Milky Way is 1 of 2 trillion galaxies
By Amanda Jermyn



Our galaxy, the Milky Way, was formed about 400 million years after The Big Bang, or about 13.6 billion years ago. In Greek mythology it was created from milk spilled by the goddess Hera while nursing Heracles, but we now know it to be a disk-like region of space about 100,000 light years in diameter, comprised of gas, dust and stars gathered together under the influence of gravity. At its center is a supermassive black hole.

The Milky Way is a barred spiral galaxy, with four spiral arms of gas, dust and stars, rotating in space like a giant pinwheel. However, because we live inside the galaxy, on one of the spiral arms about half way from its center, it is impossible for us to view our galaxy’s spiral shape, and even our space telescopes can’t venture beyond the Milky Way to take photos of it as a whole. So how do we know its shape?

One clue comes from observing the Milky Way from a dark place with the naked eye. What we see is a long, narrow band of stars stretching across the night sky. This suggests that we are seeing a flattened disk viewed from the side, with us located near the plane of the disk. If our galaxy were spherical or egg-shaped, we would see stars spread more diffusely across the sky, rather than concentrated in a single band. And if we were farther away from the plane of the disk the Milky Way would glow brighter on one side of the sky than on the other. Furthermore, we can see a slight bulge at the center of the disk. Given that most spiral galaxies have a similar bulge at their center, it seems likely that our own galaxy is spiral too.

Astronomers have also mapped the positions and distances of hundreds of millions of stars in our galaxy. This has helped determine the general shape of the galaxy and allowed us to create a model of it. While you can never view a photo showing the Milky Way as a whole with its spiral shape, you can observe images of similar spiral galaxies.

In addition, when we measure the movements of stars and gas in our galaxy we find that they are characterized by rotational motion rather than random movement. Such rotational motion is another characteristic of spiral galaxies.

Another clue comes from the clouds of ionized hydrogen from the formation of hot, young stars found in the Milky Way’s disk. As similar hydrogen clouds are known markers in the arms of other spiral galaxies, finding them in the Milky Way bolsters the notion that our galaxy is spiral too. We’ve also come to discover that the color and dust content of the Milky Way is similar to that found in other known spiral galaxies.

The Milky Way is home to you, me, about 400 billion stars and 100 billion planets. It resides within a cluster of galaxies called the Local Group, which in turn is part of the Virgo Supercluster. Though our galaxy may seem immense, it is just one of about two trillion galaxies in the observable universe. While we may never be able to see our home galaxy from the outside, its place within the vast universe inspires our dreams and imagination.

While there is no public Stars Club meeting in December, on Friday, January 3rd at 7:30pm, the Stars Club and the Springfield Science Museum will host “Stars over Springfield,” an astronomy adventure for the whole family. Amateur astronomer Jack Megas will give a talk on “The Winter Stars.” A fee of $3 for adults and $2 for children under 18 will be charged.