Eclipse: The passage of one celestial body into the shadow cast by another.
Ecliptic: The track along which the Sun appears to travel around the celestial sphere.
Elongation: The angle between the Sun and a planet or other Solar System, when viewed from Earth.
Equatorial Mounting: One that enables a telescope to be turned around two axes in order to follow the motion of a celestial object across the sky.
Equinox: An occasion when the Sun is vertically overhead at a planet’s equator and day and night have equal duration for the whole planet.
Extrasolar Planet (Exoplanet): A planet that revolves around a star other than the sun.