Weather

Weather can be defined as the condition of the atmosphere at any given time and place. Weather conditions are determined by six major factors: air temperature, air pressure, humidity of the air, amount and kind of cloud cover, amount and kind of precipitation, and speed and direction of the wind. Weather condition patterns for any one region or for the whole planet can be charted on a weather map containing information about all six of these factors. This information often can be used to produce a weather forecast, a prediction of weather conditions at some future time for some given region.

The study of weather is known as meteorology. No exact date can be given for the beginnings of this science, since humans have studied weather conditions for many centuries. Indeed, the word meteorology itself goes back to Meterologica, a book written by the Greek natural philosopher Aristotle in about 340 B.C. Many scholars date the rise of modern meteorology to the work of a Norwegian father and son team, Vilhelm and Jakob Bjerknes. The Bjerknes's were the first to develop the concept of masses of air moving across the earth's surface, affecting weather conditions as they moved. They also created the first widespread system for measuring weather conditions throughout their native Norway.

The six factors determining weather conditions result from the interaction of four basic physical elements: the Sun, the earth's atmosphere, the earth itself, and natural landforms on the earth's surface.