Everyone knows that our planet Earth is part of the clearly defined Solar System. However if we take a step back it is clear that our planet is part of a much bigger and more complex structure. As early as the prehistoric man, humans have been intrigued by the mysterious milky strip that lines the night sky. Only with the birth of modern astronomy have scientists been able to analyse the millions of stars which are lie trillions of miles from Earth.
The term “Milky Way” comes from Classical Antiquity to describe the band of light in the nights sky and has become the name of our galaxy ever since. Part of a collection of 54 galaxies, the Milky Way is a spiral barred galaxy like many other known galaxies. Measuring 100 000 to 180 000 light years in diameter and 1000 light years thick, it is believed that the Milky Way consists of between 100 to 400 billion stars. However as our galaxy is constantly evolving as new stars are born or old ones die, it is very difficult to estimate exactly how many stars make up our galaxy.
The Milky Way has a Galactic Centre and a Galactic Disk which consists of four spiral arms that are surrounded by a halo of old stars and globular clusters. Approximately 10,000 light-years away, the Galactic Centre, also known as “bulge,” is a dense concentration of old stars. This region is also the Milky Way’s rotational centre. An intense radio source called Sagittarius A is found at the centre our galaxy. Due to the apparent gravitational influence of this radio source, it is probably an enormous black hole. It’s mass is believed to be between 4.1 and 4.5 million solar masses.
Around the Galactic Centre there are four spiral arms; two big arms and two smaller ones. However, as yet, there is no consensus on the exact structure or extent of these arms. These arms tend to contain a higher density of interstellar gas and dust as well as a higher concentration of star formation than the rest of the galaxy. Our solar system is found on the “Orion” arm which is mainly composed of red (older) stars and lies about 28 000 light-years away from the Galactic Centre. It is believed that the “Orion” arm takes around 250 million years to rotate around the galaxy. Our Solar System could have carried out between 20 and 21 galactic revolutions since its formation about 4.5 billion years ago.
Although you can’t feel it, our planet orbits the Sun at a speed of about 100,000 km / h. However this nothing in comparison to the fact that our Galaxy moves through space at the phenomenal speed of 2 million km / h. (The equivalent to about 630 km per second). At the same time our galaxy is pulled by a supercluster located about 600 light-years away and is pushed by a vast, sparsely packed galactic region.