Our Amazing Milky Way Galaxy

Oct 26, 2012 By Deepa Gopal
Deepa Gopal's picture

According to an ancient Greek myth, baby Heracles was brought by Zeus to Hera to drink her milk so that he would become immortal. The Milky Way is nothing but spilled milk!

Appearing as a bright band across the night sky, the Milky Way -- our galactic home, has fascinated many an astronomer. Galileo aimed his first telescope at the heavens in 1610. 

And now, thanks to a Visible and Infrared Survey Telescope in Chile's Atacama desert, we have the largest and the most detailed picture of our Milky Way galaxy. The 9-billion-pixel image is so large that if it were printed at the resolution of a normal book, it would take 9 meters by 7 meters of paper! The image shows 173 million objects, 84 million of which are stars like our Sun.

What Is A Galaxy?

Simply explained, it is a collection of millions or billions of stars, along with gas and dust that are bound together by gravity. The light from these stars is what gives a galaxy its glow. Galaxies also consist of planets, asteroids, black holes, and dark matter which gives a galaxy its shape -- elliptical, spiral or irregular.

Milky Way: A Cosmic Spiral

Did you know that our Milky Way is a breathtaking, spiral-shaped galaxy? At the center of the galaxy is what astronomers call a galactic bulge, seen in the image as a yellow core. This region is shaped like a sphere and contains the highest density of stars. Most of these stars are old and dying, which is why large black holes may also be found at the center of the galaxy.

From this center, there are arms spiraling outwards like a pinwheel, to the outer edges of the galaxy. The major arms are named for the constellations seen in those directions form our Earth. Perseus Arm, Sagittarius Arm, Centaurus Arm. But where is our solar system? In a minor arm called Orion Spur. The spiral disk is surrounded by a halo which contains clusters of older stars and dark matter.

Astronomers have figured out our exact address in this cosmic spiral, and many other fascinating facts about the Milky Way galaxy. Here are a few to chew on.

  • The Milky Way is estimated to be 800 billion to 13.5 billion years old
  • The diameter of the Milky Way is 100,000 to 200,000 light years, and the spiral disk is 1,000 light years thick
  • The Milky Way consists of approximately 100 billion stars, a few million of which are locked into supermassive black holes
  • Our Solar system is located about 28,000 light years from the center of this galaxy
  • Finally, it takes our sun (and solar system) 200-250 million Earth years to complete one orbit of the Milky Way galaxy!