How many stars are there in the sky? It's one of the first questions I recall asking as a kid. On that warm spring evening I tried to count them all and had my first encounter with the infinite. That night, beside the lake in the Oregon Cascades, my mind's eye fell upward into a star-filled cosmos vaster than anything I had ever known. At that moment, I realized there was so much more to the universe than me, so much more to search out, question, discover, and understand. It is safe to say that my vision of a thousand, million, (billion?) stars that night awoke the future scientist within me.
How many stars are there in the sky? Where I live now in the suburbs of Los Angeles, there are 12 stars, and they are a sight that inspires no one.
This loss of natural night, the artificial glow that blankets the stars and turns the nocturnal sky orange at night, is called light pollution. This week and every year, it silently steals another dozen stars and does it so slowly that no one notices their absence until one night the stars are gone. This week (April 20-26), the International Dark-Sky Association (IDA), astronomy clubs, and a host of U.S. national parks across the country celebrate International Dark Sky Week to raise awareness of what is happening in the sky overhead.
Current estimates are that fewer than 40 percent of U.S. and European populations can still faintly glimpse the Milky Way where they live. Worldwide, roughly 50 percent of the children born this year will never see the Milky Way. A sight that was once familiar to everyone and stimulated the production of art, myth, and science has faded into obscurity.
To better promote the beauty of a naturally starry sky, and the economic benefit of night-sky tourism and preservation, the IDA and National Park Service (NPS) have partnered to create the International Dark-Sky Places program. Over the last decade, the NPS has found that their astronomy night sky programs are more heavily attended than the next two most popular visitor programs combined. Since 2007, 14 parks and regions around the world have earned this designation. This week, two more parks are being formally added to this list: Chaco Culture National Historical Park in western New Mexico and Parashant International Dark Sky Province in southern Utah and northern Arizona. In Chaco Canyon, there are massive ruins left behind by the ancestors of today's Pueblo peoples that show that there have been astronomers in the Southwest for thousands of years. In Parashant, one of the largest undeveloped stretches of country in the continental U.S., the night sky is a sight unlike anywhere else.
It is natural to imagine that light pollution is a phenomenon that solely affects astronomers. But the impact of light pollution is not limited to night sky enthusiasts. Many species around the world are nocturnal. These species have evolved to hunt, feed, breed, and give birth at night. Yet for many locations, particularly in Europe and North America, natural night no longer falls on what appear to be otherwise pristine habitats. Light pollution regularly interferes with the hatching of sea turtles on Florida's Gulf Coast and the migrations of birds over vast distances.
Even we humans are not immune to the health effects of our brightening skies. The International Agency for Cancer Research and American Medical Association now recognize nocturnal lighting as a probable carcinogen based on studies of women working night shifts who show an increased risk of breast cancer. Other research is finding similar results for those with increased levels of light in the sleeping environment, something that more of us will encounter as our cities get brighter.
As the American Medical Association put it in their 2012 Report of the Council on Science and Public Health:
Biological adaptation to the sun has evolved over billions of years. The power to artificially override the natural cycle of light and dark is a recent event and represents a man-made self-experiment on the effects of exposure to increasingly bright light during the night as human societies acquire technology and expand industry.
Light pollution produces a direct economic loss as well. Every photon of light that our streets, homes, and cities shine up into the air to illuminate birds and spacecraft is electricity wasted. This is electricity we pay for in our households and communities. In a recent economic analysis by Terrel Gallaway, an economist at Missouri State University, the annual costs of light pollution in the U.S. alone is at least $7 billion a year and 66 million metric tons of CO2, the equivalent of 9.5 million cars from of the road.
Surprisingly, the solution is simple. Shield the light and those errant photons as they leave the atmosphere at the speed of light. Place a shield on top of any outdoor light so that the bottom of the shield is below the level of the lighting element (called "full cut-off shielding") and all light that used to shine upward is now reflected back to the ground, increasing the amount of useful light that falls there. If you do not need more light on the ground, then fewer lights or lower-wattage lightbulbs can be installed. In addition, if nocturnal activity is the concern (aiding the good activity and detecting the bad), then the addition of motion sensors puts light exactly where it is needed when it is needed. And even if you don't care about the stars, full cut-off shielding insures that your lights don't shine into your neighbor's bedroom at night and theirs won't shine into yours. As a result, we all get a better night sleep.
In addition to shielding, you can reduce the amount of light pollution by avoiding the increasingly bright white LEDs that many manufacturers are now peddling. Their excess blue light is the kind that our atmosphere preferentially scatters (that's why the sky looks blue) and is also the kind that appears to have the greatest health effect on our bodies.
Consider the magnitude of what we are losing: For all of human history, ever since the first primates who would one day call themselves human climbed down out of the trees and set foot on the African savanna, the stars overhead were a nightly occurrence. The patterns and motions of these stars gave us myths, morality tales, art, religion, and science. They measured the passage of time and allowed us to plant and harvest and predict the coming of the rains, the heat, and the cold. On land they guided our feet, and at sea they guided our ships. They were the catalyst for the scientific method, which has subsequently prolonged life, harnessed the atom, and sent our spacecraft on their way to the stars. The stars we see at night link us to our past and hold the key to our survival in the future. Modern science has revealed that the atoms that compose everything we can see and touch, our entire world and our very bodies, were created in the hearts of stars. As the late astronomer Carl Sagan once said, "We are made of starstuff." Without stars' presence overhead, our universe shrinks to the boundaries of our own tiny world and its glowing atmosphere, and together we are diminished.