Greta Jimenez
Light pollution maps are an essential tool for astronomers, both amateur and professional, to find observing sites with minimal light pollution. There are a variety of online resources and smartphone applications that can be used to create light pollution maps, such as Clear Outside, which uses your GPS location to give you a Bortle scale class for your night sky. Light pollution maps are created using data from NASA's Visible Infrared Imaging Radiometer Suite (VIIRS) instrument, which is aboard the NASA/NOAA satellite. This data is then used to calculate the World Atlas of the Artificial Night Sky Brightness, which is a sky brightness map. Users can also add their own SQM measurements to the map.
| Characteristics | Values |
|---|---|
| Map Data Source | NASA VIIRS NTL (2012-2023), VIIRS trend, World Atlas 2015 overlays, observatories and SQM overlay managed by users |
| Map Data Usage | Display light pollution-related content, especially VIIRS/DMSP data |
| Map Data Limitations | Not sensitive to white light from LEDs, commonly used in street lights |
| Map Features | Zenith brightness simulation, find closest dark site, add a map marker, VIIRS statistics per country, show VIIRS/WA values on hover, edit list, etc. |
| Map Usability | Pan and zoom with shift-key and mouse drag, adjust intensity slider |
| Map Tools | Cog wheel for additional options, search field for coordinates, list of locations for quick access |
| Map Data Submission | Contact the website to add a permanent SQM reader to the map |
| Map Data Analysis | Use Lighttrends application for detailed analysis of radiance changes over time |
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What You'll Learn
Using a sky quality meter
A Sky Quality Meter (SQM) is a small device that can measure sky quality, i.e., darkness. It is a popular tool among amateur astronomers as it is affordable and provides quick results that can be easily compared with those of other SQM users. SQM readings are measured in magnitudes per arcsecond squared (mag/arcsec²), with higher values indicating darker skies. SQM readings can be converted into Bortle classes for easier understanding. The Bortle Scale is a standard way to measure how dark the night sky is, ranging from Class 1 (pitch black) to Class 9 (heavily light-polluted).
There are two versions of the SQM: the SQM and the SQM-L, and their readings cannot be compared. To submit your SQM measurements, click on the +SQM icon in the extended toolbar. The time entered should be the local time at which the measurement was taken. SQM-L readings can be sourced from the official Unihedron website.
The SQM product can be further enhanced by using it in conjunction with a Sky Quality Camera (SQC). This is a calibrated Canon dSLR with a fisheye lens bundled with a software suite. It produces a 360-degree all-sky image with MPSAS (magnitudes per square arcsecond) or CCT (color temperature of a black-body radiator) measurements.
SQM measurements can be used to create a light pollution map, which combines light pollution levels with geographical data to help locate ideal spots for Milky Way observation and photography. Light pollution maps can also be used to find the closest dark sky location and how far away it is.
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Utilising online tools
Light pollution maps are a great tool for astronomers, photographers, and anyone looking to observe the night sky. There are several online tools available to create light pollution maps, which can be used to locate dark sites where the sky is unaffected by light pollution.
One such tool is www.lightpollutionmap.info, a mapping application that displays light pollution-related content. The website uses NASA VIIRS NTL (2012-2023) data, VIIRS trend data, World Atlas 2015 overlays, observatories, and SQM overlay managed by users. Users can enter coordinates in "latitude, longitude" format into the "Search" field to locate specific areas. The website also offers additional features such as the ability to create a list of locations, add map markers, and simulate zenith brightness.
Another useful tool is the Light Pollution Map app, available on Google Play. This app helps users locate the darkest possible skies for observing the night sky. It includes features such as cloud cover overlay, temperature information, and the ability to save and load favourite dark sky locations. The app also provides over 100 other astronomy tools, making it a comprehensive resource for astronomers.
For those looking for a more detailed analysis of radiance changes over time, the Lighttrends application is recommended. This application focuses on VIIRS/DMSP data and can provide insights into light pollution trends. Additionally, the Light Pollution Atlas 2022 by "+sbm.authors_name+" is a valuable resource, offering a mirror map with adjustable intensity to compare light pollution colours and road map details.
By utilising these online tools, users can gain valuable information about light pollution levels in specific areas, plan astronomy-related activities, and even contribute their own data to enhance the accuracy of the maps. These tools offer a range of features to cater to different needs, whether it's locating dark skies, analysing radiance changes, or simply exploring light pollution data in an interactive manner.
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Understanding the Bortle scale
The Bortle scale is a nine-level scale that measures the brightness of the night sky and, by extension, the amount of light pollution in a particular location. It was created based on nearly 50 years of observing experience and is useful for comparing observations with light pollution. The Bortle scale has a range of classes, from Class 1, which indicates the darkest sky, to Class 9, which indicates the brightest sky with the most extreme amount of light pollution.
A Class 1 Bortle sky, for example, means that one can observe the Triangulum Galaxy (M33) as a direct-vision naked-eye object. A Class 4 or better rating indicates that a fully dark-adapted observer should be able to spot the Triangulum Galaxy. A Class 8 sky, the second brightest possible, may still allow for astronomy and astrophotography, although the signal will be improved in a lower-class sky.
A light pollution map will often show colours that represent the amount of artificial light in an area, with large cities radiating white to red and rural areas appearing green to blue. The Bortle scale can be used to understand the quality of the night sky in a particular location, although there are other methods for measuring light pollution as well, such as SQM and NELM.
The Bortle scale is a useful tool for astronomers, both amateur and professional, who are concerned about the impact of light pollution on their observations. It provides a consistent standard for comparing sky conditions and can help determine whether a site is dark enough to push equipment to its limits.
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Adjusting map settings
When creating a light pollution map, there are several settings that can be adjusted to customize the map and the data it displays. Here are some options for adjusting the settings:
Map Overlays
The light pollution map can incorporate various overlays that provide additional information. These include the World Atlas 2015 overlay, which is a sky brightness map that indicates the zenith brightness. The NASA VIIRS NTL overlay displays radiance data from 2012 to 2023, showing light sources. The VIIRS Trend overlay offers insights into the trends in radiance data over time. Other overlays like SQM/SQC measurements, Clouds, Aurora Forecast, and IAU observatories can also be included.
Map Display Options
To enhance the visibility of the map, an intensity slider can be adjusted to balance the display of light pollution colours and road map details. Setting the intensity to maximum allows for a comparison of colours to a reference table. Additionally, the map can be viewed in fullscreen mode by clicking the button in the top right corner. Panning and zooming functions are available using the shift key and mouse drag.
Map Features
The map provides the ability to add markers and points of interest. Users can add SQM measurement points and create a list of locations for quick access. The cog wheel icon offers additional options, such as filtering SQM points by name or date. For observatories, there are extra fields to find them and assess their light pollution levels. The legend of the currently visible overlay and feature can be displayed as well.
Map Data Sources
It is important to acknowledge the data sources used for the light pollution map. The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the NASA/NOAA satellite provides valuable radiance data. However, it is not sensitive to white light from LEDs, which may result in underestimating light pollution levels in inhabited areas. The World Atlas 2015 data offers complementary information on zenith brightness.
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Comparing to the World Atlas
The World Atlas is a sky brightness map that tells you how dark the zenith is based on a model calculated from VIIRS data. It is a useful tool for creating a light pollution map as it provides a clear understanding of the artificial night sky brightness in a particular area. The World Atlas 2015, by Fabio Falchi et al., is a detailed resource that presents the world's artificial night sky brightness. This atlas is a valuable reference for light pollution mapping as it provides a comprehensive overview of the brightness of the night sky caused by artificial light sources.
When creating a light pollution map, the World Atlas can be used to identify areas with varying levels of light pollution. By analysing the sky brightness data, you can determine the intensity and extent of light pollution in different regions. This information can then be translated into a visual representation on a map, indicating areas with high, moderate, or low light pollution levels.
Additionally, the World Atlas offers valuable insights into the impact of light pollution on the visibility of celestial bodies. By understanding the zenith's darkness, you can assess how light pollution affects the observation of stars, galaxies, and other astronomical phenomena. This information can be incorporated into the light pollution map, providing a comprehensive understanding of the night sky's visibility in different locations.
Another advantage of using the World Atlas for creating a light pollution map is the ability to compare and contrast light pollution levels over time. By referencing the World Atlas 2015 and comparing it with more recent data, you can identify areas that have experienced changes in light pollution levels. This longitudinal analysis allows for the identification of regions where light pollution has improved or deteriorated, providing valuable insights for conservation efforts and urban planning.
The World Atlas, therefore, serves as a crucial resource for creating a comprehensive and informative light pollution map. By utilising its sky brightness data, insights into celestial visibility, and the ability to conduct longitudinal comparisons, you can develop a detailed understanding of light pollution patterns and their impact on the night sky. This knowledge can then be effectively communicated through a light pollution map, raising awareness and informing decisions that promote dark sky preservation and responsible lighting practices.
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Frequently asked questions
A light pollution map is a tool that displays light pollution-related content. It uses data from the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the NASA/NOAA satellite to show light pollution levels across a specific area.
A light pollution map uses radiance maps, such as VIIRS, to show light sources. It also uses sky brightness maps, such as World Atlas, to indicate how dark the zenith is based on a model calculated from VIIRS data.
The Bortle scale is a way to measure the brightness of the night sky for a particular location, with nine levels ranging from Class 1 (least light pollution) to Class 9 (most extreme light pollution). Light pollution maps often use the Bortle scale to indicate the level of light pollution in a specific area.
To create a light pollution map, you can use a website such as www.lightpollutionmap.info. This website allows you to enter coordinates and plot specific points on the map to get a Zenith sky brightness reading. You can also use a smartphone app, such as Clear Outside by FLO, which uses your GPS location to present a reading on the Bortle scale.
