How Big Is the Universe?

The solar system is big, the distances between stars bigger, and the distance to the center of the galaxy in which we live is even bigger than that. But all of that is tiny compared to the distance to the edge of the known universe! Just how big is that? The Math Dude breaks it down.

Jason Marshall, PhD,
July 25, 2014
Episode #206

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As we learned last time, the solar system is an almost unfathomably vast place. But compared to the rest of the universe in which we and everything else live, the solar system is actually rather quaint and cozy. Because the universe is not just almost unfathomably vast—it's truly unfathomably vast.

But that's not going to stop us from trying to come to grips with exactly how big it is! Just as we did last time with the solar system, today we're going to build a scale model of the entire universe to help us get a better feeling for the immensity of the numbers behind it..

Recap: How Big Is the Solar System?

Solar SystemBefore we head for the stars, let's quickly recap what we learned last time about the size of the solar system. In a nutshell, we learned that the solar system—which consists of our friendly neighborhood star (the Sun), Earth, the seven other planets, as well as a bunch of comets, asteroids, and other fun stuff—is really, really big.

To get a feel for just how big, we imagined shrinking the Sun down by a factor of 57.3 billion to the size of a US quarter coin, and then placing this model Sun on the goal line of a 100 yard long American football field. In this model, the planet Mercury sits at about the 1 yard line, the planet Venus sits at the 2 yard line, Earth sits just short of the 3 yard line, and Mars sits between the 4 and 5 yard lines.

To get to the giant planets in the outer solar system, we have to start hiking. On this football field, Jupiter sits at about the 15 yard line, Saturn sits at the 27 yard line, Uranus sits at the 45 yard line on the other side of the field, and Neptune is way down at the 15 yard line on the opposite side of the field from the Sun. Remember, we Earthlings are only about 3 yards away from the Sun at this scale. So Neptune is really far away!

How Far to the Stars?

Here's where things start to get a little crazy. The truth is that the incredibly long distance between the Sun and Neptune is really only "incredibly long" when we're talking about sizes within our solar system. Because as soon as we step out of those friendly confines, and instead think about the distances to the stars, we see that Neptune is, comparatively, right next door.

To see what I mean, let's take a look at the closest star outside of our solar system: Proxima Centauri is one of a trio of stars orbiting each other in a group known as Alpha Centauri. How far away is this star? It's about 24.8 trillion miles away from Earth. That sounds like a lot, but it's hard to imagine just how far that is when dealing with such large numbers.

So let's think about our football field scale model. On that model, where the Sun sits on one goal line and Neptune sits at the 15 yard line on the opposite side of the field, Proxima Centauri would be about 433 miles away. There is a lot of space out there between the stars!


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