People have looked up to the sky at night for millennia. Some have searched the stars for the answer to the question “where are we going?” sometimes figuratively (astrology), and literally (for navigation). In the 20th century, the stars started to disappear from the night sky, as glow from electric lights in cities outshone them. These days, some citizen scientists are looking to the night sky to find out whether the widespread adoption of LED lighting is making the problem of skyglow worse or better.
In many citizen science projects, the main or only role of participants is to collect data. We wanted to change that for our project, and put the data and tools to analyze it back into the hands of the public. Our new web application, my sky at night, does just that.
The image below shows skyglow data collected in Europe from four different sources: visual observations from our Loss of the Night app (LON), visual observations from the Globe at Night project (GAN), observations with the Dark Sky Meter app for iOS (DSM), and observations taken by citizen scientists with a Sky Quality Meter (SQM). You can filter by year and project to decide which data to show in your browser (selecting all data will take a while to download, clicking on “load only displayed area” will help speed this up).
At wide zoom levels, the blue circles show how many observations were taken at that location. A red point indicates the sky brightness in terms of the naked eye limiting magnitude (NELM) in an area with a single observation. The higher NELM is, the more stars you can see.
Clicking on a point or circle will bring up more information. For our app data (LON), the user’s entire observation is displayed (see below). You can see which stars the participant was able to see (yellow for bright stars, orange for faint stars, dark orange for averted vision stars), as well as the stars that they couldn’t see (gray for unsure, black for not visible). The graph also shows our best estimate for the NELM as a bar with an uncertainty band. In the case below, we estimate the NELM to be 3.67±0.1.
These graphs will allow project participants to examine how accurate their own data is. We hope that this motivate them, by showing how as they develop practice using the app they begin to take more accurate data. Anyone who has provided us with their email address within the app can also view all of his or her own measurements, by clicking on the “My Measurements” tab at the top.
Of course, the big question is “How is the sky changing?” We’ve designed a tool that lets you select a region and display the average of observations taken in multiple years. The figure below shows the trend observed by the Globe at Night project in one neighborhood of Tucson, Arizona.
The Globe at Night project goes back the longest (since 2006). Unfortunately, individual Globe at Night observations aren’t very precise, so for a neighborhood with well-established lighting that doesn’t change much year-to-year, it will probably take many years (maybe even decades), to see a clear local trend in GAN data. However, when you use myskyatnight to look at different neighborhoods in the same city, you can see very clear differences between the suburbs and the city center. So assuming that the sky is changing, it will just a matter of time before such trends will show up in the Globe at Night data, even at the local scale (so keep taking data!).
The LON, DSM, and SQM data are more precise than GAN, so it shouldn’t take long before we will see clear changes in some areas, especially places that have a full-city conversion to LEDs. Since the LON and DSM projects have only been running since 2013, the first trends should start to become visible in the next few years.
We hope that by providing this way for citizen scientists to access their data, they will be more likely to continue participating in the future. After all, the very best results come when citizen scientists make multiple observations from the same location each year! We also hope that this data will start to feed back into local decisions about outdoor lighting. In the ideal case, we will find examples of success stories: cities that invest in environmentally friendly lighting and end up seeing more stars above well-lit sidewalks.
More information about the project is available in the “about” tab at my sky at night. The web application was funded under the MYGEOSS project, which received funding from the European Union’s Horizon 2020 research and innovation programme. The web application code is available under the EUPL. The programing was done by Interactive Scape GmbH. The Loss of the Night app development was funded by the German Ministry of Education and Research.
Christopher Kyba studies the ecological impact of artificial light in the nighttime environment at the German Research Center for Geoscience (GFZ) in Potsdam. His work mainly focuses on quantifying the flux of light emitted upward by cities (using aerial or satellite observations), and the light that is returned back to Earth as skyglow. One of his current research interests is in examining observations made by citizen scientists in order to understand how skyglow is changing with the introduction of LED lamps.