The solar system

Billions of stars far, far away, but one of them is different. We don't even think of it as a star most of the time - the sun. The sun with the planets and other stuff that orbits around it make up our local neighborhood in the universe - our solar system. See how all the planets orbit the sun as if spinning on an imaginary disc? We call this disc the ecliptic plane.

Our solar system can be split into two areas - the inner and outer solar system with four planets in each. Closest to the sun is Mercury, the tiny little planet. Without an atmosphere protecting it, nothing regulates Mercury's weather. It ranges from extreme heat to extreme cold. There's no way anything could live there.

Venus is second from the sun and nearly the same size as earth. Venus does have an atmosphere, but it is thick and toxic so you won't find anything living there either. Earth has breathable air, water, and an atmosphere to regulate the temperature. The next one is the red planet - Mars. Mars has probably had liquid water, but it dried up a long time ago.

There are no traces of even the simplest forms of life on Mars. The atmosphere is too thin to support liquid water or provide breathable air. These four planets - Mercury, Venus, Earth and Mars - are dense and rocky with solid surfaces. They are terrestrial planets. The four planets of the outer solar system are composed mainly of gas and are much larger than the terrestrial planets.

They are gas giants. As gas giants, they don't have solid surfaces. Jupiter is the largest planet in our solar system. It has so much mass that it exerts a force of gravity more than twice as strong as what we experience on earth. Beyond Jupiter is Saturn with its magnificent rings.

They are made of pieces of rock and ice, held together by Saturn's gravitational force. All gas giants have rings, but none are as beautiful and visible as Saturn's. Uranus is the seventh planet from the sun. It makes a full orbit around the sun in 84 years and revolves around its own axis in 17 hours. But Uranus is tilted, so most parts of the planet have no normal day and night, but a polar night of 42 years.

Furthest from the sun is Neptune, a cold, dark, and stormy planet. We don't know much about it as it is so far away. Here's the distance from the sun to Neptune with all the other planets. It takes sunlight eight minutes to travel from the Sun to Earth. To Jupiter, it's 43 light minutes.

But that's nothing compared to Neptune. A beam of light from the sun takes four hours before it hits the gas surface of Neptune. Distances are so vast that we can't even see the planets. Comparing sizes, we have to ignore distances. Jupiter, the biggest planet, has a diameter more than ten times bigger than Earth's.

And the sun's diameter is ten times bigger than Jupiter's. And there are smaller objects in our solar system. There are dwarf planets like Pluto and this chunk of rock and ice - a comet. Comets orbit the sun and start melting as they get closer, releasing a tail of burning gases. The tail is pushed by the sunlight in the direction away from the sun. Between the inner and outer solar system, you'll find a broad belt of rocks and fragments of planets - asteroids.

Asteroids are much smaller than planets. Even smaller pieces of rock and metal can be found throughout the solar system. When a rock is pulled into our atmosphere by Earth's gravitational force, the air resistance heats it up and makes it burn appearing like a star shooting across the sky - a meteor. Most meteors burn up completely before they hit the ground. But sometimes, a piece of burned rock or metal hits the ground - a meteorite. It's a rare occasion when you get to meet a visitor from another part of our solar system like that.

The solar system is made up of all the stuff that is orbiting the sun - the planets with their moons and rings, the asteroids, comets, and heaps of dust and rocks, and bits of planets that have broken loose from collisions in space. All of it makes up our local neighborhood in space - our solar system.