The Milky Way

On a clear, moonless night away from the city lights, you can see a pale white band stretching across the sky. This hazy band of light is our own inside view of the city of stars that form the galaxy we are part of, the Milky Way Galaxy.

There are many myths involving the formation of the Milky Way, but the best known is probably the Greek myth of Hercules. In Greek mythology, Hercules was the son of Zeus and a mortal woman. It was said that when Zeus’ wife, while suckling Hercules, found out that his mother was a mortal woman, she pulled her breast away and her milk flowed among the stars.

But what is the Milky Way really?It is a spiral shaped galaxy, a vast collection of stars, gas and dust of which the solar system with our Sun and its system of planets, is a part. We are located about halfway

from the centre, on the edge of a spiral arm called the Orion-arm. The band of light we see is the light of millions of stars that lie in the disc of the galaxy and often are too far away to be seen as separate stars with the naked eye. Most of the visible mass consists of stellar material like gas, stars, dust and planets, but about 90 percent of its total mass is made up of invisible “dark matter”, which remains a mystery still to be explained.

The geography of the Milky WayAt the very centre of the Milky Way lays a massive black hole. This core, or nucleus, of the galaxy is surrounded by a bulge of stars that grow denser closer to the centre. This forms an ellipsoid of about 15,000 by 6,000 light years, the longest dimension lying along the plane of the Milky Way. Around this, young stars form a spiral pattern. The Milky Way is about 100,000 light years in diameter and about 2,000 light years thick. The spiral arms are named after the constellation that they are most prominent in. The brightest arm is that in Sagittarius, while we are located in the Orion arm.

The closer an object is to the centre, the faster it will move. The Sun travels around the galactic centre at about 800,000 kilometres (500,000 miles) per hour, taking about 225 million years to complete one orbit. Our Milky Way is quite a large galaxy and part of what is called “the local group” of galaxies. This local group also contains the Magelhanic Clouds and the Andromeda galaxy, which are, despite the enormous distances, our closest neighbours.

From Balule I wish you clear skies and happy stargazing.
Miriam