Clouds form when the temperature of the air reaches the condensation point, which is
the point at which water vapor (which is an invisible gas) becomes a liquid. When it reaches
this point, the liquid collects on the dust particles in the air and become visible.
We call the results clouds, unless the clouds form at the ground surface, in which case we call it fog.
Various factors influence the exact point at which condensation can occur, such as the air pressure
at a given altitude, the moisture content of the air, and the air temperature. In most cases, air temperature
is the most important factor.
Clouds held a particular fascination for a young Englishman named Luke Howard (1773-1864).
His father had sent him to grammar school at Burford, a village to the west of London. But Luke was
more interested in the books about nature than in volumes of the Greek and Latin classics.
Before 1800, observers spoke of clouds only as "essences" floating in the sky. Clouds had no names
and were not well understood. The nature and behavior of atmospheric gases, such as oxygen and nitrogen,
were just being investigated in the laboratories of Great Britain and Europe.
In Luke Howard's school years, high-level dust from volcanic eruptions in Iceland and Japan caused
brilliant sunrises and sunsets. To Howard's logical mind, clouds and complicated halos must be the
result of cause and effect in the natural order. Luke wanted to know more.
At the age of 20, Howard returned to London to work as a pharmacist. As a hobby, he joined a group
of scientists, known then as "natural philosophers," who called themselves the Askesians (searchers after
knowledge). Each member, in turn, read a scientific paper to the others. Luke Howards turn came one night
during the winter of 1802-03. His paper was titled, "On the modification of clouds." In our current language,
modification means classification. This paper was so well received that it was published and it has
become a classic in the history of science. Today we still use the basic scheme that Howard presented that night
and the Latin names he assigned to the clouds.
What are the different classifications of clouds?
Howard noted that there are three basic shapes to clouds:
- heaps of separated cloud masses with flat bottoms and cauliflower tops, which he named
cumulus (Latin for heap);
- layers of cloud much wider than they are thick, like a blanket or a mattress, which he named
stratus (Latin for layer);
- wispy curls, like a childs hair, which he called cirrus (Latin for curl).
To clouds generating precipitation, he gave the name nimbus (Latin for rain).
Clouds are found in three layers in the lower atmosphere. Thus, with four types of clouds and three layers,
we come up with 12 major cloud types that have evolved from Howard's pioneering work.
- Heaps:Cumulus family
- Fair weather cumulus
- Swelling cumulus
- Cumulus congestus
- Layers: Stratus family
- Stratus
- altostratus
- cirrostratus
- Layered Heaps
- stratocumulus
- altocumulus
- cirrocumulus
- Precipitating clouds
- cumulonimbus
- cirrus
- nimbostratus
How can I find out more about clouds?
There is a lot of information on the internet regarding clouds. The link provided below is only
one of the locations elsewhere on the web where you can find more information regarding clouds.
www.weather.gov 
