NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 18 3.2 Exposure Mechanisms: How Artificial Light at Night Affects Humans Often, light pollution is thought of as affecting the visibility of the night sky and particularly the visibility of celestial objects, and many may consider light pollution to be almost exclusively an aesthetic effect (e.g., interference with the ability to enjoy the stars and the Milky Way). In reality, light pollution affects a wide range of human values and can cause health issues for people, animals, and ecological resources (effects on ecological resources are discussed in Sections 3.4 and 3.5). The exposure mechanisms discussed in this section include: • Increase in brightness of the night sky. • Effects on visibility of objects in dark or near-dark conditions. • Too little light or too much light. • Light trespassing where it is not wanted. Artificial light at night may interact with other annoyances that affect humans (e.g., disruption of sleep from artificial light may be exacerbated by noise).There may also be synergistic effects between the various types of light pollution, such as glare and light clutter combining to increase nuisance effects. 3.2.1 Increase in Brightness of the Night Sky Skyglow makes it difficult to see the stars, planets, Milky Way, and other celestial objects. Human activities that rely on or are enhanced by clear visibility are affected by skyglow. This can include stargazing; enjoyment of naturally dark environments for various nighttime recreational activities; amateur and professional astronomy; and cultural, religious, and spiritual-based activities. In addition, the inability to see celestial objects interferes with understanding and enjoyment of certain cultural and historic sites that have an association with the night sky. Photographs of the constellation Orion show the effects of skyglow on the visibility of stars. The photo on the left is from the dark sky friendly BLM-managed Agua Fria National Monument. The photo in the center is from the outskirts of Phoenix, Arizona. The photo on the right was taken from an urban sports field. Skyglow can substantially increase the brightness of the night sky, reducing the visibility of celestial objects.
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