| A | B |
|---|
| GROUNDWATER | Water that fills the cracks and pores in underground soil and rock layers. |
| EVAPORATION | The process by which molecules at the surface of a liquid, such as water, absorb enough energy to change to a gaseous state, such as water vapor. |
| TRANSPIRATION | The process by which plants release water vapors through their leaves. |
| PRECIPITATION | Forms of water such as rain, snow, sleet, or hail that fall from clouds and reach Earth's surface. |
| TRIBUTARY | A stream that flows into a larger stream. |
| WATERSHED | The land area that supplies water to a river system. |
| DIVIDE | A ridge of land that separates one drainage basin or watershed from another. |
| RESERVOIR | A natural of artificial lake that stores water for human use. |
| EUTROPHICATION | The process by which nutrients in a lake build up over time, causing an increase in the growth of algae. |
| IMPERMEABLE | Characteristic of materials through which water does not easily pass, such as clay and granite. |
| WATER TABLE | The top of the saturated zone, or depth to the groundwater in an aquifer. |
| UNSATURATED ZONE | A layer of rock and soil above the water table in which the pores contain air as well as water. |
| AQUIFER | An underground layer of rock or soil that holds water. |
| WETLAND | An area of land that is covered with a shallow layer of water during some or all of the year. |
| WAVE | The movement of energy through a body of water. |
| CREST | The highest point of a wave. |
| WAVELENGTH | The horizontal distance between two wave crests. |
| FREQUENCY | The number of waves that pass a specific point in a given amount of time. |
| TROUGH | The lowest point of a wave. |
| WAVE HEIGHT | The vertical distance from the crest of a wave to the trough. |
| LONGSHORE DRIFT | The movement of water and sediment along a beach caused by waves coming into shore at an angle. |
| RIP CURRENT | A rush of water that flows rapidly back to sea through a narrow opening. |
| TIDES | The daily rise and fall of Earth's waters on shores. |
| SPRING TIDE | A tide with the greatest difference between high and low tide that occurs when the sun and the moon are aligned in a line with the Earth. |
| NEAP TIDE | A tide with the least difference between low and high tide that occurs when the sun and moon pull at right angles to each other. |
| SALINITY | The total amount of dissolved salts in a water sample. |
| CURRENT | A large stream of moving water that flows through the ocean. |
| CORIOLIS EFFECT | The way Earth's rotation makes winds in the Northern Hemisphere curve to the right and winds in the Southern Hemisphere cure to the left. |
| UPWELLING | An upward flow of cold water from the ocean depths. |
| EL NINO | An abnormal climate event that occurs every 2 to 7 years in the Pacific Ocean, causing changes in winds, currents, and weather patterns that can lead to dramatic climate changes. |
| OZONE | A form of oxygen that has three oxygen atoms in each molecule instead of the usual two. |
| WATER VAPOR | The invisible, gaseous form of water. |
| POLLUTANT | Harmful substance in the air, water, or soil. |
| DENSITY | The amount of mass in a given space; mass per unit volume. |
| PRESSURE | The amount of force pushing on a surface or area. |
| AIR PRESSURE | A force that is the result of the weight of a column of air pushing down on an area. |
| BAROMETER | An instrument used to measure changes in air pressure. |
| ANEROID BAROMETER | An instrument that measures changes in air pressure without using liquid. Changes in the shape of an airtight metal box cause a needle on the barometer dial to move. |
| TROPOSPHERE | The lowest layer of Earth's atmosphere, where weather occurs. |
| STRATOSPHERE | The second-lowest layer of Earth's atmosphere; the ozone layer is located in the upper stratosphere. |
| MESOSPHERE | The middle layer of Earth's atmosphere; the layer in which most meteoroids burn up. |
| THERMOSPHERE | The outermost layer of Earth's atmosphere. |
| ELECTROMAGNETIC WAVES | A form of energy that can travel through space. |
| RADIATION | The direct transfer of energy through empty space by electromagnetic waves. |
| INFRARED RADIATION | A form of energy with wavelengths that are longer than visible light. |
| ULTRAVIOLET RADIATION | A form of energy with wavelengths that are shorter than visible light. |
| GREENHOUSE EFFECT | The process by which heat is trapped in the atmosphere by water vapor, carbon dioxide, methane, and other gases that form a "blanket" around Earth. |
| THERMOMETER | An instrument used to measure temperature, consisting of a thin, glass tube with a bulb on one end that contains a liquid (usually mercury or alcohol). |
| CONDUCTION | The transfer of heat from one substance to another by direct contact of particles of matter. |
| CONVECTION | The transfer of heat by movements of a fluid. |
| ANEMOMETER | An instrument used to measure wind speed. |
| SEA BREEZE | The flow of air from an ocean or lake to the land. |
| LAND BREEZE | The flow of air from land to a body of water. |
| RELATIVE HUMIDITY | The percentage of water vapor in the air compared to the maximum amount the air can hold at that temperature. |
| PSYCHROMETER | An instrument used to measure relative humidity, consisting of a wet-bulb thermometer and a dry-bulb thermometer. |
| CUMULUS CLOUDS | Clouds that form less than 2 kilometers above the ground and look like fluffy, rounded piles of cotton. |
| STRATUS CLOUDS | Clouds that form in flat layers. |
| CIRRUS CLOUDS | Wispy, feathery clouds made mostly of ice crystals that form at high levels, above about 6 kilometers. |
| TROPICAL | A warm air mass that forms in the tropics and has low air pressure. |
| POLAR | A cold air mass that forms north of 50° north latitude or south of 50° south latitude and has high air pressure. |
| MARITIME | A humid air mass that forms over oceans. |
| CONTINENTAL | A dry air mass that forms over land. |
| FRONT | The area where air masses meet and do not mix. |
| OCCLUDED | Cut off, as the warm air mass at an occluded front is cut off from the ground by cooler air beneath it |
| CYCLONE | A swirling center of low air pressure. |
| ANTICYCLONE | A high-pressure center of dry air. |
| TORNADO | A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth's surface, usually leaving a destructive path. |
| HURRICANE | A tropical storm that has winds of 119 kilometers per hour or higher; typically about 600 kilometers across. |
| FLASHFLOOD | A sudden, violent fold that occurs within a few hours, or even minutes, of a heavy rainstorm. |
| METEOROLOGIST | Scientists who study the causes of weather and try to predict it. |
| ISOBAR | Lines on a map joining places that have the same air pressure. |
| ISOTHERM | Lines on a map joining places that have the same temperature. |
| CLIMATE | The average, year-after-year conditions of temperature, precipitation, winds, and clouds in an area. |
| TROPICAL ZONE | The area near the equator, between about 23.5° north latitude and 23.5° south latitude. |
| POLAR ZONE | The areas near both poles, from about 66.5° to 90° north and 66.5° to 90° south latitudes. |
| TEMPERATE ZONE | The area between the tropical and polar zones, from about 23.5° to 66.5° north and 23.5° to 66.5° south latitudes. |
| TUNDRA | A polar climate region, found across northern Alaska, Canada, and Russia, with short, cool summers and bitterly cold winters. |
| PERMAFROST | Permanently frozen soil found in the tundra climate region. |
| ICE AGE | Cold time periods in Earth's history, during which glaciers covered large parts of the surface. |
| CHLOROFLUOROCARBONS | Chlorine compounds formerly used in air conditioners, refrigerators, and spray cans; also called CFCs. |
| AXIS | An imaginary line that passes through Earth's center and the North and South poles, about which Earth rotates. |
| ROTATION | The spinning motion of a planet about its axis. |
| REVOLUTION | The movement of an object around another object. |
| SOLSTICE | The two days of the year on which the noon sun is directly overhead at either 23.5° South or 23.5° North. |
| EQUINOX | The two days of the year on which neither hemisphere is tilted toward or away from the sun. |
| SOLAR ECLIPSE | The blocking of sunlight to Earth that occurs when the moon is between the sun and Earth. |
| LUNAR ECLIPSE | The blocking of sunlight to the moon that occurs when Earth is directly between the sun and moon. |
| CRATER | A round pit on the moon's or other surface, created by a force of impact. |
| ELECTROMAGNETIC RADIATION | Energy that travels through space in the form of waves. |
| SPECTRUM | The range of wavelengths of electromagnetic waves. |
| SPECTROGRAPH | An instrument that separates light into colors and photographs the resulting spectrum. |
| LIGHT-YEAR | The distance that light travels in one year. |
| NEBULA | A large amount of gas and dust in space, spread out in an immense volume. |
| SUPERNOVA | The explosion of a dying giant or supergiant star. |
| BLACK HOLE | The remains of an extremely massive star pulled into a small volume by the force of gravity. |
| SPIRAL GALAXY | A galaxy whose arms curve outward in a pinwheel pattern. |
| ELLIPTICAL GALAXY | A galaxy shaped like a flattened ball, containing only old stars. |
| BIG BANG | The initial explosion that resulted in the formation and expansion of the universe. |
