elongation

n. lengthening, extension, making longer

Elongation is an astronomical term that refers to the angle between the Sun and a planet, as viewed from Earth.When an inferior planet is visible after sunset, it is near its greatest eastern elongation. When an inferior planet is visible before sunrise, it is near its greatest western elongation. The value of the greatest elongation (west or east), for Mercury, is between 18° and 28°; and for Venus between 45° and 47°. This value varies because the orbits of the planets are elliptical, rather than perfect circles.
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Noun
1. the quality of being elongated
(hypernym) longness
(derivation) elongate, stretch
2. an addition to the length of something
(synonym) extension
(hypernym) addition, add-on, improver
(derivation) elongate, stretch
3. the act of lengthening something
(hypernym) change of shape
(derivation) elongate, stretch

n. elongation, extension, stretching

(n.)
The angular distance of a planet from the sun; as, the elongation of Venus or Mercury.
  

(n.)
The act of lengthening, or the state of being lengthened; protraction; extension.
  

(n.)
That which lengthens out; continuation.
  

(n.)
Removal to a distance; withdrawal; a being at a distance; distance.