 |
| Universe |
|
| Universe consists of all matter and all light and other forms of radiation and energy. It consists of everything that exists anywhere in space and time. |
| |
| The universe includes the earth, everything on the earth and within it and everything in the solar system. |
| |
| All stars, including the sun, are part of the universe. Some other stars also have planetary systems. In addition to planets and stars, the universe contains gas, dust, magnetic fields and high - energy particles called cosmic rays. |
| |
| Stars are grouped into galaxies. The sun is one of more than 100 billion stars in a giant spiral galaxy called the Milky Way. |
| |
| Galaxies tend to be grouped into clusters. Some clusters appear to be grouped into super clusters. |
| |
| No one knows whether the universe is finite or infinite in size. Studies of the sky indicate that there are at least 100 billion galaxies in the observable universe. |
| |
| According to the Big Bang theory, it is belived that a huge explosion took place about 15 billion (15 x 109) years ago, and since then, the universe is expanding. |
| |
| But, according to the steady state theory, the universe is unchanging. It did not have a begining and will not have an end. |
| |
