Thermosphere gas and the ionospheric plasma. The International Space Station orbits the Earth within the middle of the thermosphere, between . It is convenient to separate the atmospheric regions according to the two temperature minima at about 12 km altitude (the tropopause) and at about 85 km (the mesopause) (Figure 1). The thermosphere (or the upper atmosphere) is the height region above 85 km, while the region between the tropopause and the mesopause is the middle atmosphere (stratosphere and mesosphere) where absorption of solar UV radiation generates the temperature maximum near 45 km altitude and causes the ozone layer. The density
The empire on which the sun never sets at the present time." In 1821, the "Caledonian Mercury" wrote of the British Empire, "On her dominions the sun never sets; before his evening rays leave the spires of Quebec, his morning beams have shone three hours on Port Jackson, and while sinking from the waters of Lake Superior, his eye opens upon the Mouth of the Ganges." Daniel Webster famously expressed a similar idea in 1834: "A power which has dotted over the surface of the whole globe with her possessions and military posts, whose morning drumbeat, following the sun and keeping company with the hours, circles the earth