by John Church

As we are all aware, there will be a close conjunction of Jupiter and Saturn in the evening sky of Monday Dec. 21, which coincidentally is the same day as the winter solstice.  Jupiter passes Saturn once in about every 20 years as seen from Earth, but in most cases they are not nearly so close together in the sky as they will be this time.  

About 30 years ago I became interested in such conjunctions as close as or closer than 6 arc minutes, and I researched them with the aid of advanced ephemeris technology.  (The upcoming one will be 6.1 arc minutes at closest approach, but I included it as being in the foreseeable future.)  I wrote up my results and sent an article to Sky & Telescope for consideration in the Astronomical Computing feature moderated by Roger Sinnott. A corollary was my finding that Jupiter hadn’t actually occulted Saturn as far back as 4000 BC, and won’t do so until at least the year 2800 AD. 

Because the ecliptic passes near Regulus (Alpha Leonis, often called the “Royal Star”), I was especially intrigued by close conjunctions that have occurred in its immediate neighborhood, i.e. within 10 degrees.  Such events might have had significance for contemporary astrologers.  The events of 1794-3 BC struck me as having been possibly associated with the rise of Hammurabi, the “lawgiver king” of Babylonia (reigned ca. 1792-1750 BC).  The fine 940 BC triple conjunction near Regulus might have had some connection with King Solomon (reigned ca. 970-931 BC); the lion has long been associated with Israel, and both the five-and six-pointed stars have been called the Seal of Solomon. The coming event is not near Regulus, but is still quite interesting as it will be the closest such conjunction readily visible since the year 1226. 

The following table is abridged from my original data.  My article appeared in the March 1991 issue of Sky & Telescope, pages 305 to 307.  Those who may be interested in the entire article may be able to make copies for their own private use from back issues kept in one of the branch libraries of Princeton University.  In the past, these branches have been open to the public free of charge; this may again be the case after the Coronavirus issue has passed.  Unfortunately I have no photocopies available.

Notes to the table:  All dates before 2020 AD are in the Julian rather than the Gregorian calendar.  A negative sign under “Separation” indicates that Saturn was or will be south of Jupiter at the time of closest approach.  Celestial longitudes are measured along the ecliptic eastward from the vernal equinox of date.  “T” means that the event is part of a “triple conjunction” of the two planets; “R” means the event was near Regulus, and “M” means that there was also a “massing” of other planets in the vicinity.   This was  the case with the 26 BC event (not a particularly close one), but included because of this as well as nearness to Regulus.  Events closer to the sun than 15 degrees were omitted. Please see the original of the article for full details and accompanying illustrations.