A binary star system in which the stars eclipse each other.
ecliptic
The apparent path of the Sun around the sky.
electromagnetic radiation
Changing electric and magnetic fields that travel through space and transfer energy from one place to the other; examples are light or radio waves.
electron
Low-mass particle carrying negative charge.
enzyme
Special protein that controls processes in an organism.
ESA
European Space Administration.
event horizon
The boundary of the region of a black hole from which no radiation may escape. No event that occurs within the event horizon is visible to a distant observer.
evolutionary track
The path a star follows in the H-R diagramm as it gradually changes its surface temperature and luminosity.
extrasolar planet
A planet in orbit around a star other than the Sun.