Solar System Scale

Astronomy:	Planet Scale, Solar System Scale
Grade Range:	Elementary School, Middle School, High School
Format:	Hands-on, Stage

Materials

• Solar System Box
• Two Sun Boards
• Cord with Paper Clip Markers

Safety Precautions

Please read the General Safety section of the Demonstration Safety page before performing this demonstration.

Demonstration

Presentation (Stage)

1. Set up one half of the sun and connect the string to it. Explain to the audience that they are about to see a scaled-down version of our solar system.
2. Ask the audience to name the planets in order as you hang them. Be sure to give some quick facts on each planet (listed in Why This Works) Pause when you get to Mars, and explain that these four planets are the rocky planets. Have your co-presenter pull out the other half of the sun and set it up about six feet away from the first half, and emphasize the size difference.
3. Continue to have the audience name the planets as you hang them until you have all the planets on the string. Have your co-presenter hold the sun in place, or it might fall over!
4. Once you have all the planets on the string, Ask the audience if they can guess how far away the nearest neighboring star, Proxima Centauri, would be on this scale. Allow a few guesses until you reveal that it would be about 50 miles away!

Presentation (Hands-on)

1. Set up the string of planets, and connect the string to the sun. Set the sun and the string along a wall, and have the end of the string suspended on a hook or pole.
2. Allow students to come up to the string, and walk them down the length of the string so to see how big and small the planets are compared to each other. Provide some fun facts on the planets as you do so.

Why This Works

The purpose of this demonstration is to give a very visual representation of the relative sizes and distances to the different planets. Almost all of the students you present this to will have heard of the planets, but it might be hard for them to visualize the size of the other planets in our solar system, and the size of the earth in comparison. The table below lists the information you need when naming all the planets.

Planet	Length of Day/ Length of Year	Size	Fun Facts
Mercury	1 day = 172 Earth Days 1 Year = 88 Earth Days	Size = ~0.4 Earths	Mercury has one full day every two years. Temperatures on Mercury can vary from -260 F to 800 F! Mercury has frozen water at its north and south poles!
Venus	1 day = 243 Earth Days 1 Year = 224 Earth Days	Size = 0.95 Earths	Venus is the hottest planet in our solar system, averaging 863 F each day! Venus has a toxic atmosphere made mostly of CO2, with clouds of sulfuric acid. The atmosphere is so dense on Venus that trying to stand on the surface would be like trying to stand while 1 k deep in an ocean!
Earth	Unit for 1 Day Unit for 1 Year	Unit for Size	Earth is the only inhabited planet in our solar system, and our home planet. Earth currently supports approximately 7.4 billion people, as well as over 1 million other kinds of animals! Earth also supports approximately 3 trillion trees, as well as over 500,000 other kinds of plants!
Mars	1 Day = 1.02 Earth Days 1 Year = 1.9 Earth Years	Size = 0.53 Earths	There are seven active spacecraft visiting Mars, with five in orbit and two on the surface. Mars has frozen water, and some of the spacecrafts are searching for evidence of previous life on Mars. Mars has seasons, but they are about twice as long as the ones we have on Earth.
Jupiter	1 Day = 9 Hours 55 min 1 Year = 11.8 Earth Years	Size = 1,321 Earths	Jupiter is the most massive planet in our solar system, having 2.5 times more mass than all the other planets combined! Jupiter has 67 known satellites, the largest being comparable in size to Mercury. Jupiter's Great Red Spot is a storm that has been happening for over 350 years!
Saturn	1 Day = 10 h 33 min 1 Year = 29.45 Earth Years	Size = 763 Earths	Saturn's largest moon, Titan, is bigger than Mercury and has an atmosphere. It is the biggest moon in the solar system. Saturn has a hexagonal cloud pattern on it's north pole, which is thought to be a standing wave pattern on the planet. The rings of Saturn are twice as wide as the planet, and Saturn's many moons help to shepherd the rings into place!
Uranus	1 Day = 17 h 14 min 1 Year = 84 Earth Years	Size = 63 Earths	Uranus is the coldest planet in the solar system, with recorded temperatures as low as -371 F! Uranus spins sideways like a tire, unlike most planets in the solar system. Unlike the other gas giants, there is little cloud activity on Uranus, and it rarely shows any changes in it's atmosphere.
Neptune	1 Day = 16 h 6 min 1 Year = 164 Earth Years	Size = 58 Earths	Neptune is 17 times more massive than earth, but 19 times less massive than Jupiter. There are three large storms on Neptune: The Great Dark Spot, The Small Dark Spot, and Scooter, a band of fast-moving clouds. Neptune is so far from the sun, it takes over four hours for light from the sun to reach it!

This demonstration uses two separate size scales, simply because a single size scale would either make the orbits too big or the planets too small.

• For the distances of the planets from the sun, we are using a scale where the earth is about one foot from the sun. This scale helps students to see not only how close we really are to our sun in an astronomical sense, but also shows how far away some of the other planets are. If we were to use the correct size scale with this distance scale, the earth with be about the size of a speck of dust, and the sun around the size of a basketball!
• For the size of planets, we have a scale which puts the earth at about three quarters of an inch in diameter. This is pretty small, and for one main reason: the sun. Our sun isn't a big star, but stars are extremely large astronomical bodies in the universe. With an earth this small, our sun is about seven feet in diameter! If we used the correct distance scale with this size scale, then our earth would be about 770 feet away from the sun, and Proxima Centauri would be 39,000 miles away!

Additional Information

• This demonstration pairs well with the Planetary Compositions demonstration.
• This demonstration is a part of the Astronomy Show.