A glance up at the night sky reveals a broad swath of light. Described by the ancients as a "river," as "milk," and as a "path," among other descriptions. This astronomical band has been visible in the heavens since Earth first formed. This intriguing line of light is the center of our galaxy, as seen from one of its outer arms. The Milky Way is approximately 100,000 light-years across, contains over 200 billion stars, and enough dust and gas to make billions more (1 light-years is5.88 trillion miles).
The solar system lies about 30,000 light-years from the galactic center, and about 20 light-years above the plane of the galaxy. More than half the stars found in the Milky Way are older than our sun, estimated to be 4.5 billion years old.
The most common stars in the galaxy are red dwarfs, a cool star about a tenth the mass of the sun. Once thought unsuitable for potential life-bearing planets because such bodies would have to be too close to meet the criteria, red dwarfs are now considered potential 'goldilocks planets' (not too close, not too far, but just the right distance to its closest star for life to form and thrive).
As late as the 1920s, astronomers thought all of the stars in the universe were contained inside of the Milky Way. It wasn't until Edwin Hubble discovered a special star known as a Cepheid variable, which allowed him to precisely measure distances. Astronomers then realized that the fuzzy patches once classified as nebula were actually separate galaxies.
An aerial view of the Milky Way, you would see a central bulge surrounded by four large spiral arms wrapped around it. Spiral galaxies make up about two-thirds of the galaxies in the universe. Unlike a regular spiral, a barred spiral contains a bar across its center region, and has two major arms. The Milky Way also contains two significant minor arms, as well as two smaller spurs. One of the spurs, known as the Orion Arm, contains the sun and the solar system. The Orion arm is located between two major arms, Perseus and Sagittarius.
The Milky Way does not sit still, but is constantly rotating; as such, the arms are moving through space. The sun and the solar system travel with them. The solar system travels at an average speed of 515,000 miles per hour (828,000 kilometers per hour). Even at this rapid speed, the solar system would take about 230 million years to travel all the way around the Milky Way. Consider the fact that the Andromeda Galaxy, our closest heavenly neighbors, sits 2.5 million light-years away - about 15 quintillion (15,000,000,000,000,000,000) miles from Earth - it's no wonder we have not found intelligent life in the universe.
from AmazingUniverse.info
