HowDoWhy

Measuring the dimensions of our solar system brings up a question of preference. Are you interested in the diameter from the Sun to the outermost planet? To the innermost edge of the Kuiper Belt? To the outermost edge of the belt? To the Oort Cloud? Would you fully grasp the true scale even were I to answer any of the above? Likely not. Distances and scale in the solar system are so tremendous that, unless you create a physical model, you’ll never really understand just how large an area we’re talking about. Maybe we should put it all into perspective when we’re done.

Most of us think of the solar system as the sun and its planets so we’ll make that our first measure of distance. As mentioned in a previous post - Weren’t there 9 planets? What happened to Pluto? - Pluto has lost its planetary status so that makes Neptune the furthest planet from the Sun at about 2.79 billion miles or 30.07AU. AU stands for Astronomical Unit and is a means of measurement already discussed in my post - What is an Astronomical Unit. Remember, that’s a radial distance (from the center to the edge). The diameter of the solar system as measured to the outermost planet is twice the radius or 5.58 billion miles (60.14AU).

But the solar system isn’t just limited to its planets. There are also the Kuiper Belt objects such as Pluto. These have been measured in as close as 31.7AU and as far out as 48AU. The general inner edge of the Kuiper Belt is accepted as 30 AU (closer in than even Neptune’s elliptical orbit) and as far out as 50 AU. In miles, that equates to 2.79 billion miles and as far out as 4.65 billion miles.

But why stop there? The real edge of our solar system, where the Sun’s gravity loses dominion over its surroundings, is the Oort Cloud. The Oort Cloud is estimated to reside in a sphere about 18 trillion miles out from the Sun. That’s 18,000,000,000,000 miles or 193,548.38 AU. Think about that… if you made the trip from the edge of the Sun to the Earth and some wise guy in the back seat shot off his mouth and convinced everybody to, “just keep driving till we hit the edge of the solar system,” you’d have to repeat the trip you just made over 193.5 thousand times more before you reached your destination.

Well, there you have your straight forward numerical answers but, as I implied before, wrapping your head around what those numbers really mean is just impossible without some kind of example or model. So if you’d like some common examples, read on!

I’ve enjoyed using walking, driving and flying examples in previous posts to show just how far away planets are from the Sun, but at the distances we’re talking now, things really get crazy. The smallest example in our solar system size analysis was 2.79 billion miles to Neptune. To fly there on a Boeing 747 would take you just shy of 559 years. To be arriving today you’d have had to depart before Leonardo da Vinci hypothesized and sketched a parachute. To walk there at a man’s average pace would take you just shy of 91,000 years. To be arriving today you’d have had to have left tens of thousands of years before the first cave paintings, before intentional burial and even before humans entered Europe! Mammoths would have been thriving when you left. And that’s just to get to the closest “edge” of our solar system.

Flying to the outer edge of the Kuiper Belt in a 747 would take over 931 years.

But here’s where we really blow your mind. Flying to the true outer edge of our solar system, the Oort Cloud, would take 3.6 million years.

To put the full size of the solar system into a measurement you might understand, let’s shrink it by a really big number… let’s make the solar system a billion times smaller than it really is. Now, a trip from the Sun to Neptune is just 2.79 miles. You could walk there in under an hour. But if you wanted to walk to the Oort Cloud, you’d have a trip of 18,000 miles ahead of you and it would take you (non-stop) about 5142 hours or 214 days to reach your destination.

If you shrunk the solar system by 100 billion, (100,000,000,000) the planets would fit into something recognizable. In fact, the distance from the Sun to Neptune would be just shy of half a football field in length. The entire planet Earth would be less than ½ a millimeter in diameter. The edge of the Oort Cloud, however, would still be 180 miles away.

I hope you’ve gathered the true immensity of the solar system by reading this post. Keep these sizes in mind as we move on from here and eventually get into some really big objects and distances as we discuss galaxies!