Conjunction astronomy: Encyclopedia - Conjunction astronomy

Conjunction (astronomy)

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 symbol of conjunction is ☌.

Conjunction astronomy - 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.

Conjunction astronomy - 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 closest 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 in front of the sun, this event is called a solar 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 is larger than the farther one, it will completely obscure its smaller companion; this is an occultation. 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, which will generally occur every few years.

Conjunction astronomy - One famous event

It is often believed that the Star of Bethlehem was a triple conjunction between Jupiter and Saturn in the year 6BC. However the angle distance between Jupiter and Saturn was at this event approximately 1 degree, this is twice the diametre of the moon in the sky. Occultations of Saturn by Jupiter did not occur in historic times and will not occur before the year 7541.

Conjunction astronomy - 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 further 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.

Conjunction astronomy - Grand conjunctions

Conjunction astronomy - 2007

A very remarkable planetary/galactic configuration occurs on 23rd and 24 December 2007. The 23/12 configuration — Mars, Earth, Sun, Mercury, Jupiter, Galactic Centre, is shown in the graphic simulation (link) below; it becomes even more remarkable in that it will be joined/triggered by the full moon (conjunct mars) at about 2am 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.

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 23rd Dec 2007

Conjunction astronomy - 2002

In late April of 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 of 2060, except that on that occasion the quintet will be bunched in the east-northeast sky, shortly before dawn.

Conjunction astronomy - 2000

In May of 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.

Conjunction astronomy - 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.

Conjunction astronomy - Conjunctions of planets in right ascension 2005-2020

Conjunction astronomy - 2005

Conjunction astronomy - 2006

Conjunction astronomy - 2007

Conjunction astronomy - 2008

Conjunction astronomy - 2009

Conjunction astronomy - 2010

Conjunction astronomy - 2011

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Conjunction astronomy - 2020

See also

• Astrological aspects
• Astronomical opposition
• Elongation
• Great Conjunction
• Greatest Conjunction
• Transit of Venus
• Triple Conjunction

Adapted from the Wikipedia article "Conjunction astronomy", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki