A place to stand

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.

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. tlburns@owu.edu

Posted by Tom Burns on Oct 23 2011. You can follow any responses to this entry through the RSS Feed. Comments can be made below.