Grade 3
The Human Knowledge Project
Unit 11 — Earth and Space
Welcome back!
Have you ever looked up at the night sky and wondered what lies beyond Earth?
Our planet is part of a much larger universe filled with stars, planets, moons, galaxies, and many other amazing objects.
Today we will explore our place in space.
Earth
Earth is our home.
It is the third planet from the Sun.
Earth is special because it has:
- liquid water
- an atmosphere
- a wide variety of plants and animals
- temperatures that allow life to exist
As far as scientists currently know, Earth is the only planet known to support life.
The Sun
The Sun is a star.
It gives Earth:
- light
- heat
- energy
Without the Sun:
- plants could not grow
- animals could not survive
- Earth would become extremely cold
Nearly all life on Earth depends on the Sun.
The Moon
The Moon is Earth's natural satellite.
It travels around Earth about once every month.
The Moon does not make its own light.
Instead, it reflects light from the Sun.
As the Moon orbits Earth, we see different phases such as:
- new moon
- first quarter
- full moon
- last quarter
The Solar System
Our Solar System includes:
- the Sun
- eight planets
- dwarf planets
- moons
- asteroids
- comets
The eight planets, in order from the Sun, are:
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
Each planet has its own unique features.
Stars
The Sun is only one of billions of stars.
Stars vary in:
- size
- color
- brightness
- temperature
Some stars are much larger than the Sun.
Others are much smaller.
The stars we see at night are extremely far away.
Galaxies
A galaxy is a huge collection of stars, planets, gas, and dust held together by gravity.
Earth is part of the Milky Way Galaxy.
The Milky Way contains hundreds of billions of stars.
Scientists believe the universe contains billions of galaxies.
Day and Night
Earth spins on its axis once every 24 hours.
The side facing the Sun experiences:
day
The side facing away from the Sun experiences:
night
Earth's rotation creates the daily cycle of day and night.
Seasons
Earth also travels around the Sun once each year.
Because Earth's axis is slightly tilted, different parts of Earth receive different amounts of sunlight during the year.
This creates the seasons:
- spring
- summer
- autumn (fall)
- winter
The seasons change gradually as Earth continues its journey around the Sun.
Activity
Create a simple model of the Solar System.
Draw:
- the Sun
- the eight planets
Label each planet in the correct order.
Then answer:
Which planet is Earth?
Which planet is the largest?
Practice
Answer these questions.
Why is Earth able to support life?
What does the Sun provide?
Why does the Moon appear to change shape?
Name the eight planets in order.
What causes day and night?
Why do seasons occur?
Review
Today you learned:
- Earth is our home planet
- the Sun is a star that provides energy
- the Moon reflects sunlight
- the Solar System contains eight planets
- galaxies contain enormous numbers of stars
- Earth's rotation creates day and night
- Earth's tilted axis and orbit create the seasons
Looking into space reminds us that Earth is part of a vast and fascinating universe waiting to be explored.
Looking Ahead
Next we begin our Grade 3 Social Studies units.
You will learn how maps, landforms, climates, and natural resources help people understand the world and how geography influences the way communities live and grow.