Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Light pollution. Light pollution results from the excess of artificial light produced by human endeavours mainly as a side effect of industrialisation. This kind of pollution is usually most noticeable around well populated areas associated with intense human activities, such as street lighting, lights from the transportation system, buildings and houses. But it can also come from other places, such as ships and oil platforms in the sea. This image taken in a national park in Belgium in 2018 shows the detrimental effect of light pollution on the most precious resource that connects all humans together – the night sky.
Credit: Dong Han/IAU OAE

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Light pollution. This composite image taken in Slovakia in 2020 illustrates the effect due to artificial illumination of light polluted areas. The higher the level of light pollution, the less we can observe in the sky, notice how the number of stars visible even to a sensitive digital camera decreases from right to left. Light pollution not only affects the visibility of objects in the night sky, but also significantly impacts ecosystems, negatively affecting many animals, such as migratory night birds, which may encounter difficulties to find the direction to where they should migrate to, or the sea turtles, which may be confused by the lights from coastal cities located near the beaches where they are supposed to spawn. Light pollution can also negatively impact some human health. Therefore, it is important to preserve the dark and quiet night sky for the benefit of the entire planet and all the diverse life it supports.
Credit: Tomáš Slovinský/IAU OAE

Caption: Third place in the 2021 IAU OAE Astrophotography Contest, category Light pollution. This image of Venus and the Pleiades also shows the tracks of the Starlink satellites. These satellites which are located at an altitude of approximately 550 kilometres, are part of an ever-growing constellation of satellites aimed to provide worldwide internet access. The reflective surfaces of the satellites, coupled with the fact that they are orbiting around the Earth, means that astronomical observations which require very long exposures capture “tracks” of the satellites in their images. Astronomical images used for scientific research are not usable because the measurements and data will contain these “tracks”. Because the number of satellites is expected to grow, it is likely that in the near future there will be no place on Earth where these satellites will not be visible crossing the sky. This is a new type of light pollution that seems to be an upcoming problem we will have to deal with, as these satellites might prevent optimal observation of the sky.
Credit: Torsten Hansen/IAU OAE