Free Astronomy Magazine March-April 2023

MARCH-APRIL 2023 T raveling through eight different locations, from the urban area of San Jose in California to a desolate stretch of Death Valley, “Lost in Light” explores the ubiquitous but often overlooked phenomenon of light pollution. As artifi- cial light illuminates the night sky, we increasingly lose sight of stars, planets and nebulae, as well as the sense that we are part of a large galaxy and an even larger universe. Showing eight different “levels” of light pollution across California and Oregon, Sriram Murali uses timelapse with dramatic effect, ask- ing what else we lose when we can no longer see the stars. [Sriram Murali] C ape Town, South Africa, was once the center of astronomy in the Southern Hemisphere, whereas now the stars are barely visible. This was the city’s central business district in 2019. [Reuters/Mike Hutchings] ted” (too much light for the modest sensors of that satellite) and there- fore each year invariably showed the maximum value that the sensor could reach. Things improved in late 2011 with NASA’s launch of the Suomi Natio- nal Polar-orbiting Partnership, a weather satellite operated by the National Oceanic and Atmospheric Administration that is still opera- tional. One of Suomi’s onboard in- struments, the Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band, provides data that can be used in artificial lighting monitoring, with a resolution down to a few hundred meters. However, the VIIRS data alone does not pro- vide a true picture of the extent of the skyglow, and this essentially for two reasons. The first is attributable to the fact that the instrument prefe- rably records vertically radiated light, such as that emitted by spherical outdoor lamps, by floodlights, bright outdoor spotlights, and by all other light sources not shielded upwards. The second reason is that VIIRS sen- sors are blind to wavelengths be- low 500 nanometers, the very wave- lengths that host the peak emission of LED lights (400-500 nanometers) and which, moreover, are the ones that most effectively diffuse in the lo- wer atmosphere. These wavelengths