Conjunction (astronomy and astrology)

Conjunction of Mercury and Venus, align above the Moon, at the Paranal Observatory.

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:

Passing close

In the morning of 1 May 2011, about an hour before sunrise, five of our Solar System’s eight planets and the Moon could be seen from Paranal.^[1]

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

In the night sky over ESO's Very Large Telescope (VLT) observatory at Paranal, the Moon shines along with two bright companions: Venus and Jupiter.

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).

Superior and inferior

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 planets as seen from the Earth. However, this definition can be applied to any pair of planets, as seen from the one farther from the Sun.

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).

"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 draw away from it again. 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 (often Mercury and Venus are both of the planets involved, and when this situation arises they may remain in very close visual proximity for several days or even longer). The quasi-conjunction is reckoned as occurring at the time the distance in right ascension between the two planets is smallest, even though, when declination is taken into account, they may appear closer together shortly before or after this.

Notable conjunctions

Triangular conjunction formed by the Moon, Venus (left) and Jupiter, seen from São Paulo, Brazil, on 1 December 2008.

Moon, Venus and Jupiter formed a smile face :) seen from Eastern Asia

2008

On 1 December 2008, 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.^[2]

2007

A very remarkable planetary/galactic configuration occurred on 23–24 December 2007. 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 was accompanied by the Full Moon (conjunct Mars) at about 2 a.m. on December 24 when a simultaneous Venus square Neptune occurred. It is even more remarkable in that the Pluto/Sun conjunction appears exactly on the December Solstice, just past conjunction with the Galactic Centre.

Link below is the view from Mars toward the Jupiter, Mars, Earth, Mercury, Pluto alignment toward the Galactic Centre on 23 December 2007 which occurs just after the Pluto/Jupiter (Heliocentric) conjunction on 23 November 2007. NASA Solar System Simulator for 23 December 2007

Solar System on 22 December 2007. 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 December 2007.

2002

In late April 2002, a rare great 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 24, 1987, 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 great 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

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

See also

• Astrometry
• Positional astronomy
• Astronomical opposition
• Elongation
• Great conjunction
• Great conjunction#Greatest conjunction
• Syzygy (astronomy)
• Transit of Venus
• Triple conjunction
• Astrological aspects
  • 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)

References

External links

• Occultations of Saturn by Jupiter
• Image of 2001 occultation of Saturn by the Moon
• Planets conjunctions and mutual occultations 1000BC to 3000AD
• Conjunctions of planets with the main asteroids
• Planetary Alignments: Fact or Fiction?