Lunar and Planetary Institute






Solar System - Planet Sizes
EXPLORE! Solar System

Planet Sizes - Part 1

Overview

This activity has three parts that can be used separately or in combination.

What's the Point?

To model the relative scale of the planets and their orbits.

Materials

  • Books or videos about the solar system
  • Solar system fruits and vegetables (Table 1 – Scaled Planet Sizes)
  • Chart paper
  • Paper and colored pencils, markers
  • Paper circles representing each planet (Table 1 – Scaled Planet Sizes). Use newspaper, poster paper, or wrapping paper for Jupiter and Saturn. Attach the smaller planet cutouts to a piece of paper or a paper plate so they do not get lost.

Activity

Though all nine planets are roughly spherical, they come in different sizes. Looking at them in the sky is no real help in comprehending their sizes because, at great distances, even the giant planets seem to be just dots. In fact, a small planet near Earth, such as Mars, can look larger than a giant planet that is far away, such as Neptune. To understand the relative sizes of the planets, children will make models based on planetary diameters.

Table 1. Scaled Planet Sizes

Planet
Planet Diameters
(reduced by factor of one billion)
Food Representative
(be creative!)
Sun
1392 mm
Giant pumpkin
(can use a Halloween orange pumpkin garbage bag)
Mercury
4.9 mm
Coffee bean
Venus
12.1 mm
Large blueberry
Earth
12.7 mm
Cherry
Mars
6.7 mm
Pea
Jupiter
142.8 mm
Large grapefruit or cantaloupe
Saturn
120.6 mm
Very large orange
Uranus
51.3 mm
Kiwi
Neptune
49.1 mm
Apricot or nectarine
Pluto
2.3 mm
Grain of rice

Comparing Planet Sizes

1. If the group is new to astronomy, consider beginning the session by reading a short story about the solar system, such as The Magic School Bus: Lost in the Solar System or My Place in Space. You could also show a short video or part of a video about the solar system.

2. Invite nine children to each hold a piece of fruit in front of the room. Ask all the children what the fruit might represent in a model of our solar system. (the planets) As a group, have the children work to arrange the children holding the fruit in the proper order, starting with the planet/fruit closest to the Sun and working out to the planet/fruit farthest from the Sun.

Ask children questions to promote observation and comparison: Which planet is the largest? Smallest? Most nearly the size of Earth?

3. Using the chart paper, have children direct you in creating a drawing of the solar system.

This step helps focus the children's thinking and refresh them on facts about the solar system. It also enables you to assess their level of understanding. When necessary, prompt them with questions. For example, what object should we start with? (the Sun) What planet comes next? What objects are scattered between the orbits of Mars and Jupiter? (asteroids)

4. After (or as) you draw the solar system picture in Step 1, review the major components of the solar system and planets.

What are the planets in the solar system?
Starting with the planet closest to the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn Uranus, Neptune, and Pluto. One easy way to remember the order of the planets is the phrase My Very Excellent Mother Just Served Us Nacho Pies.

What lies between the planets?
SPACE! There is mostly space between the planets as well as some dust, comet debris, asteroids, the solar wind, and a few spacecraft made by humans.

What is similar about all the planets?
All planets are spherical, spin on their axes, and orbit our Sun in the same direction.

What are some main differences between the planets?
The children will have many ideas! Some of these might be included: Because of their distance from our Sun, the surfaces of the inner planets are warmer than the outer planets. Five planets are solid and four — Saturn, Jupiter, Uranus and Neptune — are made of gas. The gaseous planets have rings. The atmospheres of every planet are different. Mercury and Pluto have essentially no atmosphere and the gaseous planets are nearly all atmosphere. The atmospheres of Venus, Earth, and Mars are different in their densities and compositions.

5. Show the children the planet cutouts in no particular order. Revisit the names and order of the planets. Which planet might be Mercury? Jupiter? (etc.) As they identify each planet, have them line them up in order.

Ask children questions that promote observation and comparison: Which planet is the largest? Smallest? Most nearly the size of Earth? Using the same scale, how large would the circle cutout of the Sun have to be? What surprised you most about this activity?

6. Invite the children to work in groups to color or decorate the planets. If they need a jump start for ideas of what the different planets look like, they can refer to books in the resource section.

Last updated
November 4, 2009

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