Everyone knows that we live in the Milky Way galaxy, but you are not the only to ever ask ‘why is our galaxy called the Milky Way?’ the name almost makes you wonder if the person who named it was craving a candy bar. So which came first, the galaxy name or the candy? Well, that answer will be at the end of this article, long after the answer to how the galaxy’s name came about.
The Latin name for our galaxy is Via Lactea. It translates literally as Road of Milk and is so called because of the pale band of light formed by stars in the galactic plane as seen from Earth. It appears to be a milky patch of sky that rings the Earth. The name of the person who came up with this reference has been lost to prehistory, but it was in such common use by the time Galileo realized it was an area packed with stars, that any other name could not have been used. It was hundreds of years after Galileo that it was realized we were looking at an edge on view of our own galaxy, one of billions in the universe.
The Milky Way is a a spiral galaxy, but some observations suggest that it could be fully classified as a barred spiral galaxy(a spiral galaxy with a central bar-shaped structure composed of stars). It contains 100-400 billion stars and an estimated 50 billion planets. It is believed that as many as 500 million of those planets could be within the habitable zone of their parent star. Our galaxy is part of the Local Group of galaxies and is one of approximately 200 billion galaxies in the observable universe. Those numbers could grow as out technology improves. Our solar system is located halfway out from the center of the galaxy, on the inner edge of the Orion-Cygnus Arm. The Sun orbits around the center of the galaxy. That orbit lasts one galactic year, which is equivalent to somewhere between 225 and 250 million Earth years.
Now, as promised, which came first; the galactic name or the candy bar. The name of course. The candy was invented in 1923 and no one can remember who named the galaxy. The composer of the name is not important, but the wonders of the galaxy will fascinate us for thousands of years to come.
We’ve also recorded an episode of Astronomy Cast about galaxies. Listen here, Episode 97: Galaxies.