An Etymological Dictionary of Astronomy and Astrophysics
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The position of a planet when it can be seen in the western sky just after sunset.

→ eastern; → elongation.

1) Increase in length per unit of original length.
2) The angular distance of a planet from the Sun as seen from the Earth. An elongation of 0° is called → conjunction; one of 180° is called → opposition; and an elongation of 90° is called → quadrature.

→ elongate; → -tion.

The Greatest → elongation of an inferior planet occurring after sunset.

Superlative of → great; → eastern; → elongation.

The largest → elongation of an inferior planet from the Sun. It may be → greatest eastern elongation or → greatest western elongation. The greatest elongation of Mercury is about 28°, and thus Mercury can only be observed 112 minutes after sunset or before sunrise. For Venus, it is about 47°, making it visible at most about 3 hours after sunset or before sunrise.

Superlative of → great; → eastern; → elongation.

The Greatest → elongation of an inferior planet occurring before sunrise.

Superlative of → great; → western; → elongation.

The position of a planet when it is visible in the eastern sky before dawn.

→ western; → elongation.