the Solar
System
Chapter 11.1
p 374-380

2. What is the solar system?
• When looking at the night sky, you will likely see
stars and planets. Sometimes, the first starlike object
you see at night is not a star at all.
• A few of the tiny lights that you can see are part of
our solar system.
• Almost all of the other specks of light are stars.

3. Objects in the Solar System
• Ancient observes looking at the night sky saw
many stars but only five planets – Mercury,
Venus, Mars, Jupiter, and Saturn.
– The invention of the telescope in the 1600s led to
the discovery of additional planets and many
other space objects.

4. The Sun
• The largest object in the solar system is the Sun,
a star.
– Its diameter is about 1.4 million km
– Its made mostly of hydrogen gas
– Its mass makes up about 99 percent of the entire
mass of the solar system
• Inside the Sun, a process called nuclear fusion
produces an enormous amount of energy.
– Some of the energy is emitted as light
• The Sun also applies gravitational forces to
objects in the solar system.
– Gravitational forces cause the planets and other
objects to move around, or orbit, the Sun.

6. Objects That Orbit the Sun
• Planets, dwarf planets, asteroids, and
comets orbit the Sun.
– These don’t emit light.

7. Planets
• An object is a planet only if it orbits the Sun and
has a nearly spherical shape.
• The mass of a planet must be much larger than
the total mass of all other objects whose orbits
are close by.
• Our solar system has eight objects classified as
planets.

8. Inner Planets and Outer Planets
• The four planets closet to the Sun are the
inner planets.
– Mercury, Venus, Earth, and Mars
– These planets are mainly made of solid rocky
materials

9. Inner Planets and Outer Planets
• The four planets farthest from the Sun are called the
outer planets
– Jupiter, Saturn, Uranus, and Neptune
– These planets are mainly made of ice and gases such as
hydrogen and helium.
– Because they are much larger than Earth, we also call them gas
giants.

10. Dwarf Planets
• A dwarf planet is a spherical object that orbits
the Sun.
– It is not a moon of another planet and is in a region of
the solar system where there are many objects
orbiting near it.
– Unlike a planet, a dwarf planet does not have more
mass than objects in nearby orbits
– They are made of rock and ice and are much smaller
than Earth.
– They include Ceres, Eris, Pluto, and MakeMake.

13. Asteroids
• Millions of small, rocky objects called
asteroids orbit the Sun in the asteroid belt
between the orbits of Mars and Jupiter
– They range in size from less than a meter to
several hundred kilometers in length
– Unlike planets and dwarf planets, asteroids
usually aren’t spherical

14. Comets
• A comet is made of gas, dust, and ice and
moves around the Sun in an oval-shaped
orbit.
– Comets come from the outer parts of the solar
system.
– There might be 1 trillion comets orbiting the
Sun.

16. The Astronomical Unit
• On Earth we use meters or kilometer.
• Objects in the solar system, are so far
apart that astronomers use a larger
distance unit.
• An astronomical unit (AU) is the average
distance from Earth to the Sun – about
150 million km.

17. The Motion of the Planets
• Revolution and Rotation
– The time it takes an object to travel once
around the Sun is its period of revolution
• Earth’s period of revolution is one year.
– The time it takes an object to complete one
rotation is its period of rotation
• Earth’s period of rotation is one day

18. The Motion of the Planets
• Planetary Orbits and Speeds
– Unlike a ball swinging on the end of a string, planets do not
move in circles
– Instead, a planet’s orbit is an ellipse – a stretched-out circle
– Inside an ellipse are two special points, each called a focus.
– These focus points, or foci, determine the shape of the ellipse.
– The foci are equal distances from the center of the ellipse.

19. The Motion of the Planets
• Planetary Orbits and Speeds
– A planet’s speed also changes as it orbits the
Sun. The closer the planet is to the Sun, the
faster it moves.
– This also means that planets farther from the
Sun have longer periods of revolution.
– For example, Jupiter is more than 5 times
farther from the Sun than Earth.
• It takes Jupiter 12 times longer than Earth to
revolve around the Sun.