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Space and Solar Definitions - E

E - Exa, a multiplier, x1018 from the Greek "hex" (six, the "h" is dropped). The reference to six is because this is the sixth multiplier in the series k, M, G, T, P, E. See the entry for CGPM.

E Region - A daytime layer of the earth's ionosphere roughly between the altitudes of 85 and 140 km.

Earth - Third planet from the sun, a terrestrial planet.

Eccentricity - The distance between the foci of an ellipse divided by the major axis.

Ecliptic - The plane in which Earth orbits the sun and in which solar and lunar eclipses occur.

EDR - Experiment Data Record.

EHz - ExaHertz (1018 Hz)

EL - Elevation.

Ellipse - A closed plane curve generated in such a way that the sums of its distances from the two fixed points (the foci) is constant.

ELV - Expendable launch vehicle.

EM - Electromagnetic.

Emerging Flux Region (Efr) - An area on the sun where new magnetic flux is erupting.

EMF - Electromagnetic force (radiation).

EMR - Electromagnetic radiation.

EOT - End Of Track, used in DSN operations.

Equator - An imaginary circle around a body which is everywhere equidistant from the poles, defining the boundary between the northern and southern hemispheres.

Equinox - The equinoxes are defined as the time when day and night are of equal length. The vernal equinox marks the beginning of spring in the northern hemisphere, and the autumnal equinox marks the beginning of autumn in the northern hemisphere.

ERC - NASA's Educator Resource Centers.

ERT - Earth-received time, UTC of an event at DSN receive-time, equal to SCET plus OWLT.

Eruptive - Solar activity levels with at least one radio event(10cm) and several chromospheric events per day (class c flares)

Eruptive Prominence On Limb (Epl) - A solar prominence that becomes activa- ted and is seen to ascend from the sun.

ESA - European Space Agency.

ET - Ephemeris time, a measurement of time defined by orbital motions. Equates to Mean Solar Time corrected for irregularities in Earth's motions. Obsolete, replaced by TT, Terrestrial Time.

eV - Electron volt, a measure of the energy of subatomic particles.

Extra solar planet - A planet orbiting a star other than the sun.

Extreme Ultraviolet (Euv) - A portion of the electromagnetic spectrum from approximately 100 to 1000 angstroms.

Extremely Low Frequency (Elf) - That portion of the radio frequency spectrum from 30 to 3000 hertz.

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