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Size of the Solar System

The Solar System is large. How large? Think of the biggest thing you can imagine. It’s bigger than that…And our galaxy contains perhaps a 100 billion stars, all of them separated by vast empty spaces.

Take a second to consider the vast distance between the Earth and the Moon. The radius of the Earth is about 6.4 million meters (6,400 km or 3,970 mi). The distance to the Moon is 384 million meters (384,000 km or 238,000 mi)! That distance is 60 times the radius of the Earth! Take a look at the picture below to get some idea of the vastness of this distance, which on a cosmic scale is really quite small:

Earth_to_Moon_rel.distance (2K)
Earth_to_Moon_Speed_of_light (84K)
The relative sizes and separation of the Earth–Moon system are shown to scale above. The beam of light is depicted travelling between the Earth and the Moon in the same time it actually takes light to scale the real distance between them: 1.255 seconds at its mean orbital distance. The light beam helps provide the sense of scale of the Earth-Moon system relative to the Sun, which is 8.28 light-minutes away (photosphere to Earth surface). This image is from Wikipedia’s Moon page.

Feel insignificant yet? Well, if not then doing this activity might help. You will create a scale model of the solar system by drawing the size of the planets on paper and pacing out the distance between them, taking the radius of the Sun to be 1.0 m. The data you will need are found below:

Solar System Data
Name Orbital
Distance (m)
Radius (m)
Sun 6.95 × 108
Mercury 5.791 × 1010 2.440 × 106
Venus 1.082 × 1011 6.052 × 106
Earth 1.496 × 1011 6.378 × 106
Moon 3.84 × 108 1.738 × 106
Mars 2.2794 × 1011 3.397 × 106
Jupiter 7.7833 × 1011 7.1492 × 107
Saturn 1.4294 × 1012 6.0268 × 107
Uranus 2.87099 × 1012 2.5559 × 107
Neptune 4.5043 × 1012 2.4766 × 107
Pluto 5.91352 × 1012 1.150 × 106
Scaled-Down Solar System
Name Orbital
Distance (m)
Radius (m, cm, or mm)
  1. Take the radius of the Earth to be the same as a standard glass marble (7.5 mm) in your scaled-down Solar System. Construct a proportion you can use to find the scaled down sizes of the sun, planets, and orbits. Ask your teacher for help with this if you need it.
  2. Calculate the scaled-down sizes of the orbits and planets. Fill them in the blank chart above. Your class will split into small groups of 2 or 3 and each group will be assigned a solar system body. Additional data will be provided if there are more groups than objects to model.
  3. Using materials that you gather yourselves, create models of your assigned solar system body. For all but the Sun these models should be three-dimensional and of the correct scaled size. The Sun may be made from paper and may remain a flat circle. The Earth and Moon have already been modeled and reside in your teacher’s classroom.
  4. How much bigger is the radius of the Earth’s orbit (its orbital distance) than the radius of the Earth? Divide the orbital distance by the radius of the Earth. Based on this calculation consider the following: Imagine that you are out in space high above the north pole of the Sun. In fact, you are so far up above the Solar System that you can see the entire orbit of the Earth in one glance. Given the size of the Earth compared to the size of its orbit, do you think you could find the Earth in all that empty space? Why or why not?
  5. The nearest star to the Sun is Alpha Centauri (also written as α Centauri). It is about 4 light-years away (3.78 × 1016 m). One light-year is the distance traveled by light (at 3 × 108 m/s) in one year or 9.46 × 1015 m. Compare the radius of Pluto’s orbit to the distance to α Centauri. How much farther away is α Centauri compared to Pluto’s orbital distance? That is, how many times farther away is the nearest star than the outer edge of the Solar System? What does this tell you about the amount of space between stars in our galaxy?
  6. Use the map provided with this assignment to mark the locations of the planets’ orbits. Set the Earth at the location of your classroom and place the planets on the maps using the maps’ scales.
    Consider: Do the planets all have to be in a straight line on your maps?

To earn a ‘3’ for this assignment, turn in your calculations (showing work for one sample planet), the answers to the questions on this handout, and your model.

To earn a ‘4’ go to a location the correct distance from the classroom for your modeled solar system body and take a picture of your group members holding your model. Turn in a printed-out copy of the photo with your model, questions, and calculations.

There is a page available with some images that can help to prepare students for this activity available. See it here.
Solar System Data in an Excel spreadsheet.
Last updated: Feb 10, 2012 Home