What is the X in X-mas?
The region of the Earth's atmosphere lying above the stratosphere and below the thermosphere, from a height of about 50 km (31 mi) to about 80 km (50 mi) above the Earth's surface. In the mesosphere temperatures decrease with increasing altitude due to the decreasing absorption of ultraviolet radiation from the Sun. At the top of this region temperatures are around -95°C (-135.4°F). Most of the meteors that enter Earth's atmosphere burn up while passing through the mesosphere. See also exosphere, stratosphere, thermosphere, troposphere., See illustration at atmosphere.
region of the upper atmosphere between about 50 and 80 km (30 and 50 miles) above the surface of the Earth. The base of the mesosphere is defined as the temperature maximum existing at the top of the stratosphere, with the boundary between the two regions usually called the stratopause. The mesosphere extends upward to the next temperature minimum, which defines the base of the thermosphere; the boundary between the two regions is called the mesopause.