A visible collection of minute particle matter, such as water droplets and/or ice crystals, in the free air. A cloud forms in the atmosphere as a result of condensation of water vapor. Condensation nuclei, such as in smoke or dust particles, form a surface upon which water vapor can condense.
THE CLOUD CLASSIFICATION GROUPS
Our modern-day cloud classificaton system divides clouds into five (5) groups according to their shape, structure, and height above the ground.
Cloud heights are determined by the heights of their bases, except within the heap clouds group (group 1) where the heights are determined by the cloud tops.
An excellent site to view the most unusual cloud formation is called Spacious Skies, I think if you visit it and have an interest in cloud formation you will enjoy it.
Fog can be considered as a low stratus cloud in contact with the ground. When the fog lifts, it usually becomes true stratus. This photo shows fog over the Pemigewasset River basin with clear skies elsewhere.
Fog
This photo and information was obtained from an excellent site:
The aurora borealis (northern lights), and the aurora australis (southern lights) are beautiful, dynamic, luminous displays seen in the night sky in the northern and southern latitudes, near the poles.
The aurora is a very large-scale phenomenon encircling the entire polar regions, but when one views a particular display from the ground only a very small portion is visible. Most aurora have basically a curtainlike or ribbonlike form. As the auroral activity increases, folds develop, the complexity and extent of the folds depending on the degree of activity. Astronauts looking down on the polar region are in a much better position than those of us who are earthbound to observe the aurora.
Though the aurora appear to come near to the ground, the light originates high in the atmosphere. The lowest aurora are about 100 kilometers or 62 miles above the ground, with the highest extending to 4 times that distance. This is much higher than clouds or the highest flying aircraft (besides the Space Shuttle).
