The atmosphere at rest

Abstract

Planet Earth is shaped like a sphere slightly flattened at the poles. Its average radius is about 6370 km and the perimeter at the equator is nearly 40 000 km. The atmosphere, filled with this marvelous gaseous mixture that we call air, is its outer envelope where humanity lives along with numerous species of animals and plants. We ceaselessly breathe this air, move in it, look through it, and we accept the vagaries of weather. As familiar as it seems to us, as indispensable to life as it may be, do we really know this atmosphere? The knowledge gained through the centuries and refined with ever greater precision during the aerospace age gives us now a good knowledge of this medium and allows us to understand its main properties. Let us set off on its observation then, limiting ourselves in this chapter to a first approximation: that of an atmosphere at rest.

The air is full of the shudders of things that flee.

(Charles Baudelaire, Parisian Scenes)