The Milky Way, the galaxy to which the Earth belongs, appears in the sky as an irregularly shaped band, - with some parts brighter than others - that stretches from horizon to horizon.

Toward the south, the Milky Way appears to be split in two by a dark streak known as the Great Rift, a series of dust clouds located about 300 light-years on Earth.

The ancient Greeks believed that the Milky Way was a road leading to the home of the gods.


In 1609, Galileo used a telescope to look at the Milky Way. He found that the Milky Way contained millions of stars that were too faint to be seen individually with the unaided eye.


Sir William Herschel, a British astronomer, was the first to try to discover the shape of our galaxy.

Herschel counted the number of stars he could see with his telescope in different parts of the sky.

He found that that the number of stars grew larger as the band of the Milky Way was approached.

From this observation, he concluded that the stars were arranged in a great system shaped like a watch.

The Milky Way, as we see it in the sky, is the view that we get of this system from our position inside it.

When we look at the Milky Way, we see so great a concentration of stars because we are looking into the depths of the galaxy. It is as though we are looking along the hands of the watch.

When we look away from the Milky Way, we see so few stars because we are looking out through the face of the watch.

Herschel thought that the Earth's Sun was situated near the center of the galaxy.


In 1916, the American astronomer Harlow Shapley began studying the structure of the Milky Way.

He showed that our Sun was far from the center of the galaxy.

Structure and Size of the Milky Way

Today, we know that the Milky Way consists of a core region surrounded by a disk of gas, dust and stars that forms four spirals.

Our galaxy is about 100,000 light years in diameter and 1,000 light years thick, on average. It contains between 200 and 400 stars.

Astronomers believe that most of the Milky Way's mass comes from dark matter.

Dark matter is a type of matter that does not emit radiation, and therefore cannot be detected by instruments, but whose existence in the Universe explains various gravitational phenomena.

The center of the Milky Way is in the great star clouds in the direction of the constellation of Sagittarius.

There is an extremely large black hole at the center of the galaxy.

The Milky Way rotates about its center. The existence of Dark Matter helps to explain the galaxy's perceived rate of rotation

The Earth's Solar System is located in one of the spiral arms toward the outer edge of the galaxy. Our Sun is estimated to be between 24,000 and 28,000 light years from the center of the Milky Way.