While most clouds dwell in the first six miles above the ground, noctilucent clouds form about 50 miles (80.47 kilometers) up, near the top of the mesosphere, where temperatures plunge to a frigid minus 130 degrees Fahrenheit (54 degrees Celsius).

Composed of ice crystals, bright, silvery noctilucent clouds are visible at night because their height above the earth allows them to escape the planets' shadow.