Solar System

The Solar System has the Sun and things around it. These things, called astronomical objects, are in outer space. Their sizes range from millions of kilometers (the Sun, planets) to smaller than a milimeter (dust).

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  The Solar System has one star, eight planets, hundreds of moons, thousands of comets, and more than a million asteroids. Sadly, most of them are too small to be seen in this picture!

The largest thing in the Solar System is a star named the Sun. Smaller than that is the eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. One of these planets, Earth, is where we and life live. Smaller than that is the dwarf planets (the "almost planet") and small Solar System bodies (a category that has asteroids and comets). Smaller than that are the meteoroids. And finally, the smallest of these objects are dust floating in space.

Things in the Solar System are very far away from each other. It is hard for our minds to truly understand. Let's take an example. The New Horizons probe is the fastest thing ever flown from Earth, around 100 times faster than a normal jet airliner. Even at that speed, it takes 3463 days to reach to Pluto. Pluto was at 33 astronomical units away from the Sun. Some scientists think the Solar System can be as big as 100000 astronomical units away from the Sun.

Like the Earth, objects in the Solar System are very interesting to explore. Since the ancient times, humans have keep track of planets' motions when we only know them as 'bright lights moving across the dark sky'. This is the birthplace of astronomy. Nowadays, we know much more. We have built large telescopes and sending space probes to learn more about these objects. Doing so helps us to learn more about the origins of life, other star systems, and perhaps how to live on distant worlds.