Glossary of astronomy - E

Early-type star is a hotter and more massive star, in contrast to late-type stars that are cooler and less massive. The term originated from historical stellar models that assumed stars began their early life at a high temperature then gradually cooled off as they aged. It can be used to refer to the higher temperature members of any particular population or category of stars, rather than just all stars in general.

Eccentricity is a parameter that determines how much an orbit deviates from a perfect circle. For an elliptical orbit, the eccentricity ranges from greater than zero to less than one.

Ecliptic plane, or plane of the ecliptic, is the plane defined by the Earth's orbit around the Sun. Hence, the position of the Sun as viewed from Earth defines the intersection of this plane with the celestial sphere. The ecliptic plane is used as a reference plane for describing the position of other Solar System bodies. It differs from the celestial equator because of the axial tilt of the Earth.

Effective temperature of a star or planet is the temperature of an ideal black body that would emit the same total amount of electromagnetic radiation.

Evolutionary track is a curve on the Hertzsprung–Russell diagram that a solitary star, of a particular mass and composition, is expected to follow during the course of its evolution. This curve predicts the combination of temperature and luminosity that a star will have during part or all of its lifetime.[6]

Extinction is the absorption and scattering of electromagnetic radiation by matter (dust and gas) between an emitting astronomical object and the observer. Atmospheric extinction varies by the wavelength of the radiation, with the attenuation being greater for blue light than for red.