Something that has long puzzled me is why the study of weather is called "meteorology". One would assume it would be called weatherology. Only recently an answer to this riddle emerged as I explored more about the subject of this column--raindrops. Meteors are literally, "sky events", and the term is most often used to describe objects falling from space. What then are raindrops? Why, "hydrometeors", of course, along with other weather. The study of hydrometeors is, then, "hydrometeorology". Mercifully, the term is shortened to meteorology.

What is known about raindrops is remarkable, even if increasingly common knowledge. Upon closer inspection, raindrops can become awe-inspiring.

Oceans and lakes, soils, plants and even glaciers give off water as a gas. In the atmosphere, this gaseous water, or "water vapor", makes its way until it reaches a place where it is cooled and becomes liquid water again.

This can happen rather quickly, as in the case of rapidly rising air off an ocean, a forest or a lake. It can also happen slowly or in a delayed manner, as in the case of water vapor that crosses hundreds of miles over land from its source to mountains where it is lifted and then cooled. A mass of warmer air colliding with a mass of cooler air also has the effect of cooling some of the warm air.

When it cools in the atmosphere, water vapor "condenses", or begins to become liquid again in the form tiny of droplets. These droplets form around tiny particles of dust and other substances called "condensation nuclei". Billions and billions of tiny droplets form the typical clouds we see. A cloud may contain many thousands of pounds of water in the form of droplets. This doesn't mean that rain will fall. These droplets are so small that they can float on the air. Air is actually quite heavy--about a ton of it rests on your shoulders here near sea level. It happens to be pushing you from all sides so you don't notice.

Only after enough of these tiny droplets have combined and recombined into much larger droplets will the conditions start to be right for rain. Though a droplet will fall as soon as it is large enough to be heavier than air, perhaps as mist, if conditions are right, a droplet can reach a quarter of an inch in size. Warm storms off the ocean here that collide with cool air from the interior can form very large drops and can release large amounts of water.

Much rain is actually melted snow. Snowflakes form from yet another bizarre phenomenon. Cloud droplets that are supercooled, that is, below freezing but still liquid, can evaporate and then refreeze into tiny crystals. A crystal grows larger as more and more vapor freezes onto it. These too, reach a size that is large and heavy enough to drift downward. Much of the time, these snowflakes melt as they fall into warmer air and these drops then fall as rain.

Rain can carry other substances than water. At least 1600 substances, natural and human induced, have been found to ride on the air. Many of these form the nuclei of cloud droplets. "Acid rain" is a serious problem associated with pollution. Most of acid rain results from the burning of fossil fuels that then release oxides of nitrogen and sulfur into the air. These undergo a chemical reaction to form acids that are incorporated in tiny amounts into large numbers of droplets. Of particular concern in the eastern US and Europe, acid rain and snow may be responsible for the severe stress and even destruction of certain forests and lakes as well as corrosion of human structures.

Raindrops have been given a false image. We think of a typical raindrop as a teardrop. In fact, a raindrop is round. If it is large enough, it may have a slightly flattened bottom side. Like most things associated with water, it is not simple to stop raindrops and get a good look. Recent photographic techniques though, have made viewing droplets possible.

Rainbows are perhaps the most fascinating of all. When sunlight strikes a droplet, that droplet acts as both a prism and a mirror. The light is bent or "refracted" on the front of the droplet and spreads into different wavelengths of light--what we see as color. This bent light then bounces off the back of the droplet and shines forward. When we view a rainbow we are standing near the source of the light, and seeing it reflected back from numerous droplets. The composite effect of all these tiny prisms and mirrors is that we see bands of the colors of the light source, in this case the sun.

As the weeks of rainy weather move upon us, it is interesting to note that rain is in fact a chorus of tiny miracles. Drop by drop, it renews life, and at times for most of us, it inspires awe at the wonders of nature that are all around us.