Helena Joyce
Light pollution is a common issue for astronomers, both amateur and professional. It is caused by inefficient or misused light fixtures that scatter light above the horizontal plane, drowning out the light from faint celestial objects. Light pollution can vary depending on location, with cities being the source of most light pollution problems. Many astronomers use the Bortle scale to classify the level of light pollution in a given location, with Class 1 being excellent dark sky viewing and Class 9 being inner-city sky viewing. While light pollution can impact the visibility of certain objects, it is still possible to get great views of deep-sky objects through a telescope, even in light-polluted areas. The amount of light pollution that is okay for telescope viewing depends on the type of telescope, the targets of observation, and the observer's experience.
| Characteristics | Values |
|---|---|
| Impact of light pollution | Light pollution impacts astronomy by drowning out the light from faint objects like galaxies and nebulae and increasing the brightness of the sky background while viewing faint stars. |
| Avoiding light pollution | Astronomers can avoid light pollution by traveling to dark-sky locations far from cities, the source of most light and air pollution problems. |
| Measuring light pollution | The Bortle scale is a nine-level numeric scale that measures the night sky's brightness in a particular location, quantifies celestial objects' observability under light pollution conditions, and compares the darkness of observing sites. |
| Light pollution and telescopes | Light pollution affects all scopes similarly, but not all targets are affected equally. Planets, for example, are largely unaffected by light pollution. |
| Mitigating light pollution | Using a light pollution filter can help mitigate the effects of light pollution and improve the views of deep-sky objects through a telescope, even from a city. |
| Light pollution and eyes | Light pollution affects the eye's ability to adapt to darkness, making it more difficult to see faint objects in the night sky. |
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What You'll Learn
Using a light pollution filter
Light pollution is unwanted light that projects up into the night sky, drowning out the light from faint objects and increasing the brightness of the sky background. It can be caused by inefficient light fixtures and amplified by air pollution. Astronomers can avoid light pollution by travelling to dark-sky locations, and they often use the Bortle scale to classify the level of light pollution in a particular location.
- The Optolong L-eXtreme Filter: This is a dual-band filter that isolates two important wavelengths of light emitted by many deep-sky objects. It helps to collect images of objects in the night sky with better contrast.
- The Optolong L-eNhance: This filter has a steeper cutoff after the Ha (656nm) bandpass line, which can result in higher contrast images that may look slightly less natural in overall colour.
- The Orion UltraBlock Narrowband Filter: This filter dims the view of all objects slightly but retains more of the Orion Nebula and brings out detail in M43, part of the Orion Nebula complex. It gives a good dark background with a characteristic blue-green hue, and stars still stand out well.
- The Burgess Optical Broadband Nebula Filter: This is a cheaper option that gives reasonable views of the Orion Nebula. The background sky is not as dark as with other filters, but the green-blue hint is also not as overpowering.
- The UHC Filter: This filter is designed to block a lot of light in the green, yellow, and orange wavelengths, while allowing the main nebulae wavelengths through. It is recommended for deep space use with a telephoto lens or telescope.
When using a light pollution filter with a telescope, it is important to consider your observing position. Avoid observing from inside a building with open doors or windows, as escaping warm air will create air currents and cause the view to shimmer. Additionally, try to avoid viewing targets that are directly over rooftops or above hot air vents. Allow your eyes at least 30 minutes to adapt to the darkness, and keep any artificial lights out of your direct line of sight.
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The Bortle scale
The scale ranges from Class 1, which is excellent dark sky viewing with no light interference, to Class 9, which represents inner-city sky viewing where light significantly reduces the number of objects one can see. For example, a Class 1 Bortle sky means that one can observe M33 (Triangulum Galaxy) as a direct-vision naked-eye object. A Class 8 or 9 sky, on the other hand, is an urban sky where many stars making up familiar constellations are invisible, and dim constellations such as Cancer and Pisces are not seen at all.
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The impact of light pollution on different celestial objects
Light pollution is the presence of any unwanted, inappropriate, or excessive artificial lighting. It is a major side effect of urbanization, and it negatively impacts human health, wildlife behaviour, and our ability to observe celestial objects.
The impact of light pollution on celestial objects varies depending on the level of light pollution and the type of celestial object. Light pollution can drown out the light from faint objects like galaxies and nebulae, making them difficult or impossible to observe through a telescope. The Moon, planets, and a few of the brightest star clusters are less affected by light pollution and can often be observed even from light-polluted cities.
The Bortle Dark-Sky Scale, created by American astronomer John E. Bortle, is a nine-level numeric scale that measures the night sky's brightness at different locations. It also quantifies the observability of celestial objects under light pollution conditions. Class 1 on the Bortle scale represents excellent dark sky viewing with no light interference, while Class 9 represents inner-city sky viewing where light significantly reduces the number of objects visible.
Even with light pollution, it is possible to observe some celestial objects through a telescope. A small telescope or binoculars can reveal a respectable number of brighter deep-sky targets, including star clusters, bright planetary nebulae, and summer and winter showpieces like the Orion Nebula and the Lagoon Nebula. Additionally, high-resolution planetary imaging can be successful under light-polluted skies, as some of the best astrophotographers in this field work from urban and suburban locations.
To mitigate the effects of light pollution, astronomers can use light pollution filters, dew shields, and eyepieces with their telescopes. They can also travel to dark-sky locations far from cities, which are the primary sources of light and air pollution. By carefully planning and using the right equipment, it is possible to enjoy stargazing and astronomy even in light-polluted areas.
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The effect of light pollution on your eyes
Light pollution is unwanted light that projects into the night sky, making it much brighter than natural and significantly impacting astronomy and stargazing. It can come from inefficient or misused light fixtures that scatter light above the horizontal plane.
The Bortle scale is a nine-level numeric scale that measures the night sky's brightness in a particular location, allowing astronomers to classify the level of light pollution around them. Class 1 is excellent dark sky viewing with no interfering light, while Class 9 is inner-city sky viewing, where light significantly reduces visibility.
Light pollution not only affects our ability to observe the night sky but also has various effects on human health and safety. Here are some of the impacts of light pollution on the eyes and human health:
- Disability Glare: Bright lights from poorly designed lighting can cause disability glare, a condition so intense that it forces individuals to avert their eyes from the veil of light scattering across their retinas. Disability glare can temporarily impair vision, making everything except the light source virtually invisible. Older individuals are particularly vulnerable to disability glare as their eyes lose the ability to quickly adjust to changing light levels.
- Circadian Rhythm Disruption: Light pollution can disrupt the natural 24-hour day/night cycle, known as the circadian rhythm, which affects various physiological processes in humans, including brain wave patterns, hormone production, cell regulation, and other biological activities. This disruption can lead to insomnia, depression, and an increased risk of cancer, cardiovascular disease, and other health issues.
- Eye Strain and Visual Acuity: Intense, blue-rich LED lighting can decrease visual acuity and cause eye strain. This can create safety concerns, especially when driving or performing tasks that require clear vision.
- Obstructed Night Vision: Excessive light pollution can obstruct night vision, making it difficult to see potential dangers in low-light conditions. This can be a safety hazard for pedestrians, drivers, and anyone navigating in dark environments.
- Health Risks: Research suggests that artificial light at night can negatively impact human health. Light pollution has been linked to increased risks for obesity, depression, sleep disorders, diabetes, and in some cases, breast cancer. Shift work involving circadian disruption has also been classified as a probable carcinogen by the World Health Organization.
To mitigate the effects of light pollution on the eyes and health, it is recommended to use shielded or fully shielded lighting fixtures, dim light levels when possible, and reduce glare. Additionally, proper lighting design can help balance functionality and health considerations.
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Reducing light pollution by travelling to dark-sky locations
Light pollution is the human-made alteration of outdoor light levels from those occurring naturally. It has harmful effects on human health, wildlife, public safety, and energy security. Artificial light at night (ALAN) is the primary driver of light pollution, and it can be worsened by air pollution. Dust and smoke scatter light in all directions, further brightening the sky. Astronomers can avoid light pollution by travelling to dark-sky locations far from cities, the major sources of light and air pollution.
The Bortle scale is a nine-level numeric scale that measures the night sky's brightness in a particular location. It was created and published by John E. Bortle in Sky & Telescope magazine's February 2001 edition. On the Bortle scale, Class 1 is classified as excellent dark sky viewing where no light interferes, and Class 9 is classified as inner-city sky viewing where light significantly reduces the visibility of objects in the sky. Many astronomers use the Bortle scale to classify the level of light pollution in their surroundings.
To reduce light pollution by travelling to dark-sky locations, you can refer to the following tips:
- Identify dark-sky locations by using resources such as the International Dark Sky Places program, which works with communities, parks, and municipalities to certify and protect dark places for humans and wildlife.
- Plan your trip by researching the lighting conditions and any local efforts to reduce light pollution in the area. You can visit the websites of organizations like DarkSky International, which provides information on dark-sky news, events, and advocacy efforts.
- Consider the time of year and the moon phases during your trip. The zodiacal light, which is the light reflected off dust particles in the solar system, is most visible in the spring and autumn and can illuminate the night sky. A new moon phase will also provide darker sky conditions.
- Choose a location that is far from population centres and major sources of light pollution, such as cities or highly lit tourist spots. Look for areas with minimal artificial light, such as nature reserves or remote rural areas.
- Bring appropriate equipment, such as a telescope with a light pollution filter, to enhance your viewing experience. A small telescope or a good pair of binoculars can help you observe brighter deep-sky targets, such as star clusters and bright planetary nebulae.
By following these tips and travelling to dark-sky locations, you can significantly reduce light pollution and improve your stargazing experience.
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Frequently asked questions
Light pollution is unwanted light that projects up into the night sky, making the atmosphere much brighter than the natural night sky. It can come from poorly designed, inefficient, or misused light fixtures that scatter light above the horizontal plane.
Light pollution can significantly impact astronomy by drowning out the light from faint objects like galaxies and nebulae, and increasing the brightness of the sky background while viewing faint stars. The brighter the sky, the fewer objects you will be able to see.
You can use a light pollution filter, which is specifically designed to suppress the glow from artificial light. You can also try to view objects from a darker location, as light pollution varies depending on your surroundings.
