An instrument for measuring temperature by utilizing the variation of the physical properties of substances according to their thermal states. Thermometers may be classified into six types according t
o their construction: gas thermometer, liquid-in-glass thermometer, deformation thermometer, electrical thermometer, liquid-in- metal thermometer, and sonic thermometer.
That region of the Earth’s atmosphere where the neutral temperature increases with height. It begins above the mesosphere at about 80-85 km and extends to the exosphere.
An upper part of Earth's Atmosphere that includes the Ionosphere and extends from an altitude of 85 km (above the mesopause), where the temperature is about -33 °C, to the lower level of the Exosphere
at 500 km, where the temperature is about 1,500 °C