Northern Europe at night

This image of Copenhagen, Denmark and its surroundings was taken by an astronaut on the International Space Station in 2012. Earth Day is held each year 22 April to support environmental protection.

Copenhagen is considered to be one of the most ecological cities in the world but this image shows the reach of human influence on our fragile planet.

The light visible from 400 km above Earth reveals the human footprint on land. The yellow light is wasted energy from houses, factories and streetlights. This energy is not only a nightly drain on resources but also interferes with nocturnal wildlife.

The green hue surrounding our globe is the aurora – our atmosphere protecting us from harmful solar radiation. The blue–white band below is the light from the setting Sun.

That thin layer is all we have to protect us from solar winds, cosmic rays, ultraviolet light and the vacuum of space. We had better take good care of it.