Free Astronomy Magazine March-April 2023

6 MARCH-APRIL 2023 ASTRO PUBLISHING A stronaut photographs of parts of Calgary (Canada) show examples of how lighting has changed from 2010-2021: New lighting has been installed and many streetlights have been converted from orange high pressure sodium to white LED. While the photos weren’t taken at the same settings, the noticeable decrease in brightness in the 2021 photo isn’t that much when measured from the surface. The transition to LEDs hasn’t actually reduced the skyglow. [Earth Science and Re- mote Sensing Unit, NASA Johnson Space Center, georeferencing by GFZ Potsdam] decades with data collected by the citizen science project “Globe at Night” (www.globeatnight.org ), started in 2006 by the National Optical-Infrared Astron- omy Research Laboratory (NOIRLab) of the U.S. National Science Foun- dation. This project has so far produced over 200,000 skyglow esti- mates in nearly 20,000 different locations on all continents. The project participants observe the starry sky (without the Moon) from their own location, compare what they see with eight refer- ence celestial charts of various constellations, and via an online form com- municate which of the charts has the most cor- respondence with their observed sky. Taken as a whole, the network of “citizen scientists” func- tions as a global sensor H ong Kong has been named the worst city in the world for light pollution. The commercial and residential areas of Mong Kok, Tsim Sha Tsui and Causeway Bay appear to be the most polluted areas. An infinite number of light sources, many of which use LED technology, make the Hong Kong sky much brighter than that of other metropolises. [Istock.com/Leeyiutung] bit, cannot do with the same effi- ciency. The only satellite that be- tween 1992 and 2013 collected in- formation also useful for evaluating the light emission from the ground (as part of the Defense Meteorolog- ical Satellite Program) was not in- tended for research purposes and the data it provided were not easy to interpret for scientific purposes. Furthermore, in urban centers, the data provided was often “satura- that allows evaluation of the sky- glow exactly at the wavelengths of visible light, something that elec- tronic sensors, especially those in or-