As with any field of scientific study, astronomy has a long list of important terminology. So we've put together this glossary where you can check you fully understand the meaning of the common terms, as well as some of the more unusual words.
A -- B -- C -- D -- E -- F -- G -- H -- I -- J -- K -- L -- M -- N -- O -- P -- Q -- R -- S -- T -- U -- V -- W -- X -- Y -- Z
Words beginning with 'E' :
Eccentricity : the measure that determines how much an orbit deviates from a perfect circle. The value ranges from 0 (a perfect circle) to 1 (a parabolic escape orbit. For example Earth's orbital eccentricity is 0.0167 and Pluto's is nearly 0.25.
Eclipse : when an astronomical object is temporarily obstructed either by the shadow of another object or by an object passing in between. A solar eclipse on Earth occurs when the Moon’s shadow and is seen as the Moon blocking the Sun. A lunar eclipse is when Earth’s shadow falls upon the Moon.
Ecliptic : the area of the celestial sphere through which the Sun travels over one year.
Electromagnetic spectrum : the range of frequencies electromagnetic radiation with wavelengths from 10-18 m to 100 km.
Ellipse : an ellipse is the shape obtained by the intersection of a plane (flat surface) with a cone. Most astronomical objects in orbits around another object trace out ellipses.
Elongation : is the degree of separation between the Sun and other Solar System bodies as seen from Earth. It is measure eastward or westward of the Sun. Tree main elongations have names: Conjunction (0°), Quadrature (90°) and Opposition (180°).
Equinox : two days in the year (around 20 March and 23 September) when the day and night are almost the same duration.
Escape velocity : it is the minimum speed required to escape the gravitational influence of an astronomical object. The escape velocity for Earth is 40,270 km/h (25,020 mph).
Event horizon : is the boundary around a black hole from which nothing can escape. Anything past this point would need to travel faster than the speed of light to escape.
Eyepiece : the part of a telescope through which an observer looks. Eyepieces can be changed to offer different magnifications.
To support the quizzes in each section, we've put together some extra resources to provide further information:
- Articles - Alongside the quizzes, you'll find short articles on related topics, to help widen your knowledge of that area.
- Glossary - As with any field of scientific study astronomy has a long list of important terminology. So we've put together a glossary where you can check you fully understand the meaning of the more unusual words!