Solar System - Planet Distances
EXPLORE! Solar System
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# Planet Distances - Part 2

## 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

• Softball, marbles, peppercorns, and sand to represent the planets
• 3 x 5 index cards or paper plates or bright-colored card stock with each planet representation attached if possible (Table 2 — Scaled Distances from Our Sun)
• Nine 3-foot dowels to attach to the planet cards
• Tape
• Copies of the handout:

• Hopping Across the Solar System for children ages 5–8
Pacing Our Solar Systemfor children ages 9–13
• A large outdoor area

## Activity

Part 2 can be done as an indoor or an outdoor activity. To decide if this works as an outdoor activity, determine how many planets your space accommodates before you start. You do not have to use all the planets, but Mercury to Jupiter should be included to illustrate the scale of our solar system.

You may be able to modify the outdoor version to fit inside by halving the outdoor scale (of planets and distances) or by using only the inner planets. The activity works best if Mercury to Jupiter are included to illustrate the scale of our solar system.

The Exploratorium Web site provides a conversion tool that will let you determine the distances between, and sizes of, planets for any given scale in both English and metric units. For example, if you want to use a model in which the Sun is one inch in diameter, the distances to planets and planet sizes relative to a one-inch Sun are calculated (Pluto would be 0.001 inches in diameter and 354 feet away).

If you are working with children ages 5–8, consider having steps 8 and 9 completed before the children begin the activity so that the planets on the dowels are in place. Use the Hopping Across the Solar System sheet.

If you are working with children ages 9–13, use Pacing Our Solar System sheet.

Table 2. Scaled Distances from Our Sun

 Planet Planet Sizes (reduced by a factor of 10 billion) Average Distance from the Sun (kilometers) Orbit Size (reduced by factor of 10 billion) Sun 13.9 cm (softball) N/A N/A Mercury 0.05 cm (pencil dot on 3 × 5 card) 57,909,000 5.8 m Venus 0.12 cm (sand grain on 3 × 5 card) 108,200,000 10.8 m Earth 0.13 cm (sand grain on 3 × 5 card) 149,600,000 15.0 m Mars 0.07 cm (pencil dot on 3 × 5 card) 227,940,000 22.8 m Jupiter 1.43 cm (marble) 778,400,000 77.8 m Saturn 1.2 cm (marble) 1,423,600,000 142.4 m Uranus 0.51 cm (peppercorn on 3 × 5 card) 2,867,000,000 286.7m Neptune 0.49 cm (peppercorn on 3 × 5 card) 4,488,400,000 448.9 m Pluto 0.02 cm (pencil dot on 3 × 5 card) 5,909,600,000 591.0 m

7. Ask the children how much space would be needed to position the planets properly at the scale used in Part 1. How far would Earth be from the Sun? Pluto?

Estimating is a way to engage the children. Reassure them that this estimate is just guessing and that you are not expecting anyone to know the answer. You may need to remind the children that scale involves showing relationships of size and distance accurately.

At the scale used in Part 1, Earth would be about a mile from the Sun and Pluto would be about 36 miles away. Ask the children what they might find about a mile or 36 miles from where they are now.

8. Explain that the planets in Part 1 are 100 million times smaller than the actual planets — it would take 100 million of the Part 1 "Earths" placed side-by-side, for example, to equal the actual diameter of Earth.

To properly space the planets so they fit in a reasonable-sized space, such as a yard or football field, you must further reduce their size by a factor of 100, which is 10 billion times smaller than the actual planets! Show them the cards or plates with dowels with the dots and peppercorns attached, as well as the other objects at this scale. Have children identify the planet each object represents and label the card with the planet's name.

9. Go outside and position the "Sun." Provide the Pacing Our Solar System handout to each child. Assign a planet marker to a child (or children, depending on group size) and have the group pace the distance to Mercury, with one long stride being roughly equal to a meter (and a meter is about a yard, or three feet). Have the Mercury child/children remain at the marker. Continue in this fashion until all the markers are placed.

In marking the distances, make sure you remember to start counting with the number at which you left off (i.e., count to five yards, then start at five until you reach nine yards, etc.). If you are limited by distance, have children place as many planets as possible. Discuss how far they would have walk to be able to place the remaining markers.

10. Regroup. Have the children start at the Sun and walk through the markers. Have them count the number of "average" steps or hops between each planet. Note the size of each marker representing a planet. Invite them to share what they know about the planet and have them refer to their handout.

How far from the Sun is the planet? If we were traveling to the planet, how long would it take to get there? From each planet, look back at the "Sun" and imagine how it would appear.

Point out that as one travels to the outer solar system, the great distance from the Sun means that it is quite cold. Temperatures are a scalding 380°C (715°F) on Mercury, –70°C (–94°F) on Mars, –143°C (–225°F) at Jupiter, and a frigid –235°C (–390°F) at Neptune and Pluto.

11. When you get to Pluto, ask the children: How far away at this scale do you think it would be to Alpha Centauri, the nearest star?

Most are likely to say no more than a few miles. Actually, at this scale, Alpha Centauri would be about 11 centimeters across and 3200 kilometers (2000 miles) away, roughly the distance from New Orleans to San Francisco. The brightest star in our sky is Sirius. At this scale it would be about 23 centimeters across and 6500 kilometers away (4000 miles), roughly the distance from New Orleans to Hawaii. For such small objects to be visible at such large distances, stars (including our Sun) clearly must radiate a great deal of energy.

Last updated
October 9, 2009