The Milky Way as seen from Earth

Image: ESO/S.Brunier (CC BY-SA 4.0)

The Milky Way

An ancient Greek myth tells how Hera, the wife of Zeus, nursed the infant Heracles. Some of her milk splashed across the sky. This is how people explained the bright band in the night sky. Today we know it is formed by the light of countless stars in our galaxy. Even so, we still call it the Milky Way.


The Milky Way contains an estimated 100 to 400 billion stars. Our Sun is one of them. Many stars are too dim to see or are hidden behind clouds of dust. That’s why we can only estimate their number. The Milky Way resembles a flat disc with a bulge in the middle and several spiral arms. This disc of stars is about 100,000 light-years across. So light takes about 100,000 years to travel across it.


The Milky Way began to form around 13 billion years ago. New stars are still forming today, while others are reaching the end of their lives. Our Sun is about 4.6 billion years old. It takes around 230 million years to orbit the center of the Milky Way once. A huge black hole lies there.


Our nearest neighbouring stars are called Alpha Centauri A, Alpha Centauri B and Proxima Centauri. They are a little over four light-years away. Planets have already been discovered orbiting Proxima Centauri.


The next large spiral galaxy is the Andromeda Galaxy. It is about 2.5 million light-years away. That means we see it as it looked 2.5 million years ago. Its stellar disk is about twice as wide as the Milky Way’s. Both galaxies are moving toward each other. Whether—and when—they will collide is still uncertain.

Study sentences

  1. A Greek myth tells how the milk of the goddess __________ splashed across the sky.
  2. The bright band in the night sky is formed by the light of countless __________.
  3. We call our galaxy __________.
  4. The Milky Way is estimated to contain __________ million stars.
  5. We cannot see many stars because they are too dim or are obscured by __________.
  6. The Milky Way's disk is approximately __________ light-years wide.
  7. Our sun is about __________ billion years old.
  8. It takes the Sun about 230 million years to orbit the __________ of the Milky Way once.
  9. At the centre of the Milky Way is a huge __________.
  10. The next large spiral galaxy is called __________ and is about 2.5 million light-years away.
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