The words solar system refer to the sun and all of the objects that travel around it -- planets, natural satellites such as the moon, asteroid belt, comets, and meteoroids. Our solar system is part of a spiral galaxy known as the Milky Way. The sun, the center of our solar system, holds eight planets and countless smaller objects in its orbit.

10 Need-to-Know Things About Our Solar System:

1. Our solar system is made up of the sun and everything that travels around it. This includes eight planets and their natural satellites such as Earth's moon; dwarf planets such as Pluto and Ceres; asteroids; comets and meteoroids.

2. The sun is the center of our solar system. It contains almost all of the mass in our solar system and exerts a tremendous gravitational pull on planets and other bodies.

3. Our solar system formed about 4.6 billion years ago.

4. The four planets closest to the sun -- Mercury, Venus, Earth, and Mars -- are called the terrestrial planets because they have solid, rocky surfaces. Two of the outer planets beyond the orbit of Mars -- Jupiter and Saturn -- are known as gas giants; the more distant Uranus and Neptune are called ice giants.
5. Most of the known dwarf planets exist in an icy zone beyond Neptune called the Kuiper Belt, which is also the point of origin for many comets.

6. Many objects in our solar system have atmospheres, including planets, some dwarf planets and even a couple moons.

7. Our solar system is located in the Orion Arm of the Milky Way Galaxy.

8. There are most likely billions of other solar systems in our galaxy. And there are billions of galaxies in the Universe.

9. We measure distances in our solar system by Astronomical Units (AU). One AU is equal to the distance between the sun and the Earth, which is about 150 million km (93 million miles).

10. NASA's twin Voyager 1 and Voyager 2 spacecraft are the first spacecraft to explore the outer reaches of our solar system.