Light pollution is the change in natural light and dark patterns in nature caused by using artificial lights when they are not needed or used poorly. It is estimated that over 80% of people now live in areas affected by light pollution [1]. But why does it matter? Light pollution affects human health.

High levels of artificial light at night are linked to a greater risk of breast cancer and possibly prostate cancer, as well as more sleep problems, diabetes, obesity, and other heart risks. Recent research also points to harm for mental health, such as depression, mood disorders, and trouble thinking clearly. [2]

Humans are not the only ones affected. Artificial light also affects wildlife, both animals near lights (such as city birds and animals near roads) and those farther away. This happens because of skyglow, when city lights spread and brighten places far from the source. More research shows that both direct and indirect light can change how animals grow, act, and survive. For example, insects are attracted to lights at night [3]. Migrating birds are also affected by light pollution, which can cause them to fly lower and increase the risk of collisions. [4] Sea turtles live in the ocean but hatch at night on the beach. Baby turtles find the sea by seeing the bright horizon over the ocean. Artificial lights pull them away from the ocean. [5]

As of August 2026, about 18,000 satellites are orbiting the Earth [1]. More than half of them belong to the Starlink internet constellation. This number could reach 100,000 in 2030 [2], and even more in the near future with projects such as Space X one million datacenters and Reflect Orbital’s mirror constellation to provide sunlight at night [3]. This poses a serious threat to the darkness and quiet of the night.

The combined light from these satellites decreases the natural darkness of the night sky, affecting both professional astronomy [4] and the cultural traditions associated with stargazing. More than ever, this universal heritage, the dark and quiet sky, is threatened.