How Big Is the Solar System?

The Solar System is a really big place. In fact, it’s so big that it’s kind of hard to get a handle on.

The biggest problem is that the distances and sizes we use when talking about the Solar System are measured using numbers that are unlike any that you use in daily life—because they’re huge!

But, lucky for us, there is a way to deal with these big numbers and create a mental image of the Solar System that will help you understand exactly how we and everything else fit into it. And that way is to build ourselves a scale model.

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Our Model of the Solar System

To build our model of the Solar System, we need to start by establishing our playing field. And I mean this quite literally, because that’s where we’re going to build our model—on a regulation-sized American football field.

If you’d prefer, you can follow along mentally by imagining walking the length of a football field with us. But I think you’ll get an even better feeling for the true size of the Solar System if you actually make a visit to your local high school football field and march out the distances for yourself (especially if you bring the kids along!) Once we arrive at the football field, we only need a few US coins and a couple of dollar bills to make our model.

To get started, walk to the nearest end zone. Once you’re there, take out a quarter and place it on the goal line. That quarter is your model of the Sun (our friendly local star.) Of course, the Sun is much, much bigger than a quarter—it’s diameter is about 57.3 billion times the diameter of that quarter! But that’s kind of large to fit on a football field, so we’re going with this 57.3 billion-to-1 scale model instead.

Terrestrial and Giant Planets

The Solar System can be divided into a number of “neighborhoods” that each contain several similar planets. This arrangement wasn’t an accident or a coincidence–it’s all a result of how the Solar System formed a little more than 4.5 billion years ago.

The main things that we need to know for today’s model building is that there are 4 planets that are located fairly close to the Sun. These planets—Mercury, Venus, Earth (home!), and Mars—are called the “terrestrial planets” because they’re all relatively similar to the Earth.

And there are 4 more planets that are farther away from the Sun. These planets—Jupiter, Saturn, Uranus, and Neptune—are called “giant planets” because, well, they’re comparatively huge.

Where Are the Terrestrial Planets?

How far away from the Sun are the terrestrial planets? Let’s start walking to find out. With your feet on the goal line next to the coin representing the Sun, take a step or two and stop at the 1 yard line. That’s the distance at which Mercury orbits the Sun. How big is Mercury compared to the Sun? It’s incredibly tiny…because the Sun is so incredibly big! To get a sense for just how tiny, the diameter of Mercury in our scale model is a little less than the thickness of a US dollar bill.

So that’s where Mercury goes, but how about the other terrestrial planets? Take another step or two to the 2 yard line, and that’s where Venus goes. A few more steps brings you to Earth’s position about 6 inches short of the 3 yard line. And finally, a little less than mid-way between the 4 and 5 yard line is where Mars orbits the Sun.

How big are these planets? Not much bigger than Mercury in comparison to the Sun. The diameter of Mars would be a little more than the thickness of a US dollar bill in our model, and the diameters of Venus and Earth would be about the same as the thickness of two US dollar bills.

Where Are the Giant Planets?

Now, things start to get interesting. As we’ve seen, the inner terrestrial planets are all located relatively close to the Sun—after all, we haven’t even made it to the 5 yard line. But the outer giant planets are much more spaced out (no pun intended.) 

The giant planets orbit far, far away from the Sun

To get to Jupiter, we have to take a little walk to just shy of the 15 yard line. To get to Saturn, we need to walk to the 27 yard line. And then it’s time to really start walking, because to get to Uranus, we need to walk to around the 45 yard line on the other side of the half way line. And Neptune? Amazingly, you have to walk all the way to about the 15 yard line on the opposite side of the field from the Sun. As you can see, the giant planets orbit far, far away from the Sun—and their orbits are, comparatively, very widely separated.

In our model, the diameter of Jupiter is a little less than the thickness of two US dimes stacked on top of each other. Saturn’s diameter is a little smaller—about the thickness of a US nickel. And Uranus and Neptune’s diameters are a little less than the width of a US dime.

Compared to the diameters of the terrestrial planets (which were all measured in terms of the thickness of a US dollar bill), these sizes are huge—that’s why they’re called “giant” planets. But compared to the size of the Sun—whose diameter, remember, is equal to the diameter (not the thickness) of a US quarter—even these giant planets are tiny.

Wrap Up

OK, that’s all the math (and Solar System astronomy) that we have time for today.

Please be sure to check out my book The Math Dude’s Quick and Dirty Guide to Algebra. And remember to become a fan of the Math Dude on Facebook where you’ll find lots of great math posted throughout the week. If you’re on Twitter, please follow me there, too.

Until next time, this is Jason Marshall with The Math Dude’s Quick and Dirty Tips to Make Math Easier. Thanks for reading, math fans!

Solar System and football field images courtesy of Shutterstock.