On December 21, 2020, Jupiter and Saturn appeared closer together in Earth’s sky than they had in nearly 400 years, separated by just a tenth of a degree. This event, known as a great conjunction, happens roughly every 20 years as the two largest planets in the solar system line up from our perspective, but the 2020 edition was extraordinary because of just how tight that gap was. Dubbed the “Christmas Star” by the media, the conjunction landed on the winter solstice and became one of the most widely watched astronomical events in recent memory.
What Made the 2020 Conjunction Unusually Close
Great conjunctions are not rare in themselves. Jupiter orbits the Sun about every 12 years, Saturn about every 29, and the geometry works out so that Jupiter “laps” Saturn roughly once every two decades. What made 2020 remarkable was the angular separation. The two planets closed to about 6.1 arcminutes apart at their nearest, which is roughly one-fifth the apparent diameter of a full Moon. To the unaided eye under decent conditions, they almost merged into a single bright point of light, and many casual observers genuinely struggled to split them without binoculars.
The previous conjunction this close occurred in July 1623, but that one was essentially unobservable because it happened so near the Sun in the sky that the glare swallowed both planets. You have to go back to March 1226 to find a Jupiter-Saturn conjunction that was both this tight and practically visible to people on the ground. That roughly 800-year gap between easily watchable super-close conjunctions is what drove the excitement. Typical great conjunctions place the two planets about a degree or two apart, close enough to share a binocular field of view but clearly separate to the naked eye. The 2020 event was an order of magnitude tighter.
What You Were Actually Seeing
It is worth pausing on what a conjunction is and is not. Jupiter and Saturn did not physically approach each other in December 2020. They were still separated by roughly 450 million miles of empty space. A conjunction is a line-of-sight alignment: Earth, Jupiter, and Saturn happened to fall along nearly the same sightline when viewed from our planet. Think of two cars on a distant highway that appear to overlap from where you stand even though one is a mile ahead of the other. The alignment is real, but the proximity is an illusion of perspective.
Jupiter, orbiting closer to the Sun than Saturn, was the brighter of the pair, shining at roughly magnitude −2.0. Saturn was dimmer, around magnitude +0.6. Through a telescope at moderate magnification, both planets and their moons could fit inside a single eyepiece field of view at the same time, something that almost never happens with the naked-eye planets. Saturn’s rings and Jupiter’s Galilean moons were visible together in the same frame, and astrophotographers captured stunning images showing both planetary disks simultaneously. For many amateur astronomers, that shared-eyepiece view was the real highlight rather than the naked-eye dot.
Timing, Visibility, and the Winter Solstice Coincidence
The conjunction peaked on December 21, which also happened to be the winter solstice in the Northern Hemisphere. That coincidence fueled the “Christmas Star” branding in the popular press, though the timing was purely geometric and had nothing to do with the solstice mechanism. The two planets had been visibly converging for weeks leading up to the event. By early December they were already strikingly close, and patient observers could watch them inch together night after night.
The viewing window was short. Both planets sat low in the southwestern sky after sunset, setting within a couple of hours of the Sun. People in mid-northern latitudes had perhaps 60 to 90 minutes of useful darkness before the pair sank below the horizon. Southern Hemisphere observers had a somewhat better geometry, with the planets higher above the horizon at equivalent times after sunset. Cloud cover and local geography were the main enemies. If you had trees, buildings, or hills to your southwest, you could miss the event entirely even on a clear night.
For people who did catch it, the speed of the alignment was part of the fun. By December 25, just four nights later, the gap between the planets had already widened noticeably. The super-close window lasted only a handful of evenings around the 21st, which added urgency and made the event feel fleeting in a way that slower astronomical phenomena like comet apparitions do not.
Why Great Conjunctions Follow a 20-Year Cycle
Jupiter takes about 11.86 Earth years to complete one orbit, and Saturn takes about 29.46 years. After Jupiter completes one full orbit, Saturn has moved roughly 40 percent of the way around its own orbit, so Jupiter needs a little extra time to catch up. The math works out to a synodic period of about 19.86 years between successive conjunctions. In practice, the interval can range from around 18 to 21 years because of the eccentricities and inclinations of both orbits, but two decades is a reliable rule of thumb.
There is a secondary pattern that takes longer to appreciate. Successive conjunctions do not happen in the same part of the sky. Each one shifts roughly 117 degrees eastward along the ecliptic relative to the background stars. After three consecutive conjunctions, which takes about 60 years, the positions form a rough triangle on the sky. This triangular pattern slowly rotates over centuries, and it takes about 800 years for the conjunction points to cycle all the way through the zodiac. This longer rhythm is what determines whether a given conjunction will be especially close or relatively wide: the orbital geometries that produce a sub-arcminute pairing only align at certain points in the cycle.
The “Christmas Star” and the Star of Bethlehem Debate
The media’s use of “Christmas Star” for the 2020 event drew on a long-running astronomical discussion about what, if anything, the Star of Bethlehem described in the Gospel of Matthew might have been. The astronomer Johannes Kepler, observing a Jupiter-Saturn conjunction in 1603, proposed that a similar conjunction in 7 BCE could explain the biblical account. That idea has persisted in various forms for over four centuries. A recent interdisciplinary analysis revisits Kepler’s hypothesis by examining the kinematics and observational circumstances of the 7 BCE conjunction, in which Jupiter and Saturn came close together three times over the course of several months due to retrograde motion.1arXiv. Testing Kepler’s Hypothesis on the Star of Bethlehem: A Kinematic and Astronomical Analysis of the 7 BCE Jupiter-Saturn Conjunction
The triple conjunction of 7 BCE is a different beast from a single close pass like the one in 2020. In a triple conjunction, Earth’s own orbital motion causes the two planets to appear to separate and re-converge over several months, producing three distinct close approaches. To ancient sky-watchers, this would have been a prolonged and attention-grabbing spectacle in a way that a single-night conjunction is not. Whether it explains a specific biblical narrative remains a matter of scholarly and theological debate, but Kepler’s core insight, that great conjunctions are predictable and calculable events, was a milestone in shifting astronomical thinking away from mystical interpretation.
Great Conjunctions in Medieval and Pre-Modern Thought
Long before telescopes existed, great conjunctions were treated as events of enormous significance. The doctrine of great conjunctions, first developed by the Arab astrologer Albumasar in his work on religions and dynasties, framed the Jupiter-Saturn cycle as a driver of major earthly events: the rise and fall of civilizations, the emergence of new religions and prophets, plagues, floods, and famines.2Quaestio. Yearbook of the History of Metaphysics. Astrology and Politics: The Theory of Great Conjunctions in Albert the Great This was a form of general astrology, meaning it concerned the fate of nations and civilizations rather than individual horoscopes, and it had serious political weight in the medieval Islamic and Christian worlds.
European scholars like Albert the Great and Roger Bacon engaged with the conjunction doctrine seriously, treating it as a framework for understanding historical periodization. The roughly 20-year cycle was thought to mark shifts in political fortune; the 60-year triangular return was linked to larger generational changes; and the roughly 800-year full rotation through the zodiac was associated with civilizational upheaval. None of this has any scientific validity, but it mattered historically because it meant that astronomers who could calculate conjunction dates held political influence. Predicting the next great conjunction was a form of political forecasting, and court astronomers across the Islamic world and medieval Europe were valued partly for this reason.
The 2020 conjunction inevitably revived some of this thinking in popular culture, with social media posts attributing transformative energy to the event. The astronomical community generally ignored this, but the cultural continuity is genuinely interesting. The same planetary alignment that medieval astrologers used to predict the collapse of dynasties was being discussed on Twitter as a harbinger of a new “Age of Aquarius.” The planets, of course, are indifferent to the symbolism we project onto their orbits.
What the Conjunction Looked Like Through a Telescope
For anyone with even a modest backyard telescope, the 2020 conjunction offered a view that no living person had experienced before. At around 60x to 100x magnification, both planets appeared as resolved disks in the same eyepiece field. Jupiter’s equatorial bands were visible alongside Saturn’s rings, with the Galilean moons (Io, Europa, Ganymede, and Callisto) strung out to either side of Jupiter like tiny pearls. Saturn’s largest moon, Titan, was also visible as a faint dot nearby.
The scene was unusual enough that experienced observers described it as almost surreal. Normally, switching from Jupiter to Saturn requires re-pointing the telescope and refocusing, which reinforces the mental sense that these are separate objects in separate parts of the sky. Seeing them together, close enough that Saturn’s rings and Jupiter’s cloud bands were visible simultaneously, collapsed that mental separation in a way that photographs do not fully capture. Many astronomy outreach groups held socially distanced viewing events despite the COVID-19 pandemic, and for many first-time telescope users, the conjunction was their introduction to planetary observation.
When Will It Happen Again
Great conjunctions are not something you need to wait centuries for. The next one occurs on November 4, 2040, when Jupiter and Saturn will meet again in the sky. However, that conjunction will be wider, with the planets separated by about 1.1 degrees, which is roughly 11 times the gap of 2020. Perfectly watchable and interesting, but the two planets will be clearly distinct to the naked eye.
The next conjunction rivaling the closeness of 2020 is much further off. The pair will not come within a comparable separation until March 15, 2080. That event will place Jupiter and Saturn about 6 arcminutes apart, nearly matching the 2020 configuration. Whether it will be as visually striking depends on where the conjunction falls relative to the Sun. A close conjunction that happens in broad daylight or deep in twilight is academically interesting but practically invisible. The 2020 event benefited from being far enough from the Sun to be seen in a reasonably dark sky, and that fortunate geometry is part of what made it special.
For observers willing to settle for a merely excellent conjunction rather than a once-in-a-lifetime one, the 20-year cadence means that anyone alive in 2020 will likely see at least one or two more great conjunctions in their lifetime. The 2040 event will be the next opportunity, followed by another around 2060. Each will offer a chance to see the solar system’s two gas giants sharing the same patch of sky, even if they do not merge into a single dazzling dot the way they did in December 2020.
The Pandemic Backdrop
It is impossible to discuss the 2020 great conjunction without acknowledging the context in which people experienced it. December 2020 was deep in the COVID-19 pandemic, with vaccines just beginning to roll out in a handful of countries but daily death tolls still climbing in many parts of the world. Public gatherings were restricted, travel was limited, and for many people the conjunction was one of the few shared communal experiences available that winter.
Social media played a disproportionate role in amplifying the event. Hashtags like #GreatConjunction and #ChristmasStar trended globally, and millions of people stepped outside to look southwest after sunset who might not otherwise have paid attention to a planetary alignment. Astronomy educators noted that engagement with the event far exceeded what they would have expected based on the conjunction’s objective brightness or rarity. The pandemic, paradoxically, created conditions where people were hungry for something collectively awe-inspiring that did not require a crowd, and a celestial event visible from every backyard on Earth fit that need perfectly.
Observatories and planetariums that were closed to in-person visitors ran livestreams instead, some attracting hundreds of thousands of viewers. The conjunction became a case study in how digital outreach can reach broader audiences than physical events. Whether that momentum carries forward to the 2040 conjunction remains to be seen, but the 2020 event demonstrated that public appetite for naked-eye astronomy is far larger than the astronomy community sometimes assumes.
Photographing a Planetary Conjunction
One reason the 2020 conjunction left such a visual footprint online is that it was relatively easy to photograph with consumer equipment. Unlike deep-sky objects that require long exposures and tracking mounts, Jupiter and Saturn are bright enough to capture with a smartphone held up to a telescope eyepiece, a technique called afocal photography. Even standalone smartphone shots from a tripod could resolve the two planets as a tight pair against the twilight sky, though resolving any detail on the planetary disks required at least a small telescope.
For those using DSLRs or mirrorless cameras, a telephoto lens in the 200mm to 600mm range was enough to clearly separate the two planets and show color differences: Jupiter’s warm cream tones against Saturn’s paler yellow. Stacking multiple short exposures helped reduce atmospheric shimmer and brought out the Galilean moons as distinct dots. Astrophotographers who used telescopes with dedicated planetary cameras produced images showing both planets in sharp detail, with Jupiter’s Great Red Spot and Saturn’s Cassini Division visible in the same frame. Those images, widely shared online, became some of the most iconic astronomical photographs of the decade.