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Mercury, September/October 1997 Table of Contents

James C. White II
Middle Tennessee State University

Making our cities bright and safe can render the Milky Way invisible. But with just a little effort, perhaps a short trip to the countryside, you can recapture the sight of our Galactic metropolis.

I remember the day the Milky Way disappeared. I was 8 years old and had spent a couple of hours the night before in the pasture beside our barn, just lying there under the sticky warmth of a late summer evening in southern Tennessee. I had seen illustrations of what our galaxy was supposed to look like, but that north-south stretch of diffuse starlight looked more like, well, spilled milk.

The Milky Way is an average-sized spiral galaxy, one of about 100 billion islands of stars in the universe. And what we know about it has been very difficult to come by. Imagine that you've lived in your house since birth and never left it, not even to buy an ice-cream sandwich. The telephone rings and the caller asks you to describe what your house looks like. Easy. "It's got big, fluffy chairs and lots of small porcelain animals and..." But the caller interrupts and asks what your house looks like on the outside. What do you say? If you're quick-witted, you use the few clues you have around you to construct a description of your home: the straight, parallel lines; the right angles; the shadow your house casts; the appearance of houses that are visible out your window.

This is how astronomers have gone about discovering the nature of our home galaxy. In the 18th century, an Englishman and a German began the process with simple observations. Thomas Wright in 1750 and Immanuel Kant in 1755 suggested that the band of light we see is a flattened disc of stars. The disc looks to us like a band because we are inside it. Kant held to this audacious yet refreshingly correct image, but Wright eventually got a little strange and started saying the Milky Way was actually lava.

Regardless, the image was cast, and since then humans have whittled and etched and polished it into the one we have today. An enormous pinwheel of a few hundred billion stars is our neighborhood. It has several parts. Looking like two dinner plates pressed together, the visible disc is 100,000 light-years across and a thousand light-years thick. Toward the middle there's a swelling called the central bulge, and outside the disc there's an enormous sphere called, somewhat misleadingly, the halo. The halo roughly outlines the womb our galaxy sprang from. These days, the disc is where the action is: spiral arms where the night life is happening, star clusters where the fashionable stars congregate, molecular clouds where stars are born. And the Sun and you and me.

On that day 27 years ago, two outdoor security lights were installed near my house. One was near the barn, the other near the house. I understood the need for safety, but my Milky Way was gone. I had to wander to back pastures for darkness and the peaceful thrill of seeing that canopy overhead. But it wasn't the same.

Observing Guidelines

Being a good observer requires dedication, creativity, a love of hot chocolate (OK, maybe not, but it helps, I bet), and the ability to discriminate. Stars are dots to the naked eyes, bright dots through binoculars, brighter dots through a telescope -- frankly, they can get a bit boring, unless you like dots. But nebulae and galaxies are glorious extraterrestrial works of art. They are intricate, extended regions of subtle color variations. These variations communicate volumes of information to professional astronomers about the distribution of stars and the gassy material among them.

This month's project has two goals: to practice our ability at observing subtlety in nature, and to appreciate the visual extent of the Milky Way. Your observations will require paper, pencils, sky charts, and most important, a clear, dark, moonless sky. Because the variations can be quite small, dark skies are crucial to your observations.

Use tracing paper to make a copy of the brightest stars on your star chart. These will frame your observations and establish constellation regions in your drawings. Tape your paper to a tray or something similar, and plan on just sitting and staring at the sky for a while. Record the time and date, and describe the skies and weather. Note from one session to the next how humidity and haze affect your view. Use your pencil to shade the areas on the paper which match what you see in the sky. Be gentle here, and use your fingers to blend the pencil markings.

What should you see? This really depends on your location and sky conditions, but generally you'll see the Milky Way stretched as a band between the northeastern and southwestern horizons. Observers in the Southern Hemisphere will see the Milky Way holding Crux and Norma and Scorpius, while Northern observers will see Perseus and Cassiopeia in the midst of the band's faint glow. Observers in both hemispheres will notice a thickening in the Milky Way toward Sagittarius. No surprise here--Sagittarius lies in the direction of the center of the Galaxy, and the constellation's famous teapot appears to be pouring a spot of tea right toward the center. Amazing, huh?

Incorporate your observations into a document with the following information: name of the project (such as, "Observing the Milky Way"), your name or the name of your group, details of the observing location, date and time, sky conditions, mailing address, telephone number, and email address, if available. We welcome reports from observers of all ages in all countries.

Please submit your completed report by Nov. 30, 1997, by regular mail to Jay White, Attn: Guest Observers, Department of Physics and Astronomy, Middle Tennessee State University, Murfreesboro, Tenn. 37132. The selection committee will evaluate the reports and choose the Guest Observer for a future issue.

JAMES C. WHITE II is an astronomy professor at Middle Tennessee State University. Even he, in bucolic Murfreesboro, is forced out of town and into the dark, honeysuckled hills of Tennessee for a better view of the Milky Way. His email address is jwhite@physics.mtsu.edu.