Kiera Jefferson
Light pollution is a common issue for astronomers and astrophotographers, and it can be challenging to escape, even in remote locations. The Bortle Scale, with 9 levels, is often used to measure light pollution, with Bortle 1 skies being free of light pollution and Bortle 4-5 locations offering better viewing conditions. To avoid light pollution, it is recommended to distance oneself from major interstates and highways, as car headlights can interfere with dark adaptation. Additionally, light pollution maps can be referenced to identify areas with less light pollution, such as central and northern Nevada, southwestern New Mexico, and eastern Oregon. However, it is challenging to completely escape light pollution, and even at 25 miles (40 km) away, its effects may still be evident.
| Characteristics | Values |
|---|---|
| Bortle Scale | 9 levels, with level 1 being the least light pollution and level 9 being the most |
| Optimal Bortle Scale level for viewing the sky | Level 3 or lower |
| Light pollution sources | Cities, towns, highways, neighbours' lights |
| Distance from light pollution sources | At least 40 km, but light pollution may still be evident; optimal distance varies depending on the size of the population and direction of the light source |
| Factors affecting light pollution | Weather conditions such as humidity, rainfall, and snowfall; distance and direction of the closest light dome |
| Techniques to escape light pollution | Drive at least 45 minutes out of the city into remote, mountainous, or desert areas; find dark zones or level 1 zones on light pollution maps |
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What You'll Learn
The Bortle Scale measures light pollution on a scale of 1-9
The Bortle Scale is a nine-level classification system that measures the brightness of the night sky at a particular location, with Class 9 denoting the highest degree of light pollution. John E. Bortle developed the scale in 2001 to help amateur astronomers assess the darkness of an observing site. It is based on practical celestial observations and estimates the overall sky brightness.
A Bortle Class 1 sky, the least polluted, offers a truly dark sky experience. In such conditions, your surroundings may only be visible as silhouettes, even with eyes adjusted to the dark. Certain celestial objects, such as the Triangulum Galaxy (M33), can be observed with the naked eye under these conditions. However, a perfectly black sky from horizon to zenith is unattainable due to the Earth's atmosphere.
Locations with a Bortle rating of 4 to 5, like Big Bear in the eastern San Bernardino Mountains, still offer a better viewing experience than more light-polluted areas. However, light domes from nearby cities can wash out significant portions of the sky. An example of a Bortle 3 zone is Cottonwood Campground in Joshua Tree National Park, where light pollution from nearby towns is evident but provides a "dark enough" sky for activities like imaging.
To truly escape light pollution, one must move away from major interstates and highways, allowing their eyes to adapt to the dark without the glare of passing cars. The Bortle Scale aids in understanding light pollution maps and can guide stargazers to locations with optimal viewing conditions.
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Light pollution can be visible from 25 miles away
Light pollution is a growing problem for astronomers and stargazers, with even Bortle 2 skies shrinking. Light pollution can be visible from 25 miles away, and it is a common misconception that pulling off a highway in the desert will offer a truly dark sky. In fact, you need to get away from major interstates and highways so your eyes can adapt to the dark. Each passing car will ruin your night vision, and glare from headlights will illuminate the surrounding area. Even in remote locations, like national parks, light pollution from distant cities can wash out significant portions of the sky.
For example, Big Bear in the eastern San Bernardino Mountains is a Bortle 4-5 location, which is much better than a Bortle 1 location, which has almost no light pollution. However, a big light dome is still visible from Los Angeles, and this light pollution washes out a large part of the night sky. The same is true of Palomar Mountain, Anza-Borrego, Joshua Tree National Park, and other locations.
To find truly dark skies, you need to head to remote locations, far from major cities. In the continental USA, some of the best spots are in central and northern Nevada, southwestern New Mexico, northern Arizona, eastern Oregon, and central Idaho. These locations are far from major interstate highways, which helps reduce light pollution.
Cottonwood Campground in Joshua Tree National Park is a Bortle 3 zone, which is better than Bortle 4-5 skies. However, light pollution is still evident from nearby towns, and portions of the sky are washed out. This is a common issue, as urban sprawl continues to grow, and previously dark skies are now illuminated by light pollution.
To truly escape light pollution, you need to find remote locations, far from any major sources of artificial light. This can be challenging, as even in rural areas, light pollution from distant cities can still be visible, impacting the darkness of the night sky.
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Light domes can wash out parts of the sky
Light pollution is a growing concern for astronomers and stargazers, with the proliferation of cheap and efficient LEDs allowing blue-white light to spread across the sky. This light pollution can form a light dome that washes out parts of the sky, even in remote locations.
A light dome is caused by the scattering of light by particles in the atmosphere, such as moisture and dust. The bright skyglow from city lights can easily wash away the night sky, making it difficult to see stars and other celestial objects. This effect is more pronounced with bluer light, which has a shorter wavelength that is more easily scattered by the molecules in the Earth's atmosphere, resulting in more of the sky being washed out.
Locations like Big Bear in the eastern San Bernardino Mountains, Idyllwild, or Lockwood Valley near Frazier Park are considered better for stargazing, with a Bortle Scale rating of 4-5. However, a significant portion of the sky can still be washed out by light pollution from nearby cities like Los Angeles. Similarly, Palomar Mountain, Anza-Borrego, and parts of Joshua Tree National Park may be dark and remote, but light pollution from nearby metropolitan areas can still impact the visibility of the night sky.
To truly escape light pollution, one must move away from major interstates and highways, as the glare from passing cars can ruin the adaptation of the eyes to the dark. Even in locations far from cities, light pollution from gas stations and other sources can create a light dome that affects the visibility of the night sky.
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Light pollution maps can help find darker locations
Bortle 1 locations, which are the darkest, are almost entirely free of light pollution, with no light domes from cities or nearby villages. In these places, your surroundings may only be visible as silhouettes, even when your eyes have adjusted to the darkness. Such places are rare, but in the continental USA, central and northern Nevada, southwestern New Mexico, northern Arizona, and eastern Oregon offer good chances of finding them.
Bortle 3 locations, like Cottonwood Campground in Joshua Tree National Park, offer a good balance between darkness and convenience. While there is still some light pollution evident, your eyes will need to adjust to the darkness, and you may need a red light to navigate.
Bortle 4-5 locations, like Big Bear in the eastern San Bernardino Mountains, Idyllwild, or Lockwood Valley near Frazier Park, are still much better than urban areas. However, you will still experience light pollution that washes out a significant portion of the sky.
To truly experience a dark sky, it is important to get away from major interstates and highways, as the glare from passing cars can ruin your night vision. Light pollution maps, combined with the Bortle scale, can help you find the darkest locations for stargazing and astronomy.
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Drive away from lights and into nature for better sky viewing
Light pollution from towns and cities can make it difficult to view the night sky, affecting stargazers and astronomers alike. To escape light pollution, you can drive away from urban areas and into nature to find better sky-viewing spots. Here are some tips to guide you on your journey:
Distance from Light Pollution
A good rule of thumb is to get as far away as possible from major interstates and highways, as well as artificial light sources. Ideally, aim for locations that are approximately 50 to 150 kilometers away from city lights. In the continental USA, places like central and northern Nevada, southwestern New Mexico, northern Arizona, and eastern Oregon offer better chances of finding dark skies.
Understanding Light Pollution Maps
Utilize resources such as the Bortle Scale and light pollution maps to assess the level of light pollution in potential viewing spots. The Bortle Scale rates locations from 1 to 9, with lower numbers indicating less light pollution. Additionally, websites like Light Pollution Map or DarkSiteFinder can help you locate dark-sky areas near you.
Choosing the Right Spot
Look for certified Dark Sky Parks, Reserves, or Sanctuaries, which are specifically designated for their low light pollution. These locations will provide you with amazing views of the night sky. If you're unable to travel far, even a short drive out of a well-lit urban area can make a significant difference. Pulling off to the side of a highway in a desert region, for example, can already offer a better sky-viewing experience.
Planning Your Trip
Use tools like PhotoPills to plan your trip precisely. This website can help you determine the best locations and times to view the night sky, including the position of the Milky Way in the sky on a particular night. Additionally, consider the phase of the moon and try to plan your trip during a new moon or when the moon is below the horizon to minimize natural light interference.
Equipment and Techniques
To enhance your sky-viewing experience, consider using equipment such as telescopes, binoculars, or light pollution filters. These tools can help you see a greater number of celestial objects even in areas with some light pollution. Additionally, allow your eyes time to adapt to the darkness, usually around 30 minutes, and minimize any artificial light sources during this period.
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Frequently asked questions
It depends on where you are. Light pollution can be imagined as a bright blurry dome over a city that prevents starlight from shining through. The further you are from the source of light pollution, the less effect it has. However, light pollution can be seen from space, so it's best to look for dark zones or level 1 zones on the Bortle scale.
The Bortle scale measures the amount of light pollution on a scale from 1-9. A Bortle 1 sky is almost entirely free of light pollution, whereas a Bortle 4-5 sky is still usable for astrophotography, but parts of the sky will be washed out.
Bortle 1 skies are typically found in remote, rural areas. In the continental USA, you may find them in central and northern Nevada, southwestern New Mexico, northern Arizona, eastern Oregon, and central Idaho.
You can use light pollution maps to determine the Bortle rating of a particular area. You can also estimate by staying at least 5 miles from a town of 100, 20 miles from a population of 1,000, or 50 miles from a population of 10,000.
If you cannot travel far from light pollution, you can still mitigate its effects. Avoid major interstates and highways, as your eyes will need time to adjust to the dark. You can also use narrowband filters instead of broadband filters when imaging in light-polluted areas.
