Teaching the Solar System

We all grew up with a pretty simple idea of the solar system, right? There were nine planets moving in circles around the sun. Some were big and some were little but in the pictures they were all evenly spaced out and lined up. The problem is, it's not right. They aren't moving in circles (they move in ellipses), they aren't evenly spaced, and it turns out there aren't even nine of them! To top it all off, the solar system has parts most of us haven't even heard of.


Probably the first thing to learn is the distances involved. Distances in space are measured in two different ways. Outside the solar system, we measure the distance between stars in light years (how far light can travel in a year). But inside the solar system, that measurement is too big. It's like trying to measure how big your living room is by using miles. Instead, distances in the solar system are commonly measured in Astronomical Units (AU). An AU is simply the average distance between the Earth and the Sun. The sun is 1 AU from the earth.


A really good way to start learning how far apart things in space are is to map out the solar system. This is a super easy activity for parents, and it'll help your kids (and you) get a real grasp on what the solar system is actually like.


Here's what you need:


1. Planets. No, don't go out and buy styrofoam balls or anything. I've found that pictures work really well. You can order a really nice lithograph set from NASA... or you can just have your kids get out their crayons. Either way works great.
2. A long room or hallway. It needs to be at least 50 feet long.
3. string
4. tape
5. A way to measure the distances. A tape measure is fine (as long as it's a bigger one that will measure the entire 50 feet). Another easy way to measure it is to use a hallway in a public school. Most schools have linoleum tiles on the floor that are one foot squares. Just count the tiles to measure your distance.


And here's what you do:


Step 1.
Have your kids draw a picture of the sun and of each planet. It's OK if they don't know anything about the planets yet. This is part of how they learn. If they don't know any of the planets, tell them the names and let them use their imaginations. "Let's draw Jupiter! It's the biggest!" is fine. Don't worry about it if the planets are the wrong color or size. It'll be fine. Do be sure to include Pluto even though it's not a planet anymore. This is a great way to show how it's not like the other planets.


Step 2.
Have them tape the picture of the sun at one end of the hall. Then tell them to guess where the planet that's closest to the sun is. Have them tape Mercury on the wall where they think it belongs. Next comes Venus, then Earth, Mars, an Asteroid Belt (bet you didn't know we had one!), then Jupiter, Saturn, Uranus, Neptune, and Pluto. Most kids (and adults) will naturally space the picures out on the wall instead of clump them together.


Step 3.
Walk back over to the "Sun" and tell your kids that most people (even grown-ups) don't realize how far apart things really are in space. So you guys are going to re-hang their pictures but this time we'll see if we can get them the right distance apart. So you start measuring. And as you measure and move the pictures, you talk:


"Let's just pretend that the Earth is one foot away from the sun. So let's hang it's picture here... So every one foot is an Astronomical Unit. That sounds fancy, but it just means how far it is from the Sun to the Earth. Just like if we measured how far our house is from the road, we could call it a Yard Unit and measure everything that way. So... if the Earth is one AU (Astronomical Unit) from the Sun, then we need to fit a few other planets between the sun and the Earth."


Just talk them through the process of putting the pictures where they belong. Kids get a real kick when they realize that the first few planets are all scrunched together and the others get further and further away.


Here are the measurements for you:
















As you rearrange the pictures, be sure to talk about how big each planet is. The sun is huge in comparison to everything else. If the Earth is the size of a marble, the sun is as big as a house. The entire wall that your picture of the sun is hanging on isn't large enough to put it in scale.

When you get to Pluto, there's a big "Huh???" moment. It has a range. So you stare at the wall a few minutes and talk about it. "It could be as close as this. But it could be as far as that!" Eventually, someone (maybe you) will decide to cut a hole in the picture and thread it on a string. Tape one end of the string to the wall at 30 feet from the sun, and the other end at 49 feet. Then the kids can slide Pluto around to all the places it could be. "Holy cow! It can be just as close as Neptune! It can even be a little closer? What the heck?" Want to get even stranger? It's orbit isn't level with the other planets. The other planets orbits are in a disc, kind of like the rings of Saturn. Pluto's orbit is tilted so that it goes above and below the disc. Plus there's a lot of debris in it's orbit. It still bumps into things as it travels around the sun. And it's a lot bumpier than the other planets. Those are the reasons it's no longer considered a planet. (For sentimental reasons I disagree and still count it as a planet, but it's definitely different from the others.)


Step 4.
So now you've hung all of your planets (+1 extra planet and a bonus asteroid belt) on the wall. What's next? The other stuff that you didn't know about.


Just after the planets there's a place called the Kuiper Belt. It overlaps the outermost planets and goes all the way out to 100 AU from the Sun. That's twice as far out as Pluto gets! The string it would take to show it's range is as big as the rest of the solar system. It also contains at least one dwarf planet - Pluto. Pluto is now considered to be a member of the Kuiper Belt - the largest object belonging to it, in fact! But it's not alone out there. There are comets and other icy rocks there, too. And there's more stuff beyond it. There's another dwarf planet calle Eris at 97 AU. It's right at the start of something called The Scattered Disc, which is just a big (huge!) disc with tiny icy planet-y rocks scattered in it. It goes out even further and has a bigger range.


And there might even be more. Scientists think there's something called an Oort Cloud, named for the guy that imagined it. (Imagination is good!) Scientists know that some comets travel far past the planets and even past the Scattered Disc. So we think those long-distance comets come from the Oort cloud that might be 50,000 or more AU from the Sun. Right now it's impossible to know because the comets move so fast and are so small. (Kind of like kids.)


If you were to draw a picture of the Oort cloud and hang it on a wall, it would be 9 and a half miles away. And the nearest star is 271,000 AU from here. That's fifty-one miles away from your picture of the sun!


So now you've taught your kids the basics of the planets. There's more... and it's way cool. But I'll have to dig it all up so it'll be a bit before I post it. If you have questions, let me know. And if you like what I wrote, please let your friends know and share my blog with them. I'm really enjoying meeting new folks via blogging.