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  The Milky Way Galaxy:  
 

 

The Greeks had called it Kiklios Galaxios (milky circle). The Romans had dubbed it Vic Lactea or “Milky Way.” Today, we of course know it by the same name: The Milky Way Galaxy, home to Earth’s Solar System.

Stars, Dust, and Gas
The Milky Way is one galaxy of billions of galaxies in the observable universe. Its classification is a “barred spiral galaxy” and features six arms extending out in logarithmic spiral shape. If seen as a whole, the galaxy’s overall appearance is similar to that of a hurricane eye or nautilus seashell. The Milky Way is composed of stars, dust, gas, and dark matter.

It is a member of the Local Group of galaxies, which is comprised of some 30 galaxies. Of course, the Milky Way is of special interest to us, as it is the home of our Solar System. Precisely, we exist in the Orion Arm – a small, partial arm of the galaxy found between the Sagittarius Arm and Perseus Arm.

The major spiral arms of the Milky Way are (from closest to furthest):

• Norma Arm
• Scutum-Crux Arm
• Sagittarius Arm
• Perseus Arm

In addition, the two minor arms are the Orion Arm and the Cygnus Arm, which is found on the other side of Perseus.

Being part of such a vast space, one can imagine how difficult it had to be for early astronomers to figure out our place within it. From Earth, the Milky Way appears as a white swath in the night sky. Yet we’re still only seeing a small part of its composition. To put this in perspective: the Milky Way’s stellar disk is believed to measure 100,000 light years in diameter.

 

 
  Discovery & Collision Course:
  Stargazers have been fascinated by the Milky Way’s white band for centuries. What exactly was it? And how did it relate to our own planet?

Greek philosopher Democritus (460-370 BC) is often credited with discovering the Milky Way, discerning that the illuminated band in the night’s sky was actually billions of distant stars. Aristotle (384-322 BC) noted the philosopher’s theory, but proposed one of his own, in which he believed it was stars burning up in the Earth’s atmosphere that created the glow.

Some 2000 years later, Galileo Galilei would use his telescope to confirm that indeed, the Milky Way was composed of distant stars. But just how many? Try 200 billion stars and quite possibly, a more accurate number would be closer to 400 billion stars!

The two biggest galaxies in the Local Group are the Milky Way and the Andromeda Galaxy. There is a theory that in approximately 4.5 billion years, these two galaxies will “collide.” If so, they will likely end up creating one humungous, new galaxy.