In Earth’s atmosphere, the boundary between the mesosphere and thermosphere is called the mesopause.
The mesopause is usually the coldest atmospheric layer, with temperatures near 85 kilometres above Earth’s surface sometimes falling below −90°C. Above it, temperatures begin rising through the thermosphere because of the absorption of high-energy solar radiation by sparse atmospheric gases.
The mesopause is not at one perfectly fixed altitude. Its height and temperature vary with latitude, season, time of day, and solar activity. In general, it occurs around 80–หย? kilometres above the surface, although atmospheric scientists use measurements and models to identify its changing position.
It is often confused with the stratopause, which separates the stratosphere and mesosphere, or the tropopause, which separates the troposphere and stratosphere. The mesopause is also distinct from the thermopause, the approximate upper boundary of the thermosphere.