# Wikijunior:Solar System/How the Solar System was born

Our **solar system** is part of an entity called our **universe**. There
were many attempts made in the past to explain how our solar system and
universe came into existence as we observe it today. Most scientists use
the **Big Bang Theory**, though some people have other theories.

## Big Bang Theory

This theory is based around the idea that an enormous explosion occurred
about 13.7 billion years ago. That is 13,700,000,000 years ago. This is
three times the age of Earth! The Big Bang was not a usual explosion in
space because space and time themselves were made in the explosion. This
explosion caused the formation of the matter and energy in the universe.
At first, the universe was very hot. The planets, stars and all other
heavenly bodies formed starting some time after the Big Bang after the
universe had cooled down.

The universe had been expanding and cooling since the Big Bang. Most
galaxies are moving further away from our Milky Way galaxy. The
exceptions are the few galaxies that are close enough to the Milky Way
for gravity to overcome the universe\'s expansion.

Scientists can still see the faint light from when the universe was hot.
Over time, the universe\'s expansion stretched out the light, turning it
into weak microwave light. Scientists can detect this microwave light.

## Milky Way Galaxy Formation

## Solar System Formation

The solar system formed out of a big cloud of gas and dust about 4.6
billion years ago.

thumb\|250px\|Eagle Nebula (M16) - Birth of New
Stars

Stars and solar systems that are very similar to the Sun are now forming
in the Eagle Nebula (also known as M16). While this is not a picture of
our own sun, it can give you an idea of what our solar system looked
like billions of years ago. These gas clouds that you see in this image
were formed from earlier stars that exploded and left stuff behind.

Small finger-like parts of these clouds, especially at the \"top\" of
the first column on the left, are the new stars that are forming.
Astronomers who have been watching these stars form have seen changes
happen in just a few years, which is a very rapid change for the life of
a star. Over many millions and billions of years, these stars and any
planets formed with them will look like our Solar System today.

What astronomers think happened after this initial period when the Sun
was created from these huge gas clouds, there were many small and large
rocks that gradually came together because of gravity and formed the
planets, moons, asteroids, and comets that we know about today. Many of
the craters which can be found on the Moon were made when these rocks
came crashing on to the surface.

While the number of small rocks and other stuff from the early history
of the solar system is now less than what it was like right after the
Sun formed, the space between the planets still has many of these rocks,
and they continue to form craters and even come into the Earth\'s
atmosphere. When you see these rocks at night, they are known as either
**Shooting Stars** or **Meteorites**. By watching these items come to
the Earth, you are directly witnessing the process that created the
Earth in the first place.

