Why is Neptune blue? Is Saturn the only planet with rings? How many Earths could you fit inside Jupiter? Here is an easy, flexible activity you can do to introduce size scales and cool planet facts for the planets in our solar system ... and have a snack at the end!
I often get asked for ideas for easy, astronomy-related activities that can be done with kids, and one of my favorites is the edible solar system. It’s easy to set up—you just need one trip to the grocery store beforehand so it can be done on relatively short notice. It works for most age groups since you can vary the level of the material you present. It can also be done with any number of kids, whether you are just at home with your family or entertaining a classroom full of children. I once did it with only 24 hours notice with 600 children (!) at a primary school outside of Cape Town, South Africa, so almost anything is possible with this activity.
The goal of the activity is to introduce kids to the size scales of planets in our solar system as well as share some cool science facts about each planet. You can do this in a fairly straightforward way by bringing in different foods (usually fruits) that show the relative size scale of the planets. The Sun is too big so I usually use a comparison in the room. For example, you can set up the activity with: “If we could shrink down the Sun so that it were as big as that wall, let’s see how big each of the planets would be.” One fun way to keep your audience involved is to pull your edible planets out of a bag one by one (possibly in order of distance from the Sun) and ask everyone to guess which planet that food represents.
As you pull out each “planet,” you can highlight cool science facts about them. This activity is extremely flexible since you can vary the level of the information you present based on your crowd. I suggest not pitching too low however: kids start learning/reading/hearing about the planets pretty early on, so I’m often amazed by how much they know.
Preparing the Activity
If you prefer to use nonedible items to represent your planets, balls obviously work well, from the large bouncy balls used for balance in some exercise classes to basketballs to marbles. If you choose to go the edible route, there are many suggestions online of the varieties of foods you can use with to-scale sizes already calculated. I am a big fan of not reproducing hard work that someone has already done, although it’s always good to check a few of the relative sizes to make sure they were calculated correctly.
My planetary edibles of choice are usually fruits, so below I give suggestions for what types of fruit to use, as well as a few interesting facts, for each planet in our solar system. The relative sizes that I suggest all assume that the Sun is roughly 17.5 feet tall, but you can scale up or down depending on the items you would like to use – just be sure to scale everything by the same amount.