Pocket Solar System

Students will be able to:

1. describe the relative distances between the orbits of the planets.
2. recognize that objects in the solar system are very far from each other.

• orbit: The path followed by an object in space as it goes around another object; to travel around another object in a single path.
• planet: In the solar system, a planet is a large round object that orbits the Sun and has cleared out most of the other objects in its orbit.
• dwarf planet: A large round object that orbits the Sun but is NOT the dominant object in its orbit.
• solar system: The Sun and all of the planets, comets, etc. that revolve around it.

1. Distribute the register tape and stickers to each student and lead them through the following steps.
   
2. Sun & Pluto (on the edges): Make a mark on each end of the tape, one large and one small, right at the edge. Label the large one Sun and the small one Pluto. Even though Pluto has been reclassified as a dwarf planet it serves as a useful reference point here. We can use it as the first example of such a dwarf planet ever found, just as we'll use Ceres to represent the asteroid belt later on.
   
3. Uranus (1/2): Fold the tape in half, crease it, unfold and lay flat. Place a large sticker at the halfway point. You can ask for guesses as to which of the planets might be at this halfway point. Label the sticker Uranus.
   
4. Saturn (1/4) and Neptune (3/4): Fold the tape back in half, then in half again. If there are mixed ages, give those with some knowledge of fractions the opportunity to show off by asking "What is half of a half?" Unfold and lay flat. Place large stickers at the quarter mark and 3/4 marks and label as Saturn (closer to the Sun) and Neptune (closer to Pluto).
   
5. Jupiter (1/8): Fold back into quarters, then in half one more time. This will give you eighths. Unfold and lay flat again. Place a large sticker for Jupiter at the 1/8 mark (between the Sun and Saturn), and label.
   
6. Asteroid Belt (1/16): No need to fold the whole thing up again. If you take a look, you've got the 4 gas giants and Pluto all on there in the outer solar system. For the remaining terrestrial planets, you'll only need 1/2 of the first 1/8th! That's the inner 1/16th of your meter. Fold the Sun out to meet Jupiter to mark the 1/16th spot. A planet does not go here, but you should label this Ceres to represent the Asteroid Belt.
   
7. Earth (inside 1/32), Mars (outside 1/32) : At this point, things start getting a little crowded and folding is tough to get precise distances, so fold the remaining 1/16th in half and crease at the 1/32nd spot. Place a small sticker for the Earth just inside this fold (between the Sun and Ceres) and a small sticker for Mars just outside the fold (closer to Ceres and the Asteroid Belt) and label them.
   
8. Mercury & Venus (between Earth & Sun): Place small stickers for Mercury and then Venus, between the Earth and Sun, pretty much dividing the space into thirds and label them as Mercury closest to the Sun and Venus closest to the Earth.

Models and illustrations of the Solar System often misrepresent the true scales and distances involved. The difficulty lies in the vast difference between the relative sizes of these objects and the distance between them. For example, an accurate model using a 1" sphere to represent the Sun results in a distance to Pluto of over 350 feet (more than a football field away), and most of the planets would appear no larger than tiny specks.

It is usually beneficial to address these two dimensions separately, using one model to compare planet sizes and another to illustrate relative distances from the Sun. By combining this activity with the activity "Worlds in Comparison", teachers can address the misconceptions prevalent in our depictions of the Solar System.

Distances in the solar system are difficult even for astronomers to picture, as they are far beyond our normal experience on Earth. For example, the distance from Earth to the Sun is about 93 million miles — to travel an equivalent distance on Earth, you would need to circle the globe 3,700 times! For the inner planets, the distances to the Sun are similar, ranging from 1/2 to 1 1/2 times that of Earth, but the outer planets are much, much farther away — a fact that is often glossed over in textbook illustrations. This activity creates a simple model that more accurately illustrates the distances to planetary orbits relative to each other.

One way to think about these concepts is to compare the relative distances of the other planets from the Sun to that of the Earth. Astronomers use the mean distance of the Earth to the Sun as a standard unit, called an astronomical unit, or AU. Using this standard, the approximate average distances for each of the planets (and some dwarf planets) are:

• Mercury .5 AU
• Venus .7 AU
• Earth 1 AU
• Mars 1.5 AU
• Ceres 2.5 AU
• Jupiter 5 AU
• Saturn 9.5 AU
• Uranus 20 AU
• Neptune 30 AU
• Pluto 40 AU

This lesson was originally developed by Amie Gallagher, Raritan Valley Community College, and adapted by Suzanne Gurton and Anna Hurst, Astronomical Society of the Pacific, 2008.

This lesson was originally developed by Amie Gallagher, Raritan Valley Community College, and adapted by Suzanne Gurton and Anna Hurst, Astronomical Society of the Pacific, 2008.

Image: "Solar System" by NASA-JPL, originally sourced from https://commons.wikimedia.org/wiki/File:Solar_sys.jpg