milky way from earth

The Milky Way, from the bright star Sirius in the upper right corner all the way down to Eta Carina, the red nebula visible on the horizon, as seen from the Florida Keys. See more pictures of the Milky Way.

Tony Hallas/Science Fiction/Getty Images

A look at the night sky at any time of year will reveal a faint band of light stretching across the sky, either through the middle or near the horizon. The ancient Greeks saw this band o­f light and called it "galaxies kuklos," for "milk circle." The Romans called it the "Milky Way." In 1610, Galileo used the first telescopes and determined that the light of the Milky Way comes from billions of dim stars that surround us.

For centuries, astronomers asked many basic questions about the Milky Way. What is it? What is it made of? What is it shaped like? These questions were difficult to answer for several reasons.

  1. We live inside the Milky Way. It's like living inside a gigantic box and asking, what is the box shaped like? What is it made of? How do you know?
  2. Early astronomers were limited by technology. The early telescopes weren't very large, didn't have much range and couldn't magnify great distances or resolve them.
  3. Early telescopes could detect only visible light. The Milky Way contains a lot of dust that obstructed their views. In some directions, looking at the Milky Way is like looking through a dust storm.

The 20th century brought great advancements in telescope technology. Large optical, radio, infrared, and X-ray telescopes (both ground-based and orbiting space telescopes) allowed astronomers to peer through the vast quantities of dust and far into space. With these tools, they could piece together what the Milky Way actually looks like.

What they discovered was amazing:

  • The Milky Way is actually a galaxy -- a large system of stars, gas (mostly hydrogen), dust and dark matter that orbits a common center and is bound together by gravity.
  • Our galaxy is spiral-shaped.
  • Contrary to popular belief, our solar system is not at the center of the galaxy.
  • The Milky Way is but one of billions of galaxies in the universe.

Come follow us on a journey of discovery as we explore the Milky Way. We'll examine how astronomers figured out its shape, size and structure. We'll look at how the stars within it move and how the Milky Way compares to other galaxies.