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Astronomical conjunction

Conjunction is a term used in positional astronomy and astrology. It means that, as seen from some place (usually the Earth), two celestial bodies are at the same position in the sky. Specifically, two planets are in conjunction when the difference between their ecliptic longitudes is 0°. When conjunctions occur, the involved planets are close to one another when viewed upon the celestial sphere.

As seen from a planet that is superior, if an inferior planet is on the opposite side of the Sun, it is in superior conjunction with the Sun. An inferior conjunction occurs when the two planets lie in a line on the same side of the Sun. In an inferior conjunction, the superior planet is "in opposition" to the Sun as seen from the inferior planet.

The terms "inferior conjunction" and "superior conjunction" are used in particular for the planets Mercury and Venus, which are inferior planetss as seen from the Earth. However, this definition can be applied to any pair of planets.

A planet (or asteroid or comet) is simply said to be in conjunction, when it is in conjunction with the Sun, as seen from the Earth. The Moon is in conjunction with the Sun at New Moon (or rather Dark Moon).

Grand Conjunctions

Spring 2002

In Spring 2002, a rare grand conjunction occurred; in which Saturn, Jupiter, Mars, Venus and Mercury were all visible simultaneously in the west-northwest sky, shortly after sundown.

Spring 2000

In May 2000, the 5 brightest planets aligned within 20° of the Sun, as seen from the Earth. This could not be observed because they were too close to the Sun.

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