In this breathtaking photograph we see the crescent moon through the top of Earth’s atmosphere. The image was taken above 21.5°N, 113.3°E by International Space Station crew Expedition 13 on July 20, 2006 over the South China Sea, just south of Macau.

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth’s gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km (62 mi), or 1.57% of the Earth’s radius, is often used as the border between the atmosphere and outer space. [Source]