Of all the sights visible in the nighttime sky, none is more awe-inspiring than the view of the Milky Way galaxy.
Telescopes won’t help you here. Our galaxy spans the entire sky like the backbone of God.
However, to see it, you must find an observing location away from the cities where the sky is clear and unfettered by the blinding glow of streetlights. I am always surprised that we can still see it so well from Perkins. Local development may soon spoil the view, but the cooperation of local developers has kept the glow from outside lighting down sufficiently that our galaxy is still visible. Such may not always be the case.
Still, the best view is from deep, deep in rural Ohio. Simply look up. Just after dark, the Milky Way will stretch brightly from the southwestern to the northeastern horizon in a broad band. Once your eyes adapt to the darkness, you will see dark rifts and complex undulations, an unforgettable sight.
You see the galaxy as a band because of where you live in it. The Milky Way is actually shaped like a child’s pinwheel, a flattened disk of 300 billion stars with a bulged center and spiral arms radiating from the central hub. You live out on the edge of the galaxy — about two-thirds of the way out from the central hub in one of the spiral arms.
If you were a flea on the edge of a pinwheel, you would see the pinwheel with a bulge at its center and a long bar with elongated fingers that suggest its spiral shape.
Look low in the southwest for the teapot-shaped “summer” constellation Sagittarius, still hanging in there. Running through and around it is the galaxy’s central bulge. High in the southwest is the cross-shaped constellation Cygnus. Follow the stream of light to the southwest and you are looking into one of our galaxy’s spiral arms.
The best close-up view of the Milky Way can be had with a simple pair of binoculars. For thousand of years, humans had speculated about the streak of light you are seeing. With a telescope smaller than your binoculars, Galileo ended their confusion once and for all. The streak resolved into countless stars, and our view of the universe changed forever.
The Milky Way is, of course, only one of hundreds of billions of galaxies. How they got the way they are is one of astronomy’s greatest mysteries.
According to recent theories, the universe began around 12 billion years ago in a stupendous explosion called the Big Bang. Eventually, the pristine elements hydrogen and helium formed to make up most of the cosmos. (They still dominate the universe today.) For reasons still unknown, the primordial gases clumped up into spinning clouds. One of them eventually became the Milky Way.
At first, our galaxy was spherical, a ball consisting of 75 percent hydrogen and 25 percent helium. The ball collapsed into a still-spinning disk, and the disk developed spiral arms because the outer part was moving more slowly than the inner hub. The outer parts of the arms trailed behind the inner parts.
Some parts of the gas were denser than others. The gaseous stuff of the Milky Way began to concentrate into clouds.
In those clouds, spinning balls of mostly hydrogen formed. When the balls got massive enough, their internal pressures caused them to explode with the power of hydrogen bombs. Stars had been born.
Some of the original stars burned rapidly and thus formed heavier elements like carbon, calcium and iron. Those stars quickly died in enormous explosions called supernovas. They spewed forth their star stuff, enriching the existing clouds with the heavier elements. The shock waves from the explosions further compressed and condensed the gas clouds, encouraging further star births.
Our sun was formed in that second generation of stars. Its birth was similar to the galaxy’s but on a much smaller scale. A swirling disk of gas had been seeded with the heavier elements that form solid planets. The central hub of the swirl became the sun. The outer parts of the swirl condensed to make planets like
Earth is a place for us to live, to be sure. But it is also a place to stand. From our tiny vantage, we can look outward into space and backward into time at the glorious Milky Way, our larger and more magnificent home.
Tom Burns is director of Ohio Wesleyan University’s Perkins Observatory in Delaware. firstname.lastname@example.org