How big is our solar system? How about our sun – it looks pretty small when you gaze up at it!
The short answer is, so large that we can hardly imagine it!
Here are 5 demonstrations you can do at home to teach concepts about the solar system, and help your children gain a clear mental vision of the incredible distances in our solar system, and the differences between the planets.
Here’s a one pager that includes all the tables shown below, so you don’t need to print out the entire document to have them handy: SolarSystemFun
1. How big is the sun?
This may sound like an easy question – but you might even be surprised at the result. It’s very difficult to imagine how large our sun is, since it is so far away that is seems quite small.
To do this demonstration, you’ll need a tennis ball, a 12-1/4 long foot long piece of rope or paracord, and a piece of sidewalk chalk.
First, have everyone imagine the earth is the size of a tennis ball. Then, how big would the sun be? Have everyone guess.
Then, demonstrate… if the earth is the size of a tennis ball (they are about 2.7 inches in diameter), the sun would have a diameter of 24-1/2 feet! Have one person stand holding the end of the rope in the center of a large space (at least 25 feet across). A second person should hold the other end of the rope, and walk around the first person in a circle, keeping the rope stretched fully out. As they walk they draw a circle on the ground with the sidewalk chalk. When you are done, you will have a chalk circle 24-1/2 feet in diameter drawn on the ground. That is the size of the sun in comparison to earth!
In this model our moon would have a diameter of about ¾ of an inch – so about the size of a bouncy ball!
2. How large are the gas giants vs. the rocky planets?
Now that you have models of both the sun and Earth, how about guessing the relative size of Jupiter, the largest of the planets in our solar system?
The answer is, approximately 2-1/2 feet in diameter. You can draw another circle using a 1-1/4 foot piece of rope, or demonstrate it with a playground ball if you have one of the appropriate size.
Here are the relative sizes of the planets assuming a 2.7 inch (tennis ball) Earth, so you can model as many as you like!
Planet Feet Inches
Mercury 1.08 inches
Venus 2.52 inches
Moon 0.72 inches
Mars 1.44 inches
Jupiter 2.52 feet
Saturn 2.12 feet
Uranus 10.8 inches
Neptune 10.44 inches
Pluto .48 inches
3. How far away is the sun?
This next demonstration requires a bit of planning ahead. Ideally you would measure out a distance on a straight road with your car, and find a landmark ½ mile from your starting point that can be easily seen.
If the earth was the size of a tennis ball – the sun would be located ½ mile away!
4. How much would you weigh on another planet?
Your weight on another planet depends on its gravity – which in turn depends on both the size of the planet and its mass. Sometimes the answer is surprising!
To do this demonstration, you need a bathroom scale, a calculator, and the table below. It can also be helpful to have a picture showing the relative sizes of the different planets if your kids do not yet understand how much larger the gas giants are than the Earth.
First, weigh your child. Then, ask them to predict their weight on a different planet. (Mars vs. Jupiter will give you the most interesting results!) Once they guess, multiply their weight by the gravitational factors in the table below to calculate their weight on that planet. As an example, if your child weighs 50 pounds on Earth, they will weigh 50 * .92 = 46 pounds on Saturn!
5. Do bigger planets have higher gravity?
After doing the activity above, you can discuss whether larger planets have higher gravity. There is often a guess that Saturn and Jupiter will have similar gravity, due to their (somewhat) similar size. Earth and Mars are also similar in size. However, gravity depends on the mass of the planet as well as its size, which can lead to some surprising differences!
To demonstrate, you need a golf ball and a ping pong ball. They are of similar size, however the density of the golf ball is around 1.13 g/cm3, while the density of the ping pong ball is .08 g/cm3.
This means that the relative density of the ping pong ball to the golf ball would be 7%. This is actually not too far from the relative density of Saturn vs. the Earth of 12%. In spite of its size, Saturn has such low density that it could float in water (assuming of course you can find a large enough lake to float it in!).
Here are the relative densities of the planets vs. Earth – do you see any surprises?
A great online resource to help kids understand the vast distances in our universe is the video http://htwins.net/scale/. This is an amazing and free resource.
Reference: The majority of the calculations in this activity were based on the NASA Planetary Fact Sheet at http://nssdc.gsfc.nasa.gov/planetary/factsheet/. Information on the size and density of the sun were not included on that page and were located separately on the NASA web site.