Our Solar System

Our Solar System

Planets are big balls of rock or gas that move around stars. We live on one we call the Earth, which moves around a star we call the Sun. There are at least seven other planets moving around the Sun and a lot of other smaller things as well. All these things together are called a system. The Latin word for the Sun is Sol, so we call this system the Solar System.

A long time ago, people didn't realize that all these things in the Solar System move around the Sun. They thought everything moved around the Earth, including the Sun. This seems sensible, because the Earth doesn't feel as if it's moving, does it?

About 500 years ago, however, a man named Copernicus suggested that all the planets moved around the Sun.[1] Then, about 100 years later, a man called Galileo began looking at the sky with a new invention: the telescope. He showed that it was very likely that all the planets moved around the Sun. Soon, more and more people started using telescopes to study the sky. They began to learn how the planets and the other things in the Solar System moved.
Now, we send rockets into space to learn more. Astronauts travel around the Earth. Some of them have landed on the the Moon. Robots can fly to other planets to take pictures. We can see things that people like Copernicus and Galileo could only dream about.

We can use very large telescopes to see what has happened to other stars. We compare pictures of distant stars with pictures of the Sun. We can use thousands of pictures of the planets to learn more about Earth. We use what we learn about all the things in the Solar System to figure out how it was formed.
A long time ago, people didn't realize that all these things in the Solar System move around the Sun. They thought everything moved around the Earth, including the Sun. This seems sensible, because the Earth doesn't feel as if it's moving, does it?
About 500 years ago, however, a man named Copernicus suggested that all the planets moved around the Sun. Then, about 100 years later, a man called Galileo began looking at the sky with a new invention: the telescope. He showed that it was very likely that all the planets moved around the Sun. Soon, more and more people started using telescopes to study the sky. They began to learn how the planets and the other things in the Solar System moved.
Now, we send rockets into space to learn more. Astronauts travel around the Earth. Some of them have landed on the the Moon. Robots can fly to other planets to take pictures. We can see things that people like Copernicus and Galileo could only dream about.

Our Solar System
The Sun
Mercury
Venus
Earth
Moon
Mars
Asteroid belt
Jupiter
Saturn
Uranus
Neptune
Pluto
Comets
Kuiper Belt
Oort Cloud
Glossary
We can use very large telescopes to see what has happened to other stars. We compare pictures of distant stars with pictures of the Sun. We can use thousands of pictures of the planets to learn more about Earth. We use what we learn about all the things in the Solar System to figure out how it was formed. We can also guess what might happen to it in the future.

What is the Solar System?
At the center of the Solar System is the Sun. It is a star, like the billions of other stars in the sky. The other stars are very, very far away, so they look tiny. The Sun is important to us because it gives us heat and energy that allows life. None of the life on Earth could exist without the Sun.
The rest of the things in the Solar System orbit (travel around) the Sun. The planets are the largest of these. Each planet is a little like the Earth. But the planets are also very different from each other.
Many of the planets have moons. A moon orbits a planet. Mercury has no moons. Earth has one. Jupiter has 63!
The planets closest to the Sun are called the inner planets. These are Mercury, Venus, Earth, and Mars. Then comes a big ring of asteroids, chunks of rock much smaller than planets. This ring is called the asteroid belt. Within the asteroid belt, there is a dwarf planet named Ceres. Then come the outer planets: Jupiter, Saturn, Uranus, and Neptune. Farther out there are two dwarf planets, Pluto and Eris.
Beyond the orbit of Neptune is another big ring of things like the asteroids, called the Kuiper belt. Kuiper (said "KYE-per") was the last name of the person who first wrote about it. Most of the things in the Kuiper belt are hard to see through telescopes.
After the Kuiper belt comes the Oort cloud. Scientists think this is where comets come from. It is very far away, many times farther away than Pluto is from the Sun (over a thousand times). It is near the edge of the Solar System.(Yes, "Oort" was the last name of the person who first wrote about it.)In between all the other things is dust. The pieces of dust are very far apart, but they shine in the light of the Sun. Before dawn, in September or October, they glow in the East. We call this the zodiacal glow.
When pieces of space dust hit the Earth's atmosphere, they burn brightly. We call them shooting stars or meteors.
The Sun creates solar wind—a kind of gas that blows away from the Sun into space. This gas travels out past the planets into outer space. The edge, where the solar wind meets the wind from other stars, is called the heliopause. That is about 100 times as far from us as the Earth is from the Sun. Beyond that is a lot of empty space. The nearest star to our Sun is thousands of times farther away than the size of the entire solar system. The Universe is a really huge place!

What holds it together?

Why do all of the planets orbit the Sun? Why do moons orbit planets? Why doesn't the Sun move off and leave the planets behind? The answer to all of these questions has to do with gravity. Gravity is a force that is a property of mass. It pulls things together.
We don't notice the pull from the Sun because it also pulls on the Earth by the same amount. But the Sun's gravity is strong enough to keep the Earth from shooting away. Even though the Earth is going fast, it keeps turning to go around the Sun. It is like they were tied together with an invisible string. In the same way, moons orbit many of the planets. They are kept there by gravity. The Sun itself does not sit still in space. The entire Solar System is orbiting the center of our galaxy. The whole thing stays together because of the force of gravity.