On December 21, 2020, Griffith Observatory in Los Angeles captured an image of Saturn and Jupiter in the night sky.
This phenomenon has been christened as a ‘Great Conjunction’ by ancient sky watchers who believed that these two were the slowest planets in the sky. Their conjunction was, therefore, a rare occurrence.
Jupiter takes more than a decade to make a full circle in the sky while visiting each zodiacal sign, whereas Saturn takes 29.5 years to go around the sun.
Given these planets apparent slow movement in the night sky to ancient astronomers, a celestial meeting had special significance.
Saturn and Jupiter's Great Conjunction
Even though these conjunctions happen roughly every twenty years, this recent one has special meaning for many. Here are some of the reasons:
Degree of separation
These two planets have been separated during recent conjunctions by about one degree or twice the moon’s diameter. However, on 21st, the separation was only 6arc minutes, a rare and impressive sight.
In simple terms, six arc minutes equals 0.1 degrees or 1/5 of the moon’s apparent diameter. You may be wondering whether this small degree of separation could have made the planets appear to merge into a single bright star, but the answer is no.
The last time the two planets appeared so close in the night sky was on July 16, 1623, almost 400 years ago. The separation was only five arc minutes, which is much closer than the recent occurrence.
However, not everyone saw the occurrence. People living in temperate latitudes such as New York, Paris, and Tokyo didn’t get the chance to watch the conjunction of the two planets due to the sun’s glare.
This limited where on the planet the great conjunction of 1623 was visible, for many it occurred during the day.
Those who got to witness the 1623 alignment were from the tropics near the equatorial regions. On the evening of July 16, 1623, people living in northern South America, Central Africa, and Indonesia were treated to the sight of these two planets in the west-northwest sky coming together.
The last time most of the world’s population had a clear view of these two planets coming close was March 5, 1226, almost 800 years ago. The degree of separation was just two arc minutes, which appeared very close together.
Research has shown that this proximity between the two planets in the night sky happens only once every 300 years.
Star of wonder
Several people have likened the conjunction of December 21, 2020, to the star of Bethlehem. The most popular theories of the Christmas Star draw from the series of conjunction between these two planets in 7BC. Saturn and Jupiter met in May, September, and December of 7BC.
The first conjunction, which happened on May 29, was visible in the East. It is presumed that it started the Magi on their way to Bethlehem from the East.
The Middle conjunction on September 30 may have given them the assurance to continue with their journey, and the last on December 5 happened just as they were about to meet King Herod in Judea, who sent them to Bethlehem to search for the young child.
Such triple conjunctions are often less frequent and occur once every 180 years. The last one happened in 1981, and the next is due to occur in 2239.
This year, Saturn and Jupiter had only one meeting, and given the timing, those who believe that this may have been the Christmas star are correct. It is thought that these two stars will come even closer on December 25, 2874 and appear as one star in the sky.
Sadly it’s highly unlikely any of us alive today will get to witness that particular occurrence, unless science and medicine help us out considerably.