A

Altostratus (As)

One of the 10 characteristic cloud types (or cloud genera) recognised by the International Cloud Atlas. Its name comes from altum (height) and stratus (spread out). It appears as a greyish or bluish sheet of cloud, partly or totally covering the sky, but with parts sufficiently thin to at least vaguely reveal the sun.

Alpine glow

A beautiful illumination effect seen in mountainous regions around sunset, beginning when the sun is around 2º above the horizon. At its most spectacular, snow-covered mountains in the east assume vivid tones of yellow, pink and purple.
 

Air

The mixture of gasses that make up the Earth’s atmosphere. Excluding water vapour and dust, the main components of air are nitrogen, oxygen, argon, carbon dioxide, neon, helium, krypton, hydrogen, xenon and ozone.