I.                    Chapter 18  Inner and Outer Planets

1. Astronomy is the study of the Sun, Moon, stars, and other objects in space.

II.                 The Universe

A.     The Universe is all of space and everything in it.

B.     It is made up of many galaxies.

1.  A galaxy is a system of dust, gas, and many millions of stars held together by gravity.

2. We live in the Milky Way galaxy.

III.               Our Solar System

A.     The solar system includes the sun, the planets, their moons, and other objects.

B.     Planets

1.   They are cooler and smaller than stars.

2.   They shine by reflected light from a star.

C.     Our solar system has 9 planets that revolve around the Sun.

D.     The asteroid belt is between Mars and Jupiter.

1.  Asteroids are rocky objects that orbit the Sun.

E.      Gravity keeps the planets moving in circular paths instead of straight paths.

IV.              The Inner Planets

A.     Mercury

1.   Closest to the Sun.

2.   Mercury is very hot during the daytime.

3.   It is very cold at night because it has no atmosphere to hold in the heat.

4.  It has many craters made by meteorites crashed into its surface.

a)    Meteors are pieces of rock and dust that orbit in space.

b)  When they strike the surface of a planet they are called meteorites.

B.     Venus

1.  Second planet from the Sun

2.  Surrounded by a thick atmosphere of hot, poisonous clouds

3.   The atmosphere would poison any living thing on the planet.

4.  Too hot for life

5.  It is the brightest object in the night sky because its atmosphere reflects the Sun’s light.

C.     Earth

1.  Third planet from the Sun

2.  Atmosphere supports life

3.  Only planet with liquid water

4.  Largest rocky planet in the solar system

5.  Only planet known to support life

6.  The Earth has one Moon

a)  It is a satellite of Earth.

b)  A satellite is an object that orbits another object in space.

D.     Mars

1.    Fourth planet from the Sun.

2.   Huge dust storms cover the entire planet.

3.   The rocks and soil contain iron which makes them red.

4.   Two moons

5.  Nicknamed “The Red Planet”

V.                 Outer Planets

A.     Four Gas Giants

1.    Jupiter

a)   Fifth planet from the Sun

b)  Largest planet

c)  Has more moons than any other planet

(1)  63 moons

d)  The Great Red Spot is a storm that has been raging for hundreds of years.

2. Saturn

a)   Sixth planet from the Sun

b)   Brilliant ring system orbits the planet.

c)    The rings are made of water, ice, dust, and chunks of ice.

3. Uranus

a)   Seventh planet from the Sun

b)  Only planet that rotates on its side

4.  Neptune

a)   Eighth planet from the Sun

b)   Smallest of the 4 gas giants

B.     Pluto is an outer planet, but not made of gases.

1. Pluto has a solid, icy surface.

2.  Pluto has an unusual orbit that is tilted and that at times takes it closer to the Sun than Neptune.

3. Charon is Pluto’s only moon.