Escape Light Pollution: Distance Needed From Cities

Light pollution is a growing problem for astronomers and stargazers alike. Even in relatively remote locations, light pollution from cities can wash out the night sky. Sources suggest that light pollution maps can be used to find locations with low light pollution, but these are not always accurate. Other factors, such as weather conditions and the direction of the closest light dome, can also impact light pollution levels. Some recommend a distance of at least 5 miles from a town of 100, 20 miles from a population of 1000, and 50 miles from a population of 10,000 to avoid light pollution. However, light pollution can still be evident even at 25 miles away from a city. To truly escape light pollution, one may need to travel to remote locations far from any major cities or towns, such as central and northern Nevada, southwestern New Mexico, northern Arizona, and eastern Oregon.

Light pollution maps

When using light pollution maps, it's important to understand the Bortle scale, which measures the darkness of the night sky. The scale ranges from 1 to 9, with lower numbers indicating darker skies. Bortle 1 skies are almost entirely free of light pollution, with no light domes from nearby cities or villages, and offer the best opportunity to see faint celestial objects.

In practice, finding truly dark skies requires travelling to remote locations far from cities and major highways. In the continental USA, some of the best places to find dark skies are in central and northern Nevada, southwestern New Mexico, northern Arizona, eastern Oregon, and parts of Wyoming. Residents of less populated areas in the western and mid-western states may have a shorter drive to reach suitably dark skies. For example, those living in small towns may only need to drive 15-30 minutes to escape light pollution completely.

However, even in relatively remote locations, light pollution can still be an issue. For instance, certain spots in the San Bernardino Mountains, like Big Bear and Crestline, offer darker skies than nearby cities, but a large light dome from Los Angeles still washes out a significant portion of the sky. Similar issues occur in parts of Joshua Tree National Park and Palomar Mountain, where light pollution from nearby metropolitan areas can ruin the view. Therefore, it's important to use light pollution maps as a guide and be aware that even in areas with low light pollution, some light domes may still be visible on the horizon.

Distance from towns

Light pollution can be a major nuisance, especially for those interested in astronomy. Even at 25 miles (40 km) away from a city, light pollution can still be evident. The glow of Phoenix, Arizona, for instance, is noticeable from Kitt Peak, which is 160 km to the south. Even in remote locations, such as the Grand Canyon National Park, light pollution from nearby cities like Los Angeles can affect the darkness of the night sky.

To truly escape light pollution, one must venture far away from major interstates and highways, as well as populated areas. In the continental USA, some of the best spots for avoiding light pollution include central and northern Nevada, southwestern New Mexico, northern Arizona, eastern Oregon, and certain parts of other mid-western states. These areas offer a better chance of experiencing a stellar night sky similar to what our ancestors witnessed before the widespread light pollution of modern times.

However, it's important to note that even in less populated regions, light pollution can still be an issue. Factors such as weather conditions, humidity, and the direction of the closest light dome can influence the amount of light pollution in an area. Additionally, light pollution maps can be useful tools for identifying locations with minimal light pollution, but they may sometimes underestimate the brightness of certain sites.

To fully appreciate a dark sky, it's recommended to move away from highways and major sources of light pollution. Even a short distance can make a significant difference. For example, residents of small towns may only need to drive 15-30 minutes to find themselves in an area free from light pollution. Additionally, certain natural phenomena, such as thick morning fog in the valleys, can occasionally create darker skies, even in locations typically affected by light pollution.

In conclusion, to avoid light pollution from towns and cities, one should aim for locations far from major population centres and highways. Utilizing tools like light pollution maps and considering factors such as weather and natural phenomena can help identify optimal spots for stargazing and astronomy.

Weather conditions

Clouds can either blot out the stars or enhance the effect of sky glow, depending on the presence of artificial light. In pristine areas without light pollution, clouds block the stars and create the darkest nights. However, in urban and suburban areas with artificial lighting, clouds reflect and scatter light, intensifying the sky glow and making truly dark nights rare. The optical properties of clouds, including their ability to reflect and scatter light, contribute to this phenomenon.

Air quality and pollution levels also impact light pollution. Deepened air pollution can intensify light pollution, with moderate to severe air pollution increasing night sky brightness by three to ten times. Visibility is another factor influenced by air quality, as haze and smog can reduce visibility and further affect light transmission.

The atmospheric conditions, including the presence of air particles, determine the transmission distance of light. The interaction between light and atmospheric particles influences how far light travels and contributes to the overall light pollution levels.

To minimize the impact of weather conditions on light pollution, some communities are implementing measures such as down-cast lighting and amber-colored lighting. These techniques help reduce the amount of light escaping upward into the sky, minimizing the brightness of sky glow and its various effects on the environment and human health.

Direction of closest light dome

The direction of the closest light dome depends on your location. For example, if you're in Landers, California, about 90 minutes from Los Angeles, you will likely see a light dome from Los Angeles, which washes out a significant portion of the sky.

Similarly, if you're in the San Bernardino Mountains, Idyllwild, or Lockwood Valley near Frazier Park, you will also see a big light dome in the direction of Los Angeles. The same applies if you're in Palomar Mountain, Anza-Borrego (San Diego/Escondido) or the western half of Joshua Tree National Park (Palm Springs and 29 Palms).

If you're in the Grandview campground in Eastern California, you will likely see the Las Vegas light dome, which is visible from 300 km away. The light dome is also visible from Red Rock Canyon near Mojave, Death Valley, the Grand Canyon, and St. George, Utah.

In some cases, the light dome may only be visible on rare nights of exceptional tropospheric clarity. For example, if you're in a hilltop site in the Madawaska Highlands, about 100 km west of Ottawa, you will likely not see the light dome from Toronto, which is 260 km away. However, on rare nights with exceptional tropospheric clarity, the light dome may be visible.

To find the direction of the closest light dome, you can use tools such as light pollution maps or astronomy apps that provide information on light pollution levels and the locations of nearby cities. By identifying the nearest major cities and their directions from your location, you can estimate the direction of the closest light dome. Additionally, you can look for areas with darker skies and less light pollution to minimize the impact of light domes on your observations.

Light pollution ordinances

In the United States, several states and municipalities have recognised the importance of light pollution ordinances and have taken steps to implement them. For example, the Village Board in Illinois passed an ordinance regulating outdoor lighting in December 2007. The state of Illinois also has resources that discuss the factors to consider when regulating light pollution and provide recommendations for improved night preservation practices.

Additionally, the City of Chicago has specific ordinances prohibiting certain types of artificial lighting. These ordinances include restrictions on flashing or revolving lights that resemble emergency vehicles and lights that may interfere with the safe operation of vehicles. Building commissioners are authorised to enforce these ordinances and can order the redirection or covering of lamps or lights that are in violation.

To achieve truly dark skies, it is important to move away from major interstates and highways, as each passing car can ruin the adaptation of the eyes to the dark. While some locations near cities may seem dark, they often still experience significant light pollution that washes out portions of the sky. Therefore, effective light pollution ordinances are crucial for those who wish to experience the stellar night sky views that our ancestors once took for granted.

Frequently asked questions