# How Big is the Solar System?

I'm standing under one of austin's famous moontowers. At the end of the 19th century to recreate moonlight in this growing city.

The moon is the brightest thing in the night sky, but most people don't really understand just how far away it is. Derek from veritasium did an awesome video about this, so you should go check it out.

The moon is actually 385,000 km away. That's really far. Distances are a funny thing. You can picture the distance from your house to the corner, or from your hometown to where your grandma lives.

But beyond that, the human brain just can't fathom the scale of the solar system . Just how far apart and tiny everything is! So just how big is the solar system? Let's make this grapefruit the sun.

It's orangey and round like the sun is. It's about 110 millimeters in diameter, compared to 1.39 million kilometers for the actual sun. We'll put it here, at the center of our solar system.

And here we are at our first planet, mercury. one thing to note about the orbits of the planets, they aren't circles, they're ellipses. That means sometimes they're a little closer and sometimes they're a little farther.

Here we are 4.5 meters or about 15 feet from the grapefruit sun back there. On this scale, mercury is only the width of just 4 human hairs.

At 59 million kilometers from the sun, it's really hot here. It's close enough to burn away nearly all of its atmosphere. And here we come to venus, we're about 8.5 meters away from our grapefruit sun, which is 108 million kilometers.

From here venus is just under 1 mm wide, the same thickness as about ten sheets of paper, stacked together. Next we come to earth, this 1 mm blue dot, that's here, that's home, that's us.

As carl sagan said. We are about 11.6 meters from our grapefruit sun, which is the same as 150 million kilometers. It takes light from the grapefruit 8 and a half minutes to get to this point.

We call that one astronomical unit. There's something very special about this zone. Because of this particular distance from the sun, and the geologic and atmospheric qualities of earth, this habitable zone is what makes life possible here on our planet.

Next we come to the red planet, mars. We're about 18 meters out now, which is the same as 229 million kilometers, sitting in the orbit of mars.

At this scale, mars is a tiny 0.5 mm red dot, the same width of a human egg cell. Next we find ourselves in the asteroid belt, this stretches about 23-46 meters from our grapefruit center over there.

Movies get the asteroid belt all wrong. If you clumped it all together, it would only be about 4% the mass of our moon. That means it would be the same as a grain of salt, crushed up and distributed around this entire orbit.

Here we are at jupiter, the largest planet in the solar system. It's 143,000 kilometers in diameter, but on our scale it's just bigger than a centimeter. We are about 61 meters out here, the same as 779 million kilometers.

Here we are at saturn, my favorite planet. now we're about 112 meters out here, and at this scale, saturn is only about the height of a lego brick.

Now we come to the first of the ice giants, uranus. We are really far away. We are 226 meters from where we started, which is the same as 2.9 billion kilometers from the sun. That's over twice as far as we just were at saturn.

Now, out here, uranus is only 3.7 millimeters wide, and temperatures are so cold that they can reach down to -224 degrees celcius. Here we are at neptune, the outer ice giant. now we're more than 350 meters from where we started, that's more than 4.5 billion kilometers. out here, I can't see the sun, I can barel; y see uranus.

That's actually how neptune was discovered. We couldn't see it, it looked like another star in the sky, if it hadn't been for it's gravitational effect on its neighboring planet, we never would have found it.

It orbits so slowly out here that it's only circled the sun once since we discovered it in 1846. Well, I guess that's all the planets! But we can't forget about this guy, pluto.

Now we all know that pluto's not officially a planet anymore and there's some good reasons for that. We just entered a region of the solar system called the kuiper belt.

These are frozen remnants of the early solar system, icy rocks that have come together, frozen methane and ammonia. Pluto is so small, that out here, it would be the width of a single dollar bill.

And instead of being flat in its orbit like the rest of the planets, it's kind of tilted up on an angle. It's so elliptical, that for 20 out of its 250 year orbit, it's closer to the sun than neptune is.

But I know how strongly you guys feel about pluto, and while we can't call it a planet, we'll go ahead and put it out here. If you'd like to play with your own solar system model, I put some links down in the description so you can do your own calculations and make your own.

I'd love to see them, so email me, send them to me on facebook, twitter, all those links are down below too. Hopefully this gives you an idea of just how big the solar system really is.

That might make some of you feel kind of small, but it shouldn't, because we're the ones that are able to figure all of this out, and explore to the farthest reaches of the solar system.

And maybe one day, beyond. That makes me feel pretty tall. One more thing! Voyager was launched in 1977, a craft the size of a car, shot out to the outer reaches of the solar system.

Right now it's more than 18.5 billion kilometers from the sun. That's it. This is the edge. It's the equivalent of standing 1.4 kilometers from our grapefruit. It's the farthest manmade object from earth.

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