Thermosphere
Definition
The hot, thin atmospheric layer from ~50 to 350+ miles up where auroras shine and satellites orbit.
In plain language
Above the mesosphere the air becomes vanishingly thin but very hot. This is aurora country โ and low-Earth-orbit country, which is why big storms that heat and puff up the thermosphere increase drag on satellites.
The science
The thermosphere absorbs solar EUV, with temperatures from ~500 K to 2,000+ K depending on solar activity. Auroral and Joule heating during storms expand it, raising neutral density at satellite altitudes.
Why it matters for aurora viewing
It is the aurora's home layer โ and the reason storm-time headlines mention satellite drag and reentries alongside pretty lights.
See this in action on tonight's data.