Light Pollution Sources - Night Skies (U.S. National Park Service) (2024)
The primary cause of light pollution is outdoor lights that emit light upwards or sideways. Any light that escapes upward, except where a tree or building may be blocking it, will scatter throughout the atmosphere and brighten the night sky, thereby diminishing the view of it. Air pollution particles will also increase the scattering of light at night, just as it impacts visibility in the daytime.
Light fixtures that direct all light downward greatly reduce the amount of light pollution. These are referred to as shielded lights, or the engineering term full cut-off. Some light does reflect off the ground and scatter through the sky, but this has a smaller effect than light that shines directly upward. Light pollution can be further reduced by utilizing a less powerful lamp or bulb. These modern improvements in lighting not only greatly improve the quality of the night sky, but also have other benefits. These include better visibility, improved safety, less energy use, and better aesthetics.
Recent research shows that light that emitted just above the horizontal (slightly upwards) is the most likely to cause light pollution (Luginbuhl, Walker &Wainscoat, 2009). Such light that grazes across Earth's surface is several times more damaging than light that is emitted straight upward. This underscores the importance of using well-designed light fixtures with a full cut-off design.
Outdoor lighting consumes about three to five percent of electrical demand in developed countries. Depending on how light pollution is defined and the local lighting practices, the fraction of outdoor lighting that contributes to light pollution can range from 20 to over 50 percent. Thus, minimizing light pollution also achieves meaningful energy savings on a national scale and provides an economic incentive to upgrade or replace outdoor lighting with more sustainable solutions.
In some instances, even a single light can be disruptive to the natural lightscape. While one light may not affect the entire night sky, the bright point source of light can annoy neighbors (a problem called light trespass), reduce perceptions of solitude and naturalness, confuse nocturnal animals, migrating birds, and insects and spoil cultural landscapes. Even a candle seen from a mile away is brighter than each of the stars in the Big Dipper, so very small amounts of stray light can impact natural lightscapes.
References
Luginbuhl, L., Walker C., and Wainscoat, R. 2009, Lighting and Astronomy, Physics Today, Vol 62:12.
There are natural sources of skyglow, such as the aurorae (northern lights);the greenish airglow (a faint glow from the upper atmosphere present most nights);scattering of the light of the moon, planets, and stars;and the Zodical Light (a band of light along the Zodiac that is part of our solar system).
Due to its incredibly remote location in the far southwest corner of the large state of Texas, Big Bend National Park has some of the darkest skies in the whole USA. In fact, it has the lowest levels of light pollution of any other national park unit in the lower 48 states (there are over 400 of them).
Of the vast amount of certified International Dark Sky Parks and Communities that are part of a catalog of the finest dark skies in the world, the highest concentration are in Utah. Explore the statewide locations and make plans for experiencing natural wonders after the sun sets.
It is most severe in highly industrialized, densely populated areas of North America, Europe, and Asia and in major cities in the Middle East and North Africa like Tehran and Cairo, but even relatively small amounts of light can be noticed and create problems.
Many of America's 63 national parks are dark sky areas, but only 12 are certified by the IDA. These include Grand Canyon, Mesa Verde, Joshua Tree, Death Valley, and Big Bend National Parks.
Many national parks offer night sky programs, from telescope astronomy events to full moon walks with rangers. Click on the collapsible panel below to see a partial list of parks that offer night sky programs.
Boasting some of the darkest nights in Southern California, Joshua Tree National Park, an International Dark Sky Park by the International Dark-Sky Association (IDA), offers many visitors the chance to admire the Milky Way for the first time in their lives.
Virtually free of any light pollution from populated areas, Goblin Valley State Park offers unparalleled views of the Milky Way. A variety of ranger-led events, including moonlit hikes and telescope tours, are conducted every month in order to aid in your enjoyment of this unique resource.
Introduction: My name is Corie Satterfield, I am a fancy, perfect, spotless, quaint, fantastic, funny, lucky person who loves writing and wants to share my knowledge and understanding with you.
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