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# How Big Is the Solar System?

How big are the planets of the Solar System compared to the enormous Sun at its center? How far would you have to travel to reach each of them? And how can you build your own scale model of the Solar System to see all of these relative sizes for yourself? Keep reading to find out!

By
Jason Marshall, PhD,
July 29, 2016
Episode #205

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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..

## 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.

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