Let’s continue trying to visualize the size and scale of our universe with a discussion about our Milky Way galaxy. Galaxies are large collections of stars, on average about 100 billion stars, that come in different shapes and compositions. There are elliptical galaxies (which have basic shapes of spheres or eggs), spiral and barred spiral galaxies (which have a basic shape of a disc), and peculiar galaxies (which have, as their name suggests, irregular shapes). The galaxy our Sun is part of is a barred spiral galaxy, which means that as you look down on it from above, it sort of looks like a pinwheel with a short, straight bar through the center, and as you look at it from the side it looks thin like a disc with a bulge at the center. Our Sun is in one of the pinwheel arms called the Orion Spur and is located about halfway from the edge of the galaxy and its center. Our galaxy rotates and it take about 200 million years for the Sun to orbit the galactic center. To try to imagine the size and scale of the Milky Way, let’s begin with imaging our Sun as a penny. If the Sun was that size, the nearest star, Alpha Centauri, would be 350 miles away! So on this scale, the Milky Way is about 8 million miles across, or about 30 times the distance between the Earth and the Moon!
Let’s try a different scale: if the Sun was a grain of sand, the Earth would be a microscope speck one inch away, Pluto would be 40 inches away, Alpha Centauri would be about 4 miles away, and the diameter of the Milky Way would be still be an incredibly large 100,000 miles!
Next week we’ll try to imagine the vastness of the universe!
Follow your curiosity to the Fred G. Dale Planetarium at Wayne State College.