On October 4th, 2004, the United States Postal Service will issue a set of 15 commerative stamps featuring nine cloud formations, to launch National Stamp Collecting Month. The theme for this year is "Reach for the Sky and Collect Stamps!", and was developed in collaboration between The Weather Channel, the American Meteorological Society and the National Oceanic and Atmospheric Administration's National Weather Service, to educate stamp collectors about atmospheric sciences.
"With these spectacular images, we've captured the wonder of nature and the power of the world's weather to shape our lives and our land," said William Johnstone, Secretary, Board of Governors, U.S. Postal Service. "These cloudscapes are beautiful reminders of our ties to the larger environment we live in - an environment of air and water that sustains us all."
Clouds develop when moist air cools to its dew point by rising to a higher altitude or by moving over a cooler surface. Water vapor in the air then condenses in liquid or frozen form around minute particles such as pollen or dust. The shapes and altitudes of clouds, as well as the sequence in which they develop, are a sign of changing weather patterns and aid in forecasts. The prefixes "cirro" and "alto" distinguish high and middle-altitude clouds, respectively.
In the early 19th century, Englishman Luke Howard, chemist by trade and meteorologist by avocation, created a system for classifying clouds using Latin names. He described the three most common shapes as cirrus (curl of hair), stratus (layer) and cumulus (heap); he also defined four compound cloud forms that derive from the three primary shapes, including nimbus (rain). Later scientists added terms such as humilis (small) and incus (anvil) to designate other cloud properties. The International Cloud Atlas, first published in 1896 and last in 1956, is based on this classification system.
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