Dec 21 Copy
The Great Conjunction of 2020
"O Star of Wonder, Star of Night,
Star with Royal Beauty bright,
Guide us to Thy perfect Light."
~ We Three Kings, John Henry Hopkins Jr., 1857
Tonight marks a unique observational opportunity for stargazers in the long dark night of the winter solstice. Jupiter and Saturn will be so close today that they will appear to form a "double planet" or a new "bright star" visible in the night sky. Such a spectacular great conjunction, as this planetary alignment has come to be known, hasn't occurred in nearly 800 years. The 2020 great conjunction is especially rare — the planets haven't been this close together in nearly 400 years, and haven't been observable this close together at night since medieval times, in 1226.
Although the subject of much dispute, some historical and biblical researchers have theorized that the Star of Bethlehem, chronicled in the Book of Matthew, may be explained by the appearance of a visiting comet, sudden visible remnants of a supernova, or even by a conjunction of planets such as tonight's! In the year 7 B.C., Jupiter and Saturn had three conjunctions in the same constellation, Pisces. Four years later, in the summer of 3 B.C., Jupiter and Venus met in an event that would have looked much like tonight's planetary entanglement. Ancient astrologers, astronomers, and historians, may well have taken note and could have retroactively ascribed meaning to such events in the timeframe ascribed to the birth of Christ.
Tonight's "Christmas Star" is best observed between 30-24 minutes after sunset! 🪐 🔥 🔭
A great conjunction is a conjunction of the planets Jupiter and Saturn, when the two planets appear closest together in the sky. Great conjunctions, named "great" for being the rarest and one of the brightest and closest on average of the conjunctions between "naked eye" planets (i.e. not counting the rarer conjunctions involving the ice giants as they were too dim to be discovered until after the invention of the telescope), occur approximately every 20 years when Jupiter "overtakes" Saturn in its orbit.
Astronomers have recorded and documented these events since the 13th century.
Some of the more noted conjunctions are the following:
When studying the great conjunction of 1603, Johannes Kepler thought that the Star of Bethlehem might have been the occurrence of a great conjunction. He calculated that a triple conjunction of Jupiter and Saturn occurred in 7 BC (−6 using astronomical year numbering). A triple conjunction is a conjunction of Jupiter and Saturn at or near their opposition to the Sun. In this scenario, Jupiter and Saturn will occupy the same right ascension on three occasions or same ecliptic longitude on three occasions depending on which definition of "conjunction" one uses (this is due to apparent retrograde motion and happens within months). The most recent triple conjunction occurred in 1980 and 1981 while the next will be in 2238 and 2239.
The astronomers from the Cracow Academy (Jan Muscenius, Stanisław Jakobejusz, Nicolaus Schadeck, Petrus Probosczowicze, and others) observed the great conjunction of 1563 to compare Alfonsine tables (based on a geocentric model) with the Prutenic Tables (based on Copernican heliocentrism). In the Prutenic Tables the astronomers found Jupiter and Saturn so close to each other that Jupiter covered Saturn (actual angular separation was 6.8 minutes on 25 August 1563). The Alfonsine tables suggested that the conjunction should be observed on another day but on the day indicated by the Alfonsine tables the angular separation was a full 141 minutes. The Cracow professors suggested following the more accurate Copernican predictions and between 1578 and 1580 Copernican heliocentrism was lectured on three times by Valentin Fontani.
The great conjunction of 2020 was the closest since 1623 and eighth closest of the first three millennia AD, with a minimum separation between the two planets of 6.1 arcminutes. This great conjunction was also the most easily visible close conjunction since 1226 (as the previous close conjunctions in 1563 and 1623 were closer to the Sun and therefore more difficult to see). It occurred seven weeks after the heliocentric conjunction, when Jupiter and Saturn shared the same heliocentric longitude.
This conjunction attracted considerable media attention, with news sources calling it the "Christmas Star" due to its proximity to Christmas.
Designed by Aljean of Vancouver in 1972, the original inspiration for this fashion tartan is not known.
For more on the possible astronomical origins of the Star of Bethlehem, click Jupiter and Saturn!