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.

More generally, in particular in the 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 normally not 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.

However, if the two celestial bodies attain the same declination at the time of a conjunction at right ascension (or the same ecliptical largitude at a conjunction in ecliptical longitude), the one closest to the Earth will pass in front of the other. In such a case an occultation tooks place, or if the moon passes in front of the sun a solar eclipse, if Mercury passes in front of the sun a transit of Mercury or if Venus passes in front of the sun a transit of Venus. Occultations, especially such in which the eclipsing body is not the sun or the moon are very rarely. More frequent, however, 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 in the case of a lunar eclipse). Solar eclipses are globally considered not rare events (every year occur at least two), but for a certain location, especially total or annular solar eclipses are rarely.

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.

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.

Contents

1 Grand Conjunctions

1.1 2007
1.2 2002
1.3 2000
1.4 1987

2 Conjunctions in Right Ascension in 2005-2007

3 See also

4 Weblinks

Grand Conjunctions

2007

A very remarkable planetary/galactic configuration occurs on 23rd and 24th 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 24th when a simultaneous Venus square Neptune occurs. It's 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 23rd of Dec 2007 which occurs just after the Pluto/Jupiter (Heliocentric) conjunction on 23rd Nov 2007. NASA Solar System Simulator for 23rd Dec 2007 (http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=5&vbody=4&month=12&day=23&century=20&decade=0&year=7&hour=00&minute=0&fovmul=1&rfov=30&bfov=30&porbs=1&brite=1)

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.

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.

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.

Conjunctions in Right Ascension in 2005-2007

Date	Time UTC	Planet	Angle distance	Planet	Elongation to sun
January 14th, 2005	00:40:51	Mercury	21' south of	Venus	18,5° West
February 8th, 2005	01:29:22	Mercury	2°04' south of	Neptune	4,2° West
February 14th, 2005	19:15:10	Venus	58' south of	Neptune	10,7° West
February 20th, 2005	00:46:34	Mercury	1°00' south of	Uranus	4,9° Ost
March 4th, 2005	03:31:36	Venus	41' south of	Uranus	6,6° West
March 28th, 2005	22:31:53	Mercury	4°49' north of	Venus	1,5° West
April 13th, 2005	00:26:23	Mars	1°15' south of	Neptune	66,0° West
May 14th, 2005	20:24:10	Mars	1°11' south of	Uranus	73,8° West
June 25th, 2005	21:22:52	Venus	1°18' north of	Saturn	22,8° East
June 26th, 2005	06:13:43	Mercury	1°25' north of	Saturn	22,5° East
June 27th, 2005	20:18:55	Mercury	5' south of	Venus	23,3° East
July 7th, 2005	08:21:22	Mercury	1°38' south of	Venus	25,8° East
September 2nd, 2005	12:05:52	Venus	1°22' south of	Jupiter	38,7° East
October 6th, 2005	07:01:37	Mercury	1°28' south of	Jupiter	12,6° East
January 17th, 2006	02:23:03	Mercury	7°53'south of	Venus	6,5° West
February 1st, 2006	12:13:51	Mercury	1°57' north of	Neptune	4,5° East
February 14th, 2006	15:40:57	Mercury	2' north of	Uranus	14,1° East
March 26th, 2006	21:02:41	Venus	1°52' north of	Neptune	46,5° West
April 18th, 2006	12:27:31	Venus	19' north of	Uranus	45,0° West
June 17th, 2006	22:50:40	Mars	35' north of	Saturn	42,0° East
August 20th, 2006	22:40:10	Mercury	31' north of	Saturn	11,2° West
August 26th, 2006	23:09:47	Venus	4' north of	Saturn	16,3° West
September 15th, 2006	20:32:28	Mercury	10' south of	Mars	12,1° East
October 24th, 2006	19:44:11	Venus	43' north of	Mars	0,6° West
October 25th, 2006	21:42:16	Mercury	3°56' south of	Jupiter	21,2° East
October 28th, 2006	16:32:15	Mercury	3°43' south of	Jupiter	19,1° East
November 7th, 2006	13:36:58	Mercury	1°14' south of	Venus	2,8° East
November 11th, 2006	17:51:38	Mercury	39' north of	Mars	6,2° West
November 15th, 2006	22:52:15	Venus	27' south of	Jupiter	4,8° East
December 9th, 2006	20:17:18	Mercury	1°02' north of	Mars	15,1° West
December 11th, 2006	23:34:02	Mars	49' south of	Jupiter	15,7° West
January 18th, 2007	18:10:50	Venus	1°25' south of	Neptune	20,1° Ost
January 26th, 2007	06:46:07	Mercury	1°28' south of	Neptune	12,7° Ost
February 7th, 2007	13:13:57	Venus	44' south of	Uranus	24,6° Ost
March 25th, 2007	07:23:59	Mars	1°00' south of	Neptune	43,2° West
April 1st, 2007	06:59:14	Mercury	1°37' south of	Uranus	25,0° West
April 28th, 2007	18:57:38	Mars	44' south of	Uranus	50,6° West
July 2nd, 2007	00:44:38	Venus	46' south of	Saturn	42,6° Ost
August 9th, 2007	08:46:28	Venus	8°29' south of	Saturn	10,6° Ost
August 15th, 2007	22:59:23	Mercury	10°04' north of	Venus	1,8° Ost
August 18th, 2007	11:30:22	Mercury	30' north of	Saturn	3,2° Ost
October 15th, 2007	14:05:43	Venus	2°56' south of	Saturn	45,8° West
December 20th, 2007	21:46:21	Mercury	1°48' south of	Jupiter	1,9° Ost