Grade 8 Integrated Science Chapter 11 Lesson 1; this is a short introduction into the structures of our solar system including basic units of measurement and introduction to our planets.

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.