What is Elongation?
[[Image:Positional astronomy.png|thumb|350px|This diagram shows the elongations (or angle) of the Earth's position from the Sun.]] '''Elongation''' is an [[astronomy|astronomical]] term that describes the angle between the [[Sun]] and a [[planet]], as viewed from [[Earth]]. When an [[inferior and superior planets|inferior planet]] (Mercury or Venus) 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 (planet)|Mercury]], is between 18° and 28°; and for [[Venus (planet)|Venus]] between 45° and 47°. This value varies because the orbits of the planets are [[elliptical]], rather than perfect circles. [[Category:Celestial mechanics]] {{Sci-stub}}