The two massive gas giant planets of the solar system pair with a rare connection between Jupiter and Saturn at dusk on December 21.
A unique view adorns the twilight sky worldwide and closes 2020 with one of the best astronomical events of the year.
Every year dozens of planetary conjunctions grace our skies as two planets appear to pair from our earthly point of view. Many are quick affairs as fast moving inner worlds such as Mercury and Venus orbit the sky and visit the moon, planets and stars along the ecliptic.
It is more unusual to spy on a pairing of the two slowest moving outer planets with the naked eye, Jupiter and Saturn. This is exactly what will happen next Monday when Jupiter meets Saturn on December 21st. At ~ 6:00 p.m. UT (1:00 p.m. EST), 30 degrees east of the sun, the two worlds appear to be only 6.1 arc minutes (’) apart.
Looking west on the evening of December 21, 2020. Photo credit: Stellarium.
Although the two largest planets in the solar system orbit each other once per generation (approximately every 20 years), this connection is particularly close: In fact, it will only be exceeded on March 15, 2080 (6.1 ’). You'll have to go all the way back to July 16, 1623 to find a closer one (5.2 inches apart), though that particular conjunction was much lower in the sky and much more difficult to see, only 13 degrees from the Sun. . The last highly visible pairing of Jupiter and Saturn that year was on the morning of March 5, 1226 AD.
Jupiter and Saturn over Elliott Bay from Queen Anne Hill, Seattle @KSeattleWeather @ScottSKOMO @NWSSeattle @Astroguyz pic.twitter.com/V2Cd3hNjqF
– Columbia (@ whitesky60) December 13, 2020
Though the timing of its closest approximation favors lengths that focus on Europe and Africa, you can see the two grow closer together night after night around the world this weekend this weekend. In fact, Jupiter and Saturn remain less than a degree apart (slightly close enough to hide behind your pinky finger at arm's length) through December 30th, and closer than 30 '(the Angular diameter of a full moon) 25.
"Puny Gas Giant (s) …" The author hides Jupiter and Saturn behind a thumb. Photo credit: Dave Dickinson
The two planets appear to be almost touching on the evening of the 21st, when in fact the two gas giants are 883 million kilometers (548.7 million miles) apart. Jupiter shines with a strength of -2, while Saturn with a strength of +0.6 is only seven times weaker. The couple missed the wafer-thin, growing crescent moon by just three degrees on Wednesday evening, December 16. (Photo op!)
Make sure you increase the magnification as you will have the rare opportunity to bring both of the solar system's gas giants into the same field of view. You are viewing over 90% of the planetary mass of the entire solar system in one convenient view. Jupiter has a diameter of 33 arc seconds (") on the night of conjunction, while Saturn has a diameter of 36" (with rings) from tip to tip. Be sure to take a look at the respective entourage of the moons as they slide past each other in the sky.
When moons collide … Saturn, Jupiter and moons from the evening of December 12th. Picture credits and copyright: Ralph Smyth. Used with permission.
Views from space
If you look back from near Saturn, you can see that Jupiter slides just 7 inches past Earth, both only three degrees from the Sun.
The 17th astronomer Johannes Kepler attached great importance to the conjunction of Jupiter and Saturn. Kepler was the last great astronomer to also partially join the archaic practice of astrology, and he extensively studied what he termed "great conjunctions" or repeated conjunctive patterns of Jupiter and Saturn returning to the same astrological house every 60 years.
Kepler's "trine" of major conjunctions. From De Stella Nova, 1606. Public Domain.
These "trines" or triads of large conjunctions had a major impact on Kepler's thinking, leading him to believe that the star of Bethlehem was closely related to Jupiter and Saturn in 7 BC. in Pisces the Pisces, a sign that has long been associated with Judaism.
The dawn in 7 BC Image credit: Stellarium
This year's conjunction takes place on the border of the modern astronomical constellations of Sagittarius and Capricorn. Expect the annual discussion on “What was the star of Bethlehem?” As the conjunction falls just a few days before Christmas. to come back to the fore … while biblical and historical references to the actual event are so sparse, we will likely never know for sure.
Look into the distant future
Can Jupiter ever occult Saturn? Well, we've looked at conjunctions worth 20,000 years (which we do for fun) and found 58 close (less than 10 & # 39; separated) conjunctions of Jupiter and Saturn over 200 centuries, only 11 of which were in 2000 from 1000 AD to 3000 AD … But only 5 that are closer than the conjunction in 2020.
Close (less than 10 & # 39; separated) connections of Jupiter versus Saturn over a period of 2000 years from AD 1000 to 3000. Photo credit: Dave Dickinson
A particularly fascinating event can occur (mark your calendars) on June 21, 7541 AD, when Jupiter can actually occult Saturn (pass before it). This is sure to be a bizarre spectacle as the moons of the two intertwine and Jupiter wears the rings of Saturn! We say "May" because the exact position of the planets is subject to tiny gravitational perturbations over extremely long periods of time, and these tiny effects result in little uncertainty when we look over tens of thousands of planets.
There is not much scientific value behind the conjunction next Monday evening, but the spectacle offers a wonderful opportunity to show the two worlds on the eyepiece while we reflect on the clockwork universe and how it offers us such rare views of time and space.
Main image: Closer: Jupiter vs. Saturn on December 8, 2020. Photo credits and copyright: Tom Wildoner / Dark Side Observatory. Used with permission.