The Milky Way

The galaxy that is home to the Earth itself is known as the Milky Way, an immense banded spiral in space that, when observed from afar, appears to be a spinning blade made from misty tendrils.

A Matter of Scale

The Milky Way is thought to be comprised of 200 billion to as many as 400 billion stars, of which the Sun is but one. The main part, or disk, of the galaxy is somewhere between 800k to 100k light years in diameter and 250k to 300k in circumference. Outside of the Galactic core the Milky Way is about 2,500 light years from “top to bottom”. To get a good grasp on where exactly the solar system (not just Earth) fits in the Milky Way, imagine that the entire galaxy was shrunk down to a bit smaller than the size of London, the solar system would be about 2 millimetres wide.

As huge as the Milky Way is, it is but a small part of the Universe at large. It is part of a local gang of galaxies inside what is known as the Virgo Supercluster, which in turn houses around 100 galaxies of various shapes and sizes.

A Look at the Milky Way

It has been estimated, based on research done in 2004 that the Milky Way is between 13 billion and 14 billion years old. The centre of the galaxy is called the “galactic disk” and it is estimated that our Sun is between 25,000 light years to 35,000 light years from the centre of the disk. What lies at the centre of the disk is an object of very great density, and is thought to be a super massive black hole. In fact, most galaxies are thought to have a super massive black hole at their centre. The object at the centre of the Milky Way has been named Sagittarius A.

There are thought to be four massive spiral arms that comprise the Milky Way: Perseus Arm, Cygnus Arm, Scutum Arm and Sagittarius Arm—none of which house our solar system. The sun is located in a spur, or smaller arm, called the Orion Arm.

Outside of these arms is a ring called the Outer Ring or Monocerous Ring, and is thought to be captured stars and gasses from other galaxies, pulled in by the collective mass and gravity of the Milky Way.

The Milky Way Habitable Zone

Just as a planet must be within the habitable zone of a star to support life, so must an entire solar system lie within such a zone, called the “galactic habitable zone.” To be in this zone means the solar system has to be close enough to the galactic centre in order for enough heavy elements to exist in order to build rocky planets, not to mention the presence of certain heavy elements such as iron and iodine, necessary components for life itself to form.

Final Thoughts

The Milky Way is so immense, lifetimes could be spent exploring it, yet it is over all a very small part of the universe. Thanks to continuous advancement in astronomical science, mankind’s ability to explore well beyond its reach grows more and more each year.