How good is the night sky over your house? How well can you see the stars? How many stars can you see from your house? This month, a nationwide program and a worldwide effort attempt to find these answers and show you ways to improve your view of the No. 1 natural wonder of the universe: the beauty of the night sky.
Many factors determine how well you can see the night sky. Natural weather patterns have an obvious effect. But even when clouds are not seen, high haze, which may well be invisible to you, can obscure many stars. Humidity causes air to scatter light, reducing the contrast between the "black” sky and the stars, making fainter stars harder to see and stars close together difficult to distinguish. What you might see as three stars on a clear, dark night may look like only one with high levels of humidity in the air.
But by far the biggest thief of the night sky is light pollution. Light pollution won't cause physical or mental health problems. It won't give you cancer, but it is a cancer on the beauty of the night sky. It robs us of a natural treasure.
The International Dark-Sky Association ( www.darksky.org
) defines light pollution as "any adverse effect of manmade light. It is often used to denote urban sky glow.” The association describes several types of light pollution, including glare, light trespass and energy waste. All forms of light pollution deal with light going to places where it is not needed or wanted. Some forms of light pollution, while intended to make you safer at night, actually do more harm than good.
From an astronomical point of view, all forms of light pollution add to sky glow, light that shines up above the horizon into the sky. That light does nobody any good: It won't increase your safety; it won't allow you to better see oncoming traffic or deter a burglary of your house or business at night. But it does take away the beauty of the night sky. When is the last time you actually saw the Milky Way?
The first step is evaluating the problem. The international program Globe at Night sets out to do that. For several years, the organization has collected and analyzed observing reports from around the world. People like you go out during the Globe at Night evaluation period and count the stars visible from your house in a particular part of the sky. During the 2007 event, the program received 8,491 reports from 60 countries. This data, collected during several years, allows scientists to evaluate the state of the sky around the world.
The 2008 Globe at Night event is under way. It started a week ago, but you still have time to participate. The observation window extends through Saturday. For details, go online to www.globe.gov/GaN
. The Web site contains all the information you need to be involved. Students and families are encouraged to participate in a global campaign to observe and record the visible stars as a means of measuring light pollution in a given location. By locating and observing the constellation Orion in the night sky, people from around the world will learn how the lights in their community contribute to light pollution.
Organize your own "star party” with friends and family and count the stars you can see in Orion. E-mail them to the program, and you will have participated in a major worldwide scientific study. Your contributions to the online database will document the visible nighttime sky.