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A 3rd Grade Planets Unit: An Introductory Lesson Plan On the Planets and the Solar System

By Terrie Schultz

Are your third graders interested in space and planet identities? Launch a science unit for your third grade class with this introductory lesson plan on planets in our solar system. Your students will love exploring space and learning all about planet facts.

A Lesson Overview

This third grade lesson plan on planets will serve as an introduction to an entire instructional unit on the components of the solar system. It will give students an overview of the solar system, describing how the sun is in the center, and the planets orbit around the sun, and it will show the students the relative sizes of the planets. The teacher can explain that due to Pluto's very small size, even smaller than Earth's moon, and its distant location at the very edge of the solar system, scientists have decided to change its classification, and have redefined it as a dwarf planet.

A Lesson Plan on Planets for 3rd Grade


  • Students will be able to identify all eight planets (nine including the dwarf planet Pluto), and will be able to name the planets.
  • Students will become familiar with and observe the relative sizes of the planets.
  • Students will be able to explain that the planets orbit around the sun, which is located in the center of the solar system.
  • Students will be able to list the order of the planets from the sun.


-Chart paper and markers

-Spherical objects such as balls or fruit corresponding to the relative sizes of the planets. The relative sizes are listed below in millimeters. On the same scale, the sun would be about 1.39 meters (about 4.5 feet) in diameter.

  1. Mercury- 4.9 mm small pea
  2. Venus- 12.1 mm olive or cherry
  3. Earth- 12.7 mm small radish
  4. Mars- 6.8 mm large pea
  5. Jupiter- 142.8 mm small canteloupe
  6. Saturn- 120 mm grapefruit
  7. Uranus- 51.2 mm small tangerine
  8. Neptune- 48.6 mm apricot
  9. Pluto- 2.3 mm sesame seed


Invite students to share facts that they already know about the planets and the solar system while drawing a diagram of the solar system on the chart paper. Lead the students with questions, such as which planet is closest to the sun, which planet comes next, etc. Discuss the relative sizes of the planets, and show students the fruit models.

Explain how the planets orbit around the sun. The closer planets have smaller orbits, and the orbits get larger with increasing distance from the sun. Ask students how long it takes Earth to travel around the sun. (One year, 365 days.) Tell students that since Mercury is the closest planet to the sun, its revolution only takes 88 days, while Neptune takes 165 years, and Pluto takes 248 years to complete one revolution.

Ask students what they think the different planets might be like, and why. For example, Mercury is very hot because it is so close to the sun, while the outer planets are always very cold. The inner four planets, Mercury, Venus, Earth and Mars, are known as the terrestrial planets because they are rocky. Jupiter, Saturn, Uranus and Neptune are known as the gas giants because they are mainly composed of hydrogen and helium gas, and they are very large.

Choose nine students to come to the front of the room, and give one of the objects to each student. Designate an object to be the sun, such as the chart paper. Ask the class which planet is closest to the sun, and have the student holding "Mercury" stand next to the chart. Continue with the rest of the planets in order.

Review Questions:

At the end of this third grade lesson plan on planets, have a verbal review of the lesson objectives as an observational assessment:

  1. What are the names of the eight planets?
  2. Which planet is closest to the sun?
  3. Which planet is largest?
  4. What is the name of the very small, distant dwarf planet?
  5. Which planet is farthest from the sun?
  6. Which are the terrestrial planets?
  7. Which planets are the gas giants?
  8. How long does it take Earth to revolve once in its orbit around the sun?
  9. Which planets are Earth's nearest neighbors?


WIndows to the

Lunar and Planetary