Seven Words That Can Change the World

The Milky Way galaxy is huge. It contains about 300 billion stars. The nearest to us of the 300 billion is a star by the name of Proxima Centauri. It is one of a three-star system that also includes Alpha and Beta Centauri, which tumble over each other while Proxima Centauri orbits them. To reach Proxima Centauri from our solar system, traveling at the speed of light, 186,000 miles per second (at that speed, we could fly around Earth seven times in one second!), requires four years and three months. To make that same trip at today’s space-shuttle speed would take 155,000 years! That’s to reach the nearest star of approximately 300 billion in our galaxy.

Just how big is this galaxy? The Milky Way is 100,000 light-years wide. A light-year is the distance covered in a year traveling at the speed of light, 186,000 miles per second: 5,880 billion miles. Multiply that times 100,000 and you have the distance across our galaxy. There is another way, perhaps a little more comprehensible, to visualize something 100,000 light-years wide. If we started at one end of our galaxy and traveled across it at 186,000 miles a second (the speed of light) for every second of every minute of every hour of every day of every year for 100,000 years, we would reach the other end. It’s large. The word “incomprehensible” comes to mind. As recently as the 1920s, we thought the Milky Way galaxy was the entire universe. This was an error equivalent to thinking the earth was flat.

As large as our galaxy is, we now know it is only one of 100 billion galaxies in the observable universe. Why do we say the “observable universe?” We exist on one of the spiral arms of the Milky Way galaxy. The gas, dust, and other stars (approximately 300 billion) in our galaxy block our vision, preventing us from observing the rest of the universe. Even though we can actually observe 100 billion galaxies, we estimate that there exists a trillion galaxies in the known universe. Scientists are now pondering the probability that there are many more universes. The nearest large galaxy to us is Andromeda, which contains about 400 billion stars. To reach Andromeda from the Milky Way, we would have to travel at the speed of light, 186,000 miles per second, for 2,200,000 years.

Galaxies are organized into clusters and super clusters. The Milky Way, Andromeda, and more than thirty other galaxies exist in a cluster by the name of the Local Group. The Local Group is 10 million light-years wide and sits on the edge of a super cluster by the name of Virgo. Virgo is hundreds of millions of light-years wide. To cross it requires hundreds of millions of years of travel at 186,000 miles per second. It contains thousands of galaxies. However, in cosmic terms, thousands of galaxies is not a big deal. Remember, there are an estimated trillion galaxies in the known universe. This super cluster, Virgo, with all its galaxies, is being drawn at a speed in excess of a million miles an hour toward some unfathomable mass that some cosmologists refer to as The Great Attractor.

Let’s review all of this briefly. In general terms, our universe consists of clusters and super clusters of galaxies. These galaxies contain billions of stars like our sun. Planets orbit some of these stars. Moons orbit some of these planets. We exist on a planet orbited by a moon. Our planet and its moon orbits a star, the sun, at 65,000 miles per hour. The sun, along with the rest of our solar system, orbits the Milky Way galaxy at 600,000 miles per hour. The Milky Way galaxy, with all its stars, planets, and moons, travels among other galaxies at speeds in excess of a million miles an hour. This is the incredible system in which we exist and of which our tiny planet is an infinitesimally small part, a mere speck on the blueprint of existence.

Filed under: cosmology