Conjunction (astronomy)
In astronomy, a conjunction occurs when two astronomical objects or spacecraft appear to be close to each other in the sky.
A conjunction is an apparent phenomenon caused by the observer's perspective: the two objects involved are not actually close to one another in space.
At the time of conjunction – it does not matter if in right ascension or in ecliptic longitude – the involved planets are close together upon the celestial sphere.
For example, if the Moon passes into the shadow of Earth and disappears from view, this event is called a lunar eclipse.
When the nearer object appears larger than the farther one, it will completely obscure its smaller companion; this is called an occultation.
A conjunction, as a phenomenon of perspective, is an event that involves two astronomical bodies seen by an observer on the Earth.
Times and details depend only very slightly on the observer's location on the Earth's surface, with the differences being greatest for conjunctions involving the Moon because of its relative closeness, but even for the Moon the time of a conjunction never differs by more than a few hours.
Quintuple conjunctions involve Mercury, because it moves rapidly east and west of the sun, in a synodic cycle just 116 days in length.
An example will occur in 2048, when Venus, moving eastward behind the Sun, encounters Mercury five times (February 16, March 16, May 27, August 13, and September 5).
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 quasiconjunction 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.
The following table gives these average intervals, between corresponding conjunctions, in Julian years of 365.25 days, for combinations of the nine traditional planets.
On February 27, 1953, BC, Mercury, Venus, Mars and Saturn formed a group with an angular diameter of 26.45 arc minutes.
On July 5th, 1054 a supernova brighter than Venus appeared in the eastern part of constellation Taurus in the proximity of the waning crescent moon.
The exact geocentric conjunction in right ascension took place at 07:58 UTC on this day with an angular separation of 3 degrees.
Saturn passed Kepler's Supernova on December 12th, 1604 33 arc minutes southly, which was however unobservable as the elongation to the sun was just 3.1 degrees.
On January 20th, 1605 Venus passed Kepler's Supernova 29 arc minutes northwards at an elongation of 43.1 degrees to the sun.
In early December 1899 the Sun and the naked-eye planets appeared to lie within a band 35 degrees wide along the ecliptic as seen from the Earth.
As a consequence, over the period 1–4 December 1899, the Moon reached conjunction with, in order, Jupiter, Uranus, the Sun, Mercury, Mars, Saturn and Venus.
Conjunctions took place between the Moon and, in turn, Mars, Saturn, the Sun, Mercury, Venus and Jupiter.
[11] In May 2000, in a very rare event, several planets lay in the vicinity of the Sun in the sky as seen from the Earth, and a series of conjunctions took place.
A series of conjunctions between the Moon and, in order, Saturn, Mars and Venus took place on 14 May, although it was not possible to observe all these in darkness from any single location on the Earth.
On December 21, Jupiter and Saturn appeared at their closest separation in the sky since 1623, in an event known as a great conjunction.
Planetoid Pallas passed Sirius, the brightest star in the night sky, on October 9 to the south at a distance of 8.5 arcminutes (source: Astrolutz 2022, ISBN 978-3-7534-7124-2).
