Rain forms on planets besides Earth. On Saturn's moon Titan, precipitation is not water, but methane. Titan received so much rain in 2009 that a new methane lake, four times as large as Yellowstone National Park, was formed.
It may not rain cats and dogs, but sometimes it rains tadpoles and tiny fish. This strange meteorological event is probably caused by waterspouts, basically tornadoes that form over water.
Waterspouts start out as vortexes, or columns of rotating, cloud-filled wind. As the vortex descends over an ocean or lake, small aquatic animals may be swept up in the waterspouts funnel.
Changes in pressure and wind force the waterspout to change back into a low-lying cloud, emptying precipitationincluding any creatures swept up in the waterspoutover a nearby landmass.
In 1894, newspapers in Bath, England, reported a rain of tadpoles. In 2009, a storm brought a rain of minnows down on Ishikawa, Japan.
Rain is liquid precipitation: water falling from the sky. Raindrops fall to Earth when clouds become saturated, or filled, with water droplets. Millions of water droplets bump into each other as they gather in a cloud. When a small water droplet bumps into a bigger one, it condenses, or combines, with the larger one. As this continues to happen, the droplet gets heavier and heavier. When the water droplet becomes too heavy to continue floating around in the cloud, it falls to the ground.
Human life depends on rain. Rain is the source of freshwater for many cultures where rivers, lakes, or aquifers are not easily accessible. Rain makes modern life possible by providing water for agriculture, industry, hygiene, and electrical energy. Governments, groups, and individuals collect rain for personal and public use.
Raindrops condense around microscopic pieces of material called cloud condensation nuclei (CCN). CCN can be particles of dust, salt, smoke, or pollution. Brightly colored CCN, such as red dust or green algae, can cause colored rain. Because CCN are so tiny, however, color is rarely visible.
When rain forms around certain types of pollutants, such as sulfur dioxide and nitrogen oxide, the CCN react with water to make the rain acidic. This is called acid rain. Acid can harm plants, aquatic animals like fish and frogs, and the soil. Sulfur dioxide and nitrogen oxide can be released into the atmosphere naturally, such as through a volcanic eruption. These pollutants can also be released by human activity, such as the burning of fossil fuels.
Burning fossil fuels can influence rain patterns. In urban areas, where many vehicles are on the road at once, rainfall is more likely during the weekend than during the week. This is because during the week, millions of cars release exhaust into the atmosphere, creating billions of CCN in the clouds. By the end of the week, clouds are much more likely to be saturated with moisture and CCN. Rain is up to 25 percent more likely on a Saturday than on a Monday in some urban areas.
Scientists have developed a process called cloud seeding to "plant" CCNs in clouds to cause rain. Cloud seeding would reduce drought, although there is very little evidence that it works yet.
Although most people think raindrops look like teardrops, they actually look more like chocolate chip cookies. Like raw balls of dough dropped on a cookie sheet, the smallest raindrops, up to 1 millimeter in diameter, are actually spherical. At 2 millimeters raindrops start to flatten, because of the air pressure pushing up on them as they fall to Earth. This effect is increased at 3 millimeters, and depressions form on the bottom of the drops as the air pushes up on the drops harder. At 4 millimeters raindrops actually distort into a shape that looks like a parachute. When they get to be about 4.5 millimeters in diameter, raindrops are so big that they break apart into two or more separate drops.
Raindrops measure 0.5 millimeter (.02 inches) in diameter or larger. Drizzle, which is smaller than rain, consists of drops smaller than 0.5 millimeter. Most of Earth's precipitation falls as rain.
Raindrops often begin as snowflakes, but melt as they fall through the atmosphere. Snow forms in the same way rain does, but in colder conditions.
Rain falls at different rates in different parts of the world. Dry desert regions can get less than a centimeter (0.4 inches) of rain every year, while tropical rain forests receive more than a meter (3.2 feet). The world record for the most rain in a single year was recorded in Cherrapunji, India, in 1861, when 2,296 centimeters (905 inches) of rain fell.
Term Part of Speech Definition Encyclopedic Entry access Noun
ability to use.
chemical compound that reacts with a base to form a salt. Acids can corrode some natural materials. Acids have pH levels lower than 7.
acid rain Noun
precipitation with high levels of nitric and sulfuric acids. Acid rain can be manmade or occur naturally.
the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).
Encyclopedic Entry: agriculture air pressure Noun
force pressed on an object by air or atmosphere.
animal rain Noun
phenomenon where small aquatic organisms are swept up by a waterspout and fall as rain.
having to do with water.
an underground layer of rock or earth which holds groundwater.
Encyclopedic Entry: aquifer atmosphere Noun
layers of gases surrounding a planet or other celestial body.
Encyclopedic Entry: atmosphere cloud Noun
visible mass of tiny water droplets or ice crystals in Earth's atmosphere.
Encyclopedic Entry: cloud cloud condensation nuclei (CCN) Plural Noun
microscopic bits of clay, salt, or solid pollutant around which water vapor condenses in clouds to form raindrops.
cloud seeding Noun
process of adding chemical material to clouds in order to make it rain or otherwise control precipitation.
to turn from gas to liquid.
indentation or dip in the landscape.
area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.
Encyclopedic Entry: desert diameter Noun
width of a circle.
very light rain.
period of greatly reduced precipitation.
Encyclopedic Entry: drought dust Noun
tiny, dry particles of material solid enough for wind to carry.
Encyclopedic Entry: dust electrical energy Noun
energy associated with the changes between atomic particles (electrons).
gases and particles expelled from an engine.
fossil fuel Noun
coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.
water that is not salty.
science and methods of keeping clean and healthy.
activity that produces goods and services.
body of water surrounded by land.
large area of land.
person who studies patterns and changes in Earth's atmosphere.
chemical compound that is the basic ingredient of natural gas.
very small fish.
nitrogen oxide Noun
one of many chemical compounds made of different combinations of nitrogen and oxygen.
device which allows a person to glide down safely from a great elevation.
small piece of material.
chemical or other substance that harms a natural resource.
introduction of harmful materials into the environment.
Encyclopedic Entry: pollution precipitation Noun
all forms in which water falls to Earth from the atmosphere.
Encyclopedic Entry: precipitation rain Noun
Encyclopedic Entry: rain rain dance Noun
spiritual or ritual dance performed to bring rain.
drop of liquid from the atmosphere.
rain forest Noun
area of tall evergreen trees and a high amount of rainfall.
large stream of flowing fresh water.
Encyclopedic Entry: river salt Noun
mineral often used as a preservative or flavoring.
to fill one substance with as much of another substance as it can take.
sixth planet from the sun.
gases given off by a burning substance.
precipitation made of ice crystals.
precipitation that falls as an ice crystal.
rounded and three-dimensional.
sulfur dioxide Noun
greenhouse gas that can cause acid rain.
stage in a frog or toad's development when the animal has gills and a tail, but not limbs.
largest moon of the planet Saturn.
a violently rotating column of air that forms at the bottom of a cloud and touches the ground.
existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.
urban area Noun
developed, densely populated area where most inhabitants have nonagricultural jobs.
Encyclopedic Entry: urban area volcanic eruption Noun
activity that includes a discharge of gas, ash, or lava from a volcano.
an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.
Encyclopedic Entry: volcano vortex Noun
column of rotating fluid, such as air (wind) or water.
column of rotating cloud-filled wind that descends to an ocean or lake.
Encyclopedic Entry: waterspout