Our Neighborhood in the Universe
Within the Milky Way galaxy, orbiting one yellow star called "sun", there are nine planets.
Nine planets? Sun? Sounds familiar? We're talking about our solar system, located in one of the spiral arms of the Milky Way galaxy. The solar system is our neighborhood.
It may be small, but it's fascinating and very special.
Everything Revolves Around the Sun
All bodies in the solar system orbit the sun. They are trapped in orbit by the sun's strong gravity. Of course, the orbits are not really marked in the heavens! They are drawn here only to demonstrate the planets' motion. The plane in which the planetary orbits lie is called "The Ecliptic Plane". Only Pluto's orbit is tilted with respect to the ecliptic plane.
The Size of the Solar System
How do we determine the size of the solar system? After all, it's not just one body, like a planet or a moon, which can be measured accurately.
The size of the solar system is usually measured according to its boundaries. Astronomers consider the orbit of Pluto to be the boundary, because it is the planet farthest from the sun.
This makes the diameter of the solar system approximately 80 astronomical units, or about 7.5 billion miles (12 billion kilometers).
4.5 Billion Years Young
How old is the solar system?
Scientists believe that all the bodies of the solar system formed at the same time, so their ages are identical. The entire solar system is approximately 4.5 billion years old.
How Did the Solar System Form?
The accepted theory is that the formation of the solar system was a long and complex process. Not all of it is completely understood,and many questions are still unanswered.
1- First, an interstellar cloud of dust and gas contracts. In the center of the cloud, a new star is born - our sun.
2- The cloud rotates and becomes a flat disk. Our sun glows in the center.
3- The particles of dust in the disk adhere to each other. They combine to form little lumps of matter. These lumps form a base on which more matter can accumulate. Around the sun, whirlpools begin to form.
4- Inside the whirlpools matter begins to collide & stick together, creating growing lumps called planetismals. These lumps move in regular orbits around the sun.
5- The large lumps attract remnants from the whirlpool, forming planets. The leftovers form the moons, asteroids, and comets. Still, a lot of debris remains scattered throughout interplanetary space.
