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Words begining with "E"

Earth Observing System (EOS)

A series of small - to intermediate-sized spacecraft that is the centerpiece of NASAs Mission to Planet Earth (MTPE). Planned for launch beginning in 1998, each of the EOS spacecraft will carry a suite of instruments desiqned to study global climate change. MTPE will use space-, aircraft-, and ground-based measurements to study our environment as an integrated system. Designing and implementing the MTPE is, of necessity, an international effort. The MTPE program involves the cooperation of the U.S., the European Space Agency (ESA), and the Japanese National Space Development Agency (NASDA). The MTPE program is part of the U.S. interagency effort, the Global Change Research Program.

EOS Research

Spacecraft Research purpose

EOS-AM1      Characterization of land and ocean surfaces
(1998)       sea-surface temperature
             terrestrial and ocean productivity
             clouds, aerosols, and radiative balance

EOS-COLOR    ocean color and productivity

EOS-AERO1    atmospheric aerosols and ozone

EOS-PM1      clouds, precipitation, radiative balance,
(2000)       terrestrial snow, and sea ice
             sea surface temperature
             terrestrial and ocean productivity
             atmospheric temperature and moisture

EOS-ALT1     ocean circulation, ice sheet mass balance
(2002)       and land-surtace topography

EOS-CHEM1    atmospheric chemical species and their
(2002)       transformations
             solar radiation
Projected year of launch shown in parentheses

Earth Observing System Data & Information System (EOSDIS)

The system that will manage a dataset of Earth science observations to be collected over a 15-year period. Existing data indicates that the Earth is changing, and that human activity increasingly contributes to this change. To monitor these changes, a baseline of "normal" performance characteristics must be obtained. For the Earth, these baseline characteristics must cover a global scale and a long enough period that the variation caused by seasonal changes and other cyclical or periodic events (e.g., El Nino and the solar cycle) may be included in the analyses. The baseline characteristics also must enable scientists to quantify processes that govern the Earth's system. Functionally, EOSDIS will provide computing and networking facilities supporting EOS research activities, including data interpretation and modeling; processing, distribution, and archiving of EOS data: and command and control of EOS observatories.

Earth Probes

Discipline specific satellites and instruments that will be used by NASA to obtain observations before the launch of EOS spacecraft. Generally smaller than the EOS satellites and instruments, Earth Probes are planned to complement the broad environmental measurements from EOS with highly focused studies in areas such as tropical rainfall (TRMM), ocean productivity (SeaWiFS), atmospheric ozone (TOMS), and ocean surface winds (NSCAT).

Earth Radiation Budget Experiment (ERBE)

An experiment to obtain data to study the average radiation budget of the Earth and determine the energy transport gradient from the equator to the poles. Three satellites were flown in different orbits to obtain the data: the Earth Radiation Budget Satellite, ERBS (launched in October 1984), NOAA-9 (launched in December 1984), and NOAA-I0 (launched in September 1986). See Television and Infrared Observation Satellite (TIROS)

Earth station (aka Ground Station)

Hardware necessary to acquire data directly from environmental satellites. The WEFAX Earth station diagram illustrates a basic ground station configuration for obtaining direct readout data from geostationary environmental (weather) satellites.

Earth System

The Earth regarded as a unified system of interacting components, including geosphere (land), atmosphere (air), hydrosphere (water and ice), and biosphere (life).


Earth's Interacting Componets

  Geosphere     Physical elements of the Earth's
                surface, crust, and interior.
                Processes in the geosphere include
                continental drift, volcanic eruptions
                and earthquakes.
  Atmosphere    Thin layer of gas or air that
                surrounds the Earth. Processes in
                the atmosphere include winds,
                weather, and the exchange of gases
                with living organisms.

  Hydrosphere   Water and ice on or near the surface
                of the Earth. Includes water vapor in
                clouds; ice caps and glaciers, and
                water in the oceans, rivers, lakes, and
                aquifers. Processes in the
                hydrosphere include the flow of
                rivers, evaporation. and rain.
  Biosphere     The wealth and diversity of living
                organisms on the Earth. Processes in
                the biosphere include life and death
                evolution, and extinction.

Earth System Science

An integrated approach to the study of the Earth that stresses investigations of the interactions among the Earths components in order to explain Earth dynamics, evolution, and global change.

Eccentricity (aka ecce or E0 or e)

One of six Keplerian elements, it describes the shape of an orbit. In the Keplerian orbit model, the satellite orbit is an ellipse, with eccentricity defining the "shape" of the ellipse. When e = 0, the ellipse is a circle. When e is very near 1, the ellipse is very long and skinny.


  • e = O = circular orbit
  • O < e < 1 = elliptical orbit
  • e = 1 = parabolic orbit
  • e > 1 = hyperbolic orbit


The partial or total apparent darkening of the sun when the moon comes between the sun and the Earth (solar eclipse), or the darkening of the moon when the full moon is in the Earths shadow (lunar eclipse).

Eclipse Blindness

Focus-point type of vision loss caused by looking at the sun for too long a time, which can burn a hole in the retina of the eye.


Science dealing with the interrelationships between livinq orqanisms and their environments.


Any natural unit or entity including living and non-living parts that interact to produce a stable system through cyclic exchange of materials.

Electromagnetic Radiation

Energy propagated as time-varying electric and magnetic fields. These two fields are inextricably linked as a single entity since time-varying electric fields produce time-varying magnetic fields and vice versa. Light and radar are examples of electromagnetic radiation differing only in their wavelenghts (or frequency). Electric and magnetic fields propaqate throuqh space at the speed of liqht.

Electromagnetic Spectrum

The entire range of radiant energies or wave frequencies from the longest to the shortest wavelengths - the categorization of solar radiation. Satellite sensors collect this energy, but what the detectors capture is only a small portion of the entire electromagnetic spectrum. The spectrum usually is divided into seven sections: radio, microwave, infrared, visible, ultraviolet, x-ray, and gamma-ray radiation.

Electromagnetic Wave

Method of travel for radiant energy (all energy is both particles and waves), so called because radiant energy has both magnetic and electrical properties. Electromagnetic waves are produced when electric charges change their motion. Whether the frequency is high or low, all electromagnetic waves travel at 300,000,000 meters per second.


Producing an electric current through differences in potential.

Electromotive Force

The force that can alter the motion of electricity, measured in terms of the energy per unit charge imparted to electricity passing through the source of this force. Electromotive force causes current flow in a circuit.

Element Set (aka Keplerian elements, classical elements, satellite elements)

Specific information used to define and locate a particular satellite. The set includes the catalog number; epoch year, day, and fraction of day; period decay rate; argument of perigee; inclination; eccentricity; right ascension of the ascending node; mean anomaly; mean motion; revolution number at epoch; and element set number. This data is contained in the two-line orbital elements provided by NASA in the NASA Prediction Bulletin. See Keplerian elements.


The angle at which an antenna must be pointed above the horizon for optimal reception from a spacecraft.

Elliptical Orbits

Bodies in space orbit in elliptical rather than circular orbits because of factors such as gravity and drag. The point where the orbiting satellite is closest to Earth is the perigee, sometimes called peri-apsis or perifocus. The point where the satellite is farthest from Earth is called apogee, apoapsis, or apifocus. A line drawn from perigee to apogee is the line-of-apsides, sometimes called the major-axis of the ellipse. It's simply a line drawn through the ellipse the long way.

El Nino

A warming of the surface waters of the eastern equatorial Pacific that occurs at irregular intervals of 2-7 years, usually lasting 1-2 years. Along the west coast of South America, southerly winds promote the upwelling of cold, nutrient-rich water that sustains large fish populations, that sustain abundant sea birds, whose droppings support the fertilizer industry Near the end of each calendar year, a warm current of nutrient-poor tropical water replaces the cold, nutrient-rich surface water. Because this condition often occurs around Christmas, it was named El Nino (Spanish for boy child, referring to the Christ child). In most years the warming lasts only a few weeks or a month, after which the weather patterns return to normal and fishing improves. However, when El Nino conditions last for many months, more extensive ocean warming occurs and economic results can be disastrous. El Nino has been linked to wetter, colder winters in the United States; drier, hotter summers in South America and Europe; and drought in Africa. See ENSO.


Emergency Locator Transmitter. See Search and Rescue.

Energy Budget

A quantitative description of the energy exchange for a physical or ecological system. The budget includes terms for radiation, conduction, convection, latent heat, and for sources and sinks of energy

ENSO (El Nino-Southern Oscillation)

Interacting parts of a single global system of climate fluctuations. ENSO is the most prominent known source of interannual variability in weather and climate around the world, though not all areas are affected. The Southern Oscillation (SO) is a global-scale seesaw in atmospheric pressure between Indonesia /North Australia, and the southeast Pacific. In major warm events El Nino warming extends over much of the tropical Pacific and becomes clearly linked to the SO pattern. Many of the countries most affected by ENSO events are developing countries with economies that are largely dependent upon their agricultural and fishery sectors as a major source of food supply, employment, and foreign exchange. New capabilities to predict the onset of ENSO events can have a global impact. While ENSO is a natural part of the Earth's climate, whether its intensity or frequency may change as a result of global warming is an important concern.


The complex of physical, chemical, and biological factors in which a living organism or community exists.


See Earth Observing System.


See Earth Observing System Data and Information System.

EPA (Environmental Protection Agency)

U.S. agency that ensures: Federal environmental laws are implemented and enforced effectively; U.S. policy - both foreign and domestic - fosters the integration of economic development and environmental protection so that economic growth can be sustained over the long term; public and private decisions affecting energy, transportation, agriculture, industry, international trade, and natural resources fully integrate considerations of environmental quality; national efforts to reduce environmental risk are based on the best available scientific information communicated clearly to the public; everyone in our society recognizes the value of preventing pollution before it is created; people have the information and incentives they need to make environmentally-responsible choices in their daily lives; and schools and community institutions promote environmental stewardship as a national ethic.


A tabulation of a series of points that define the position and motion of a satellite. See Keplerian elements.


Emergency Position Indicating Radio Beacon See Search and Rescue.

Epoch (aka Epoch Time or TO)

Epoch specifies the time of a particular description of a satellite orbit. See Keplerian elements.


An imaginary circle around the Earth that is everywhere equally distant (90 degrees from the North Pole and the South Pole. The equator is a qreat circle and defines latitude 0 degrees.


See Earth Radiation Budget Experiment.


European Space Agency


The process whereby a body of water becomes rich in dissolved nutrients through natural or man-made processes. This often results in a deficiency of dissolved oxygen, producing an environment that favors plant over animal life.


Change from a liquid (more dense) to a vapor or gas (less dense) form. When water is heated it becomes a vapor that increases humidity Evaporation is the opposite of condensation.


The uppermost layer of the atmosphere, its lower boundary is estimated at 500 km to 1000 km above the Earth's surface. It is only from the exosphere that atmospheric gases can, to any appreciable extent, escape into outer space.

External Forcing

Influence on the Earth system (or one of its components) by an external agent such as solar radiation or the impact of extraterrestrial bodies such as meteorites.


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: May 13 2021

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