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More generally, in particular in the case of two planets, it means that they just have the same right ascension (and hence the same hour angle). When conjunctions occur, the involved planets are close to one another when viewed upon the celestial sphere. The vast majority of the cases, one of the planets will appear to pass north or south of the other.

Much more rarely, one planet may occult, or cross directly in front of another as seen from Earth, so that the two planets merge into a single object, i.e. they also have the same declination. Some historians believe that the Star of Bethlehem was caused by an occultation of Saturn by Jupiter. More frequent is an occultation of a planet by the Moon, which will generally occur every few years on average (and is often visible only from certain locations and not everywhere the two objects are above the horizon at the time).

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 SunThe Sun (also called Sol is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally capt. In an inferior conjunction, the superior planet is "in oppositionOpposition is a term used in positional astronomy and astrology. It means that, as seen from some place (usually the Earth), one celestial body is opposite to another in the sky. Specifically, two planets are in opposition to each other when their eclipti" to the Sun as seen from the inferior planet.

The terms "inferior conjunction" and "superior conjunction" are used in particular for the planets MercuryMercury is the closest planet to the Sun, and the second-smallest planet in the solar system. Mercury ranges from 0. 5 in apparent magnitude; Mercury is sufficiently "close" to the Sun that telescopes rarely examine it (the greatest elongation is 28. and VenusVenus is the second planet from the Sun, named after the Roman goddess Venus. It is a terrestrial planet, very similar in size and bulk composition to Earth; it is sometimes called Earth's "sister planet" as a result of this similarity. Although all plane, which are inferior planets as seen from the Earth. However, this definition can be applied to any pair of planets.

A planet (or asteroidAn asteroid is a small, solid object in our Solar System, orbiting the Sun. An asteroid is an example of a minor planet (or planetoid , which are much smaller than planets. The asteroids are believed to be remnants of the protoplanetary disc which were no or cometHalley's Comet nucleus sunlit from the left. A comet is a relatively small astronomical object similar to an asteroid but composed largely of ice. In Earth's solar system, the orbits of comets may extend past that of Pluto; of the comets which enter the i) is simply said to be in conjunction, when it is in conjunction with the SunThe Sun (also called Sol is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally capt, as seen from the Earth. The Moon is in conjunction with the Sun at New Moon (or rather Dark Moon).

Strictly speaking one must distinguish between a conjunction in ecliptic longitude and a conjunction in right ascension. Both events need not take place at the same time. It is possible that two celestial bodies come together in conjunction in right ascension but do not reach a conjunction in length and vice versa.

"Quasi-conjunctions" are also possible; in this scenario, a planet in retrograde motion - always either Mercury or Venus - will "drop back" in right ascension until it almost allows another planet to overtake it, but then the former planet will resume its forward motion and thereafter appear to move back ahead of it. This will occur in the morning sky, before dawn; or the reverse may happen in the evening sky after dusk, with Mercury or Venus entering retrograde motion just as it is about to overtake another planet. The quasi-conjunction is reckoned as occurring at the time of the closest actual approach of the two planets.