Just as the physical body of the earth is comprised of many layers, the earth's atmosphere is also made up of layers. One of these is called the mesosphere. The literal translation is "middle sphere," as it is sandwiched between the major top and bottom layers of the atmosphere. The first layer is the troposphere, the second is the stratosphere, the mesosphere is third, then on top of that is the thermosphere and exosphere. The mesosphere begins approximately 30 miles (48.2 km) above the surface of the earth and extends to approximately 50 miles (80.4 km).
This layer is where most meteors burn up. Though many believe the streaks of light caused by meteors are falling stars, they are actually small pieces of rock or metal that hit earth’s atmosphere at extraordinarily high speeds. The pressure created by this shatters the meteors and causes a transfer of energy from the meteor to the atoms and molecules in the atmosphere. This energy is then released as the “glow” that is mistaken for falling stars.
The top of the mesosphere is the coldest place in the atmosphere, with temperatures falling as low as -225°F (about -143°C). The freezing temperatures cause ice to form on the rock and metal particles in the atmosphere, which can then form what are known as noctilucent clouds. These clouds sit higher than any other clouds in the atmosphere and are only visible when the sun falls below the horizon, and then only near the polar latitudes, during summer months when the mesosphere reaches its coldest temperatures.
Noctilucent clouds have a unique, wave-like appearance, and are illuminated in the evening sky by the sun below. They have only been sighted since the end of the 19th century, but sightings are increasing in frequency and they are thought to be increasing in brightness as well. Scientists believe they may indicate changes in earth’s atmosphere, primarily a change in climate.