The sky is in the sun

What is the Milky Way?

In earlier times, the sight of the Milky Way was familiar to everyone: as a shimmering ribbon it stretches across the night sky. Today even bright stars are drowning in the sea of ​​lights in cities. To see the faint glow of the Milky Way, we have to go to a dark place away from the city lights. Then, however, the milky band is an unforgettable sight. But what is the Milky Way?

A 360 degree panorama of the Milky Way

When Galileo Galilei pointed the telescope he had just invented at the sky in 1609, he realized that the Milky Way consists of countless faintly shining stars. The German-British astronomer Wilhelm Herschel concluded in 1785 based on star counts that the Milky Way must be a lens-shaped collection of stars, which also includes the sun and all other stars visible in the sky.

The first realistic estimate of the size of the Milky Way was made in 1919 by the American Harlow Shapley by studying the distribution of globular clusters. He was also able to show that the sun is not - as previously assumed - in the center, but rather in the outer area of ​​the Milky Way. When Shapley's colleague Edwin Hubble showed in the 1920s that the so-called “nebulae” are actually star systems far outside the Milky Way, it was clear that the Milky Way is not a “world island” in otherwise empty space, but just one of countless many Star systems. The technical terms "galaxy" for our Milky Way and "galaxy" for other star systems are derived from the ancient Greek word "galaxias", where "gala" means "milk".

Milky Way from above

Today we know that the Milky Way is a disk-shaped bar spiral galaxy about 100,000 light years in size, containing 100 to 300 billion stars. Our solar system is located about 25,000 light years from the center of the Milky Way on the edge of a spiral arm. Seen from Earth, the center of the Milky Way lies in the constellation Sagittarius (Sagittarius) and is hidden behind dark gas clouds. Observations in the radio and X-ray range show that there is a black hole there with about four million times the mass of the sun. The disc-shaped Milky Way is embedded in a spherical halo made up of globular clusters about 165,000 light years in size. The total mass of the galaxy is now estimated to be 1.0 to 1.9 trillion solar masses, of which about 80 percent can be attributed to the mysterious dark matter.

Since we ourselves are within the disk of the Milky Way, we see most of the stars within a band in the sky - in the Milky Way. But all stars that are outside the Milky Way band in the sky also belong to the Milky Way star system. The term “Milky Way” is used today to describe both the shimmering ribbon in the night sky and the star system to which our solar system belongs.