Bronte Wells
Light pollution, the human-made alteration of outdoor light levels from those occurring naturally, has become a significant issue in the past few decades. The artificial brightening of the night sky has harmful effects on streetlights, greenhouses, and satellites, among other things. To combat this, areas like the Central Idaho Dark Sky Reserve have been established to protect and prioritize natural darkness. To track and analyze light pollution in these areas, various methods and tools can be used, including digital cameras. One such method is the Sky Quality Camera (SQC), which uses a software program combined with a Digital Single Lens Reflex (DSLR) camera equipped with a fisheye lens to capture and analyze night sky images. In addition to automatic analysis, the SQC can also simulate changes in night sky brightness under different scenarios. Other ways to measure light pollution include using smartphone apps, light pollution filters, and participating in citizen science projects.
| Characteristics | Values |
|---|---|
| Methods | Instrumental and observational methods |
| Equipment | Photometers, digital cameras, smartphones, Sky Quality Camera (SQC), and telescopes |
| Camera features | Monochrome CCD, colour single shot CCD, Digital Single Lens Reflex (DSLR), and fisheye lens |
| Camera settings | Exposure, sensitivity, dynamic range, and white balance |
| Camera accessories | Light pollution filters, scratch-resistant, water-resistant, and slim design |
| Software | Sky Quality Camera (SQC), Dark Sky Meter, and Loss of the Night |
| Image analysis | Brightness, luminance, correlated colour temperature (CCT), sky glow, cloud coverage, and colour accuracy |
| Location | Dark Sky areas, clear view to the south or southwest, and distance from artificial lights |
| Time | After midnight, when street lighting is reduced or turned off |
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What You'll Learn
Using a Sky Quality Camera (SQC)
The Sky Quality Camera (SQC) is a software program that can be used in conjunction with a Digital Single Lens Reflex (DSLR) camera to detect light pollution in the night sky. Developed by Andrej Mohar, the SQC utilises a fisheye lens to capture a hemispherical view of the ground, sky, and horizon when pointed straight up. This ultra-wide-angle lens produces visual distortion, which is beneficial for night sky imaging and analysis.
To use the SQC effectively, several steps must be followed. Firstly, the sky border is defined, and then points are created within this border to differentiate between clear skies and clouds. This process teaches the software to recognise unobstructed areas in the image, which are crucial for accurate night sky brightness analysis. Subsequently, the coordinates and azimuth angles of light pollution sources near the image location are added. The azimuth angle helps determine the direction in which light pollution originates and ends, enabling the software to calculate the specific sources contributing to light pollution in a given area.
Once the SQC has sufficient information, it can perform an automatic analysis of the image. This analysis yields specific details about the sky, including sky brightness (magnitude per arcsecond squared), luminance (microcandela per meter squared), correlated colour temperature (Kelvin), and cloud coverage percentage. The SQC's ''Prediction Simulation' tool further enhances its capabilities by simulating potential scenarios, such as alterations in the percentage of white LEDs or changes in lamp power/quality over time.
The SQC has been utilised in areas like the Central Idaho Dark Sky Reserve to monitor the quality of the night sky and pinpoint sources of light pollution. This tool is essential for preserving dark sky areas and understanding the impact of surrounding artificial lighting. The SQC, in combination with satellite data, provides a comprehensive view of the sky's condition and potential threats, facilitating more effective monitoring and protective measures.
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Understanding light pollution
Light pollution is the human-made alteration of outdoor light levels from those occurring naturally. It is the presence of any unwanted, inappropriate, or excessive artificial lighting. Light pollution is a side effect of industrial civilization, with sources including building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, illuminated sporting venues, and even fireworks.
Light pollution has harmful effects on human health, wildlife behaviour, and our ability to observe stars and other celestial objects. It can interrupt sleep and confuse the circadian rhythm, the internal 24-hour clock that guides day and night activities and affects physiological processes in nearly all living organisms. For example, an increased amount of light at night lowers melatonin production, resulting in sleep deprivation, fatigue, headaches, stress, and anxiety. It can also wreak havoc on the natural body rhythms of both humans and animals, such as migratory birds, pollinators, sea turtles, and other mammals.
Light pollution has become a significant issue in recent decades as the amount of unilluminated territory worldwide dwindles. It is estimated that 83% of the world's people live under light-polluted skies, with more than 80% of the world's population and 99% of Americans and Europeans experiencing sky glow, the brightening of the night sky due to electric lights. This makes it difficult for astronomers and astrophotographers to observe celestial objects and capture clear images of the night sky.
To address light pollution, authorities have taken a variety of measures, ranging from doing nothing to implementing strict laws and regulations specifying how lights may be installed and used. Reducing light pollution can involve simple steps like utilizing light sources of minimum intensity necessary, turning lights off when not needed, adjusting light fixtures or using more appropriate light bulbs. There is also a growing global movement to reduce light pollution, with organizations like DarkSky International working to educate the public, establish codes and statutes, and advocate for legislative change.
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Using a light pollution filter
Light pollution can ruin your night photos, removing all the detail from the sky and reducing the detail in the stars. The glare of light pollution can be a menace for astrophotographers. The good news is that there is a fix for light pollution: a light pollution filter.
A light pollution filter helps reduce light pollution in your images. These filters are specially engineered to cut down on a particular wavelength. They ultimately block out specific colours. Most light pollution filters are set to block out anywhere between 570nm-620nm, which covers the orange and red parts of the spectrum. Most large cities use the same coloured lights, and the engineers of light pollution filters specifically target these colours to be removed. You’ll most commonly see orange and yellow light pollution filters, but you can also get filters that target many other colours.
You can also invest in a clip-in style filter that sits beneath the lens inside the camera body. It is recommended to use the clip-in style filter over a large threaded (77mm, etc.) light pollution filter, as this is a better placement for filtration in the optical train. You are also not paying for a large piece of glass that needs to cover your camera’s objective lens. However, you need to ensure you purchase the correct-sized clip-in filter for your camera body.
It is important to note that the light pollution filter works better under dark skies (in remote locations). Even though it can also be used in (heavy) light-polluted areas, it will still not be possible to capture the Milky Way Galaxy or the Orion Nebula from the centre of a big city simply by attaching a light pollution filter to your lens. When used correctly, however, the filter can be a fantastic tool for improving your nighttime photos by countering the problem of light pollution.
Some examples of light pollution filters include the Hoya Starscape Light Pollution Filter, the K&F Concept Clear Natural Night Filter, and the NiSi 100mm Natural Filter for Nighttime Light Pollution.
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Adjusting camera settings
Adjusting your camera settings is key to detecting night sky light pollution. The camera's sensitivity is important, as a more sensitive camera will require a shorter exposure to detect faint details. Monochrome CCD cameras are more sensitive than DSLR cameras, and have a greater dynamic range, meaning they can detect a larger range of luminosity.
When using a DSLR, a fisheye lens can be useful for night sky imaging and analysis. The ultra-wide angle of the lens allows the camera to capture a hemispherical view containing the ground, sky, and horizon when pointed straight up.
To capture the colour of images, filters are required. Red, green, and blue (RGB) filters are designed to approximate the colour sensitivity of the human eye, so the resulting image is true to colour. However, when using RGB filters to create a broadband image, all types of wavelengths are captured across the entire visible spectrum, picking up a lot of light pollution from surrounding city lights. This can be mitigated by using a CLS CCD light pollution filter, which can remove a tremendous amount of sky glow.
If you are shooting in a designated Dark Sky area, light pollution filters are less necessary, but they can still improve the colour accuracy of your shots by reducing the yellowish haze given off by artificial lighting.
There are a variety of light pollution filters available, which can be purchased at different price points and in different sizes. Some have extra features such as anti-reflective coatings, or are built to be water- or oil-repellent.
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Locating dark skies
The impact of light pollution is such that the night sky over many cities is hundreds of times brighter than a natural, starlit sky. This makes it difficult to achieve the main requirement for a good astro image – a high signal-to-noise ratio. As such, it is important to seek out locations with pristine, dark skies.
Dark skies can be found without travelling to far-flung places. The trick is to escape light pollution by finding a spot usually about 50 to 150 kilometres away from city lights. A good view of the night sky can even be found within a city. One can get into the shadow of a brick wall or a tree to block out streetlights, though this may obstruct the view of the sky.
For those seeking to capture the Milky Way, a scenic location with a clear view to the south or southwest is ideal, as this is where the brightest part of the Milky Way will appear. The farther one is from artificial lights, the clearer the view will be.
There are also designated Dark Sky areas, such as the Central Idaho Dark Sky Reserve, which was established to protect the sanctity of the nighttime from light pollution. These locations are ideal for astrophotography as there is very little or no light pollution to interfere with the view.
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Frequently asked questions
There are a few ways to detect night sky light pollution with a digital camera. One way is to use a Sky Quality Camera (SQC), which is a software program combined with a Digital Single Lens Reflex (DSLR) camera equipped with a fisheye lens. The SQC can analyse the quality of the night sky and identify sources of light pollution. Another way is to use a monochrome CCD camera, which is more sensitive than a DSLR camera and can capture both faint and bright details in a single exposure. Additionally, you can use light pollution filters on your digital camera to reduce the impact of light pollution and improve the colour accuracy of your images.
Capturing photos of the night sky in a light-polluted area can be challenging, but there are a few things you can try. First, try to find a spot that is not directly illuminated by street lights, as this can help reduce the amount of light pollution in your photos. You can also use light pollution filters on your camera to reduce the impact of light pollution and improve the colour accuracy of your images. Additionally, try to stay out late, as there is usually less stray light around after midnight. Post-processing can also help to remove some of the light pollution from your images.
There are a few other ways to measure light pollution without a digital camera. You can use a handheld sky quality meter (SQM) device, or you can participate in citizen science projects such as Globe at Night or Cities at Night, which use smartphone apps to collect data on light pollution.
