It has been suggested that this article be merged with Appulse. (Discuss) Proposed since December 2007.
Conjunction is a term used in positional astronomy and astrology. It means that, as seen from some place (usually the Earth), two celestial bodies appear near one another in the sky. The event is also sometimes known as an appulse.
The astronomical and astrological symbol of conjunction is ☌(in Unicode x260c) and handwritten:
Three consecutive days of close conjunction between the Moon and Venus.
Passing close
More generally, in the particular case of two planets, it means that they merely have the same right ascension (and hence the same hour angle). This is called conjunction in right ascension. However there is also the term conjunction in ecliptical longitude. At such conjunction both objects have the same ecliptical longitude. Conjunction in right ascension and conjunction in ecliptical longitude do not normally take place at the same time, but in most cases nearly at the same time. However at triple conjunctions, it is possible that a conjunction only in right ascension (or ecliptical length) occur. At the time of conjunction - it does not matter if in right ascension or in ecliptical longitude - the involved planets are close together upon the celestial sphere. In the vast majority of such cases, one of the planets will appear to pass north or south of the other.
Passing closer
However, if two celestial bodies attain the same declination at the time of a conjunction in right ascension (or the same ecliptical latitude at a conjunction in ecliptical longitude), the one that is closer to the Earth will pass in front of the other. In such a case, a syzygy takes place. If one object moves into the shadow of another, the event is an eclipse. For example, if the Moon passes into the shadow of Earth and disappears from view, this event is called a lunar eclipse. If the visible disk of the nearer object is considerably smaller than that of the farther object, the event is called a transit. When Mercury passes in front of the Sun, it is a transit of Mercury, and when Venus passes in front of the Sun, it is a transit of Venus. When the nearer object appears larger than the farther one, it will completely obscure its smaller companion; this is called an occultation. An example of an occultation is when the Moon passes between Earth and the Sun, causing the Sun to disappear either entirely or partially. This phenomenon is commonly known as a solar eclipse (though the term is a misnomer). Occultations in which the larger body is neither the Sun nor the Moon are very rare. More frequent, however, is an occultation of a planet by the Moon. Several such events are visible every year from various places on Earth.
Position of the observer
The term conjunction primarily refers to a phenomenon defined only for the position of the observer, not just to a celestial relationship. However, e.g. for moon and sun observed from the earth, conjunction as a classifying term may apply both to the positions of conjunction (both sun and moon observed jointly in one direction or with similar ecliptical longitude) and to opposition (both sun and moon observed separately in opposite directions or with ecliptical longitude 180 degrees apart).
Triangular conjunction formed by the Moon, Venus (left) and Jupiter, seen from Sao Paulo, Brazil, on 1 December2008.Moon, Venus and Jupiter formed a smile face :) seen from Eastern Asia
2008
On 1 December2008, Venus, Jupiter, and the crescent moon converge in a rare conjunction to form a tight triangle in the evening after sunset, visible worldwide. It was similar to a happy "V" face, or a frowning face.[1]
2007
A very remarkable planetary/galactic configuration occurred on 23–24 December2007. The configuration on December 23 — Mars, Earth, Sun, Mercury, Jupiter, Galactic Centre — is shown in the graphic simulation linked below; it becomes even more remarkable in that it will be accompanied by the Full Moon (conjunct Mars) at about 2 a.m. on December 24 when a simultaneous Venus square Neptune occurs. It is even more remarkable in that the Pluto/Sun conjunction appears exactly on the Winter Solstice, just past conjunction with the Galactic Centre.
Solar System on 22 December2007. What is not shown is Pluto (which would be to Jupiter's right) Saturn, which follows down from Venus, and Uranus and Neptune. Saturn and Neptune form the cross's t-member. It is a 23/12 configuration. There will be a full moon on 23 December2007.
2002
In late April 2002, a rare grand conjunction occurred; in which Saturn, Jupiter, Mars, Venus and Mercury were all visible concomitantly in the west-northwest sky, shortly after sundown; this will happen again in early July 2060, except that on that occasion the quintet will be bunched in the east-northeast sky, shortly before dawn.
2000
In May 2000, the five brightest planets aligned within 20° of the Sun, as seen from the Earth. This could not be observed since they were too close to the Sun.
1987
On August 241987, the five objects closest to Earth — the Sun, Moon, Mercury, Venus and Mars — were within approximately 5° of one another, the Sun setting first, followed by Mars, Venus, Mercury and the Moon, in that order, within 20 minutes. As in the 2000 conjunction above, this event was unobservable due to the Sun being part of the line-up.
1962
During the new moon and solar eclipse of February 4–5, 1962, an extremely rare grand conjunction of the classical planets occurred (it included all five of the naked-eye planets plus the Sun and Moon), all of them within 16° of one another on the ecliptic. At the precise moment of the new moon/solar eclipse, five celestial bodies (the Sun, Moon, Mercury, Venus, and Jupiter) were clustered within 3° of each other, with the Earth in close conjunction with them. Taken in totality though, this grand conjunction included the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn, with the Earth also in alignment with the Sun and Moon at the exact moment of the new moon/solar eclipse (eight celestial bodies in total).
1899
During the new moon on December 2–3, 1899, a near-grand conjunction of the classical planets and several other binocular bodies occurred. The Sun, Moon, Mercury, Mars and Saturn were all within 15° of each other, with Venus 5° ahead of this conjunction and Jupiter 15° behind. Accompanying the classical planets in this grand conjunction were Uranus (technically visible unaided in pollution-free skies) Ceres and Pallas.
Conjunctions of planets in right ascension 2005-2020
Cazimi (an extremely close conjunction involving the Sun, when a planet is conjoined with the Sun within 17 arc minutes of exactitude from the center of the solar disc)
Combust (a moderate to close conjunction involving the Sun and another planet, though it is not as close as Cazimi)