Because you're taking the time to read this column, I will assume you know that the Milky Way is not only a candy bar.
But have you ever actually seen it?
For an increasing number of people, the answer is "no." More on that in a moment. First, some background.
The Milky Way is the galaxy ― the gravitational grouping of more than 100 billion stars ― to which our sun belongs. It's what's known as a barred spiral galaxy. Most of the stars in it are located in the central, bar-shaped region from which two long, spiral shaped arms protrude.
Our sun is not in the center, but out in one of the arms. In celestial terms, we're out in the sticks. What's more, all the other stars you can see in the night sky are out in the spiral arms with us. The rest of the Milky Way's stars ― and remember, that's most of them ― are in the bar-shaped region of the galactic center, much too far away for us to see them individually with the naked eye.
But we can see them collectively. That big, dense region of stars ― think of it as "the big city" to us folks living out here in the sticks ― is visible as a soft river of light that seems to flow across the night sky. That's why it came to be called the "Milky Way," or the Via Lactea if you lived in ancient Rome. The word galaxy, itself, is derived from the ancient Greek word gala: milk.
As a skygazing object, the "Milky Way" is really the disk shape of our galaxy, as viewed from the edge. That's our vantage point, out here in one of the spiral arms.
Not so milky these days
The trouble is that for people living in densely populated regions like ours, the Milky Way has all but disappeared.
It's not quite completely gone. In a clear sky during a new moon (the "new" moon is the phase when no moon is visible), you can still see it, especially if you stand outside for at least 15 minutes and let your eyes adjust to the dark. It's then that you should be able to perceive a dim ribbon that crosses the whole sky ... and is just a little bit less dark than the sky on either side of it. There you have it: the Milky Way.
Expecting more? Underwhelmed? You should be. Two-hundred fifty years ago Ben Franklin enjoyed a much better view from our region.
Unfortunately, with the lights of Philadelphia to our east, Reading to our west, and thousands of shopping centers, ball fields, and other sources of artificial light in our own towns, we don't give the Milky Way much of a chance to show itself. The Dark Sky Finder illustrates the severity of the problem in the eastern U.S., particularly in the Northeast (the warmer the color, the harder it is to see stars).
Taking back the night
Local governments in some areas have taken steps to combat the problem of "light pollution," as it's known to astronomers. Streetlamps and other outdoor lighting fixtures that are designed to limit the amount of "waste" light that goes into the sky are available. In Tucson, Ariz., where I once lived, lighting fixtures on public property and many large business sites are required to be astronomy-friendly. The Kitt Peak National Observatory, about 50 miles west of Tucson, is a major beneficiary of these codes and has yielded a number of important astronomical discoveries.
Closer to home, Cherry Springs State Park in Potter County, is home to one of the darkest skies east of the Mississippi River and is one of only four official "dark sky preserves" in the United States. For a small park fee (about $4), you can take your own telescope there and set up for the evening. Public stargazing events are also held.
What can you do about light pollution in your own backyard? For starters, you can reduce your own home's light pollution by turning off external lights or even replacing them with fixtures that direct the light at the ground. Such fixtures also save money and energy by requiring less power to illuminate the same amount of ground as typical light fixtures. The International Dark Sky Association maintains a list of outdoor lighting fixtures that have received its seal of approval.
If you're not ready to dive into dark sky preservation with both feet, that's okay. There's still something you can do.
The GLOBE at Night project, sponsored by NASA and the National Science Foundation, among others, is inviting stargazers around the world to help them get a handle on the problem of light pollution between now and April 4.
For the most part, all you have to do is go outside between 8-10 p.m. and look at the stars.
Then you provide the GLOBE at Night website with your latitude and longitude ― use a GPS device or one of the map tools on its website ― and compare your view of the constellation Leo with their magnitude charts. Pick the one that looks most like the Leo you see. (Most people in our area will probably pick something between "Magnitude 2" and "Magnitude 4.") Report your observations, then browse results from other skygazers around the world.
If you happen to be an elementary school teacher or a parent whose child has taken an interest in the night sky, the GLOBE at Night folks have all sorts of materials to help kids become Dark Skies Rangers.
It's not just about pretty stars
Lest anyone think all this handwringing over light fixtures is solely for the benefit of a bunch of telescope-collecting nerds like me, consider that until about 110 years ago, none of the animal species on the planet had ever encountered artificial light.
So, what? Well, humans might be used to living with it, but wildlife is not. Watch this video of migratory birds flapping around in disoriented circles in the "Tribute in Light" periodically turned on at the site of the World Trade Center to commemorate the terrorist attacks of September 11, 2001.
An abundance of artificial light at night confuses birds, nocturnal insects, bats, sea turtles, and any number of other creatures that rely on the sun, moon and stars to know when to be awake, when to reproduce or where to go.
Think of that before you leave your porch light on tonight.