The Great Conjunction of 2020

On December 21st, coincidentally the Solstice (Winter in the Northern and Summer in the Southern Hemisphere), the two giants of our solar system, Jupiter and Saturn, violated physical distancing restrictions and came within 7 arc minutes (1 degree has 60 arc minutes) of each other in the evening sky. This conjunction was apparent, meaning, they appear to be close to each other due to the perspective from Earth. In reality, Jupiter and Saturn (the fifth planet and sixth planet from the Sun, respectively), were still more than 733 million kilometers (456 million miles) apart. Observers from Earth could see Jupiter and Saturn move closer and closer together in their careful celestial dance in the post-dusk time throughout December.

Image 1: Solar System Viewer Sky Live for December 21st, 2020

A conjunction between Jupiter and Saturn happens every 20 years due to their respective orbital speeds and orbital periods around the Sun. A conjunction this close happens, statistically, about every 400 years and then, it depends on the position of the planets’ conjunction in relation to the Sun to be observable ⏤ too close to our home star and they disappear in the glare of the Sun’s luminosity. 400 years ago, this Great Conjunction was glared out which means the last time any human could see this type of apparition was 800 years ago. For December 21st, Stellarium gave you a good indication of where to look for this celestial smooch.

Image 2: Stellarium "The Great Conjunction" (~7 PM MST)

A zoom-in shows not just the lineup of the planets’ moon but also that their angular distance is a lot less than 30 arc minutes, less than half a degree, which means that they come closer to each other than the width of a Full Moon.

Image 3: Stellarium Zoom-in for "The Great Conjunction" (~7 PM MST)

All you needed was a good view of the Western horizon and clear skies, which can be a problem since hobby astronomers’ sacrifices of live chicken to the weather gods have been severely hampered by the pandemic restrictions on outdoor altar offerings. Speaking of gods, Jupiter is the Roman name for the Greek god Zeus and Saturn the Roman name for Cronos, Zeus’ father, who lost his rulership in the War of the Titans after a decade long battle according Greek mythology.

If you wanted to image this planetary event, a 300mm lens or longer would have been a good choice. Even better to depict the details of Jupiter and his atmospheric bands would have been a small telescope with a connected digital camera. My setup was simple, using the RedCat 51 (250mm prime lens) and my Sony A7Riii:

Image 4: Setup for The Great Conjunction

Image 5: The Great Conjunction; 2.5 Seconds; ISO 2000; 250mm, f/4.9 RedCat 51

Image 6: Cropped with Annotations

Alas, the Great Conjunction proved to be a great reminder that celestial phenomena happen with recurring predictability, regardless of the state of human affairs. See you in 400 years.

For more info on the Great Conjunction:

NASAWeb 2020, “The Great Conjunction of Jupiter and Saturn”, (link)

Etz, D.E. 2020, “Conjunctions of Jupiter and Saturn”, JRASC, 94, 174, (link)

Rice University, 2020, "Jupiter-Saturn Conjunction Series from 0 CE to 3000 CE" (link)