Saturday, June 1, 2013

Galaxies

The Milky Way galaxy is most significant to humans because it is home sweet home. But when it comes down to it, our galaxy is a typical barred spiral, much like billions of other galaxies in the universe. 

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 things, the band has been visible in the heavens since Earth first formed. In reality, this intriguing line of light is the center of our galaxy, as seen from one of its outer arms. The Milky Way is a barred spiral galaxy, about 100,000 light-years across, contains over 200 billion stars, and enough dust and gas to make billions more.

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 the 4.5 billion year old sun.

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 suspects.

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, that astronomers realized that the fuzzy patches once classified as nebula were actually separate galaxies.

If you could look down on it from the top, you would see a central bulge surrounded by four large spiral arms that wrap around it. Spiral galaxies make up about two-third 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.


from AmazingUniverse.info