Jupiter and Saturn are converging for a rare “Great Conjunction” on the day of the winter solstice – December 21st

The “Great Conjunction” of December 21, 2020 will feature Jupiter and Saturn so close together that they will appear to most as one very bright star which some are already dubbing the ”Christmas-star”. Credit: Getty Images

By Paul Dorian

Overview

You may have already noticed two close together bright objects in the sunset sky in recent weeks which happen to be the giant gas planets of Jupiter and Saturn. These two planets are actually converging for an even closer encounter in terms of their appearance to us here on Earth – the likes of which haven’t been seen in many, many centuries. Jupiter and Saturn currently appear about 2 degrees apart and they will actually look only 0.1 degrees apart by the time we get to the winter solstice on December 21st – the day of the “Great Conjunction” of 2020.

Jupiter and Saturn will appear extremely close together on December 21st just after sunset in the low southwestern sky. [“Sky map” credit spaceweather.com]

Details

Jupiter and Saturn conjunctions are the rarest of bright-planet conjunctions due to their slow orbits around the sun. Saturn takes nearly 30 years to complete its circle around the sun whereas Jupiter takes nearly 12 years. So just about every 20 years, Jupiter catches up to Saturn as viewed from Earth causing what is referred to by astronomers as a “great conjunction”. Why every 20 years? Each year, Saturn completes about 12 degrees of its orbit around the sun, whereas Jupiter completes approximately 30 degrees. So in one year, Jupiter closes the gap to Saturn by about 18 degrees. In a period of 20 years, Jupiter gains 360 degrees on Saturn (18 x 20 = 360 degrees), meaning lapping Saturn once every 20 years.

This particular Jupiter/Saturn “great conjunction” is extremely rare because of how close the two planets will look to one another and how easy it will be to see. Often, the glare of the sun makes their convergence difficult or even impossible to see from here on Earth, but this year is very special because the conjunction happens comfortably away from the sun.  Here are the dates of the “great conjunctions” from 2000 to 2100:

  • May 28, 2000
  • December 21, 2020
  • October 31, 2040
  • April 7, 2060
  • March 15, 2080
  • September 18, 2100

Jupiter and Saturn already appear close together in the sunset sky and they are about to get even closer from our vantage point here on Earth.  The last time these two gas giants have appeared this close together was in the year 1623 during Galileo’s times, but the sun’s glare that year very likely obscured the pair of planets to sky watchers on Earth. In fact, the last time the two giant gas planets appeared so close together and were so easy to see was during medieval times in the year 1226. While Jupiter and Saturn appear quite close together to us in the sunset sky, they are actually about 450 million miles apart from each other. They will appear to get closer and closer each night during the next couple of weeks and – as an added bonus – the crescent Moon will join the planets on the 16th and 17th of December making for a beautiful sight assuming good viewing conditions. 

By the time we get to the winter solstice on December 21, Jupiter and Saturn will appear only 0.1 degrees apart, which is just 1/5 of a full moon diameter. In fact, they will appear so close together that Saturn will actually look to us as close to Jupiter as some of its own moons.  The two planets may appear as a “double planet” to some depending on local viewing conditions or as one very bright star to others in the low southwest sky shortly after sunset. Some are already referring to this great conjunction of Jupiter and Saturn as the “Christmas Star” because of the timing just a few days before Christmas. Note- some Biblical scholars believe the “Star of Bethlehem” was a triple conjunction made up of the following:

  • Jupiter (known as the king planet)
  • Venus (the brightest planet in our solar system)
  • The star Regulus (known as the kingly star) in the constellation Leo.
A look at Jupiter’s position in the sky relative to some of its largest moons which actually appear in a linear fashion. In January 1610, Italian astronomer Galileo Galilei discovered four of Jupiter’s moons — now called Io, Europa, Ganymede and Callisto. There are now thought to be as many as 79 moons of Jupiter with Europa being about the same size as Earth’s moon.

Jupiter and Saturn should be visible within the same field-of-view on December 21st whether using binoculars or a small “backyard” telescope along with four of Jupiter’s largest moons spread out in a straight line. Beyond December 21, Jupiter and Saturn will move away from each other rather quickly in terms of appearance to us here on Earth and this trend will continue for the next ten years before they start to converge again during the 2030s.  This will set up the next “Great Conjunction” of the year 2040; however, that one will not be as brilliant as this one. In fact, the two planets won’t appear this close again until the year 2080 and in that late 21st century close encounter, Jupiter will completely cover Saturn which is an extremely rare event and won’t happen again until the year 7541.

Final Comments

Make sure to mark your calendars specifically for December 21st to view this once-in-a-lifetime celestial event as this opportunity will be just a one-day affair.Just one day before and one day after, the planets will appear noticeably farther apart from each other and nowhere near as striking as on December 21st – hopefully skies will cooperate on the first day of astronomical winter. The best viewing on December 21st will be from about 30 minutes to an hour after sunset in the low southwestern sky until the time the two planets set (~8:23 PM ET).

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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Video discussion on “The Great Conjunction of December 21, 2020”.

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Lewis Buckingham
December 12, 2020 2:39 am

Whatis the chance of seeing this in the Southern Hemisphere, Australia?

KAT
Reply to  Lewis Buckingham
December 12, 2020 3:40 am

Both planets are already visible in the early evening sky. Look on the ecliptic just after the sun sets.

Shanghai Dan
Reply to  Lewis Buckingham
December 12, 2020 8:58 am

Southern Hemisphere?

invert the polarity, carry the 1, subtract back pi to the e power…

I think possible?

Jeff Alberts
Reply to  Shanghai Dan
December 12, 2020 10:15 am

Stand on your head. Much easier.

Pat from kerbob
Reply to  Jeff Alberts
December 12, 2020 2:12 pm

On my one visit to Oz in 2004 I was initially baffled looking at the stars which I fixed by facing south and then leaning way back, then the stars looked right

But after too much Bundaberg rum I would end up laying on the ground

Fun time had by all

Annie
Reply to  Jeff Alberts
December 14, 2020 5:04 am

When we first came to Australia I was really upset at seeing my favourite constellation, Orion, upside down! He looks very odd standing on his head with his sword pointing upwards. I was very pleased to see the Magellanic Clouds for the first time in my life though, while camping in Glendambo in SA. The sky was incredible, so clear. So different from light-infested Melbourne where it was also difficult to see Halley’s Comet properly.
Missed the Geminids this morning, too asleep. Years ago we came and camped on the slope of the large dam here (giving head support). Saw a corker of a meteor. It was freezing cold so ended up back in the house with hot coffee and brandy!

Annie
Reply to  Lewis Buckingham
December 14, 2020 4:51 am

Yes, in Victoria, Aus. I looked out c. 10pm and saw them close together roughly to the SW. I’m keeping my fingers crossed for clear sky on the 21st, if they are not behind a nearby hill by the 21st.

Under The Bridge
December 12, 2020 3:30 am

Be sure to see this rare celestial event that will never happen again because of climate change!

fred250
Reply to  Under The Bridge
December 12, 2020 1:12 pm

We won’t be able to see it through the CO2 for. !

Just ask Greta.

Wade
December 12, 2020 5:15 am

Regarding the article’s comments about the star of Bethlehem, there is a lot of misconceptions. First, we were never told the number of the astrologers/magi/wise men. Most people assume it was three because they gave three gifts.

Second, the star led the magi to Herod first. When Herod heard that these men were looking for the “king of the Jews”, he was disturbed and asked the astrologers to find him and report back. The star then led the astrologers to a house, not a manger, where Jesus was no longer a baby. Because of a divine warning, the astrologers didn’t report back to Herod, so he had all the young boys under 2 years old killed. But it was too late. Joseph used the expensive gifts he received to finance a trip to Egypt, out of Herod’s reach. Whatever you believe about the star, it was not from God as depicted in nativity scenes. Why would God send men to someone who wanted to kill his son first?

Jeff Alberts
Reply to  Wade
December 12, 2020 10:17 am

“Why would God send men to someone who wanted to kill his son first?”

Indeed. This also led to the supposed killing of many innocent children, as you point out.

AndyHce
Reply to  Jeff Alberts
December 12, 2020 6:31 pm

Sacrificing children has been a part of various religions.

Greg
Reply to  Wade
December 12, 2020 11:45 am

Accepting the possibility of the existence of an omniscient deity, it is an act of extreme naivety and arrogance to assume you can apply you puny human intellect to decide what God would or would not do and imagine you could understand his motives and infer conclusions of what did or did not happen from that.

Aphan
Reply to  Greg
December 12, 2020 12:55 pm

Exactly.

gringojay
Reply to  Wade
December 12, 2020 12:33 pm

King Herod died in 4 B.C. Then too, Mathew & Luke give different ages for how old young Jesus was when the Magi visited.

Where were the Facebook/Twitter/SouthernPovertyLawCenter “fact checkers” when we really could have used them?

PCman999
Reply to  gringojay
December 12, 2020 6:18 pm

We only have 1 reference for Herod’s year of death, based on the eclipse reference in Josephus’ work, but he’s not perfect and has contradicted himself in his various works. I seen other researchers come up with dates closer to AD1. On the other hand, the AD convention was created much later, when the empire was falling apart and counting the years by installation of counsuls was losing it’s effectiveness.

Aaron D.
Reply to  gringojay
December 12, 2020 7:25 pm

Luke’s gospel makes no reference to the Magi so there is no difference in this regard between Luke’s and Matthew’s accounts.

Aphan
Reply to  Wade
December 12, 2020 12:48 pm

Your logic is flawed.

First, God did not send the magi to Herod. The magi were following a prophecy that the Messiah would be born in Bethlehem of Judah. Herod was in Jerusalem, not Bethlehem. Herod learned from the Magi the exact time of the new “star’s” appearance and told them to find the child and return to report.

Supposing an all knowing God, the “star” itself could have been an ordinary, natural but rare phenomenon, that God knew would occur at the same time as the birth of Christ, thus the prophecies included it as a sign. That all knowing God would ALSO know Herod was both lazy AND stupid and would not have the wise men followed, nor go to Bethlehem himself. That God would just plan to warn the Magi to not return home through Jerusalem.

Keep in mind that the birth of Christ occurred BEFORE the calendar and current holidays were established. Saturnalia was a pagan holiday in December, not a Christian holiday, and totally unrelated to the birth of Jesus. Most historians place his birth in the Spring, during lambing season. How long it took the Magi to travel to Jerusalem is unknown. How long the star-phenomenon remained visible is also unknown.

Pat from kerbob
Reply to  Aphan
December 12, 2020 2:15 pm

Bethlehem and Jerusalem almost the same thing
Just across a deep gorge from southern edge of the Temple Mount
Surprisingly close

Aaron D.
Reply to  Pat from kerbob
December 12, 2020 7:40 pm

Bethlehem is 5 miles south of Jerusalem. You’re probably thinking of Bethphage.

Reply to  Wade
December 12, 2020 1:02 pm

Wade
According to one study I came across, the “wise men” could have been a diplomatic delegation from the neighboring Parthian empire, custodians of the prophecies and teachings of the prophet Daniel some centuries earlier, and from whom the Zoroastrian religion would emerge. Such delegations would not be on camel but horseback, and there would not be 3, more like 70. There would be an armed horse-cavalry detachment with them. This would explain a comment in the gospel account of the visit of the Magi that is rarely noticed: “Herod at this was deeply agitated, and all Jerusalem with him. (Matt 2:3)

All Jerusalem would not be perturbed by a handful of oriental visitors among the hundreds coming and going every day.

ak in vt
Reply to  Wade
December 12, 2020 4:40 pm

The purpose of the telling of this incident in the Bible is to take the readers of the time (in the 50-60 A.D. decade) back to something they either remembered or their parents, elders in their community had told them about a long while ago. It could have been written as follows (working backwards):

“Do you remember the time when Herod had the innocent children slaughtered and when the princes and magi from the East came with their huge entourage to see the newborn king? This was when the Christ child was about 2 years old, and when he was brought to Egypt by his parents to escape the wrath of Herod. And there was weeping and wailing in Ramah; Rachel weeping for her children.”

One needs to look at the point of the narrative — in this case, giving known facts that would place the time when these other events (the birth, the slaughter of the innocents, the move to Egypt to fulfill other prophecy, etc…) occurred.

Regarding to the time He was born (see Aphan’s comments below), it is also thought that He was born during the feast of Tabernacles as the literal translation in John states “He tabernacled among us” rather than “He dwelt among us.” As well, Elijah is/was expected to return at Passover (Jews still keep an emty seat and place setting for him at Passover Seder) which is six months before Tabernacles and John the Baptist (Elijah returned) was born six months before the Christ child!

All interesting. And, thank you Paul Dorian and WUWT for posting this info on this exciting meteorological and astronomical event. I heard about it over a month ago and you have given me more detail. We will be watching, hopefully with clear skies.

Regards in Christ

AK in VT

Ge0ld0re
Reply to  ak in vt
December 12, 2020 9:58 pm

I was interested in the relation of planet conjunctions to the time of the birth of Christ. Of course, we must assume the Bethlehem star to have been a significant one to make this project have significance, and the star may instead have had significance from other aspects than brightness. But assuming it was inordinately bright could we not search for a conjunction in the seasons of Spring or Autumn depending upon whether it was Tabernacles or Passover? (Obviously, no shepherd in his right mind would “keep watch over his flocks by night” in the dead of winter, so I would look to Spring or Fall (or Summer) conjunctions.] There are many guesses on years and months of His birth, anywhere from BC10 to CE10 and I would like to know of possible conjunctions in the Springs or Falls of those years. Also if there is a star supposed to be a star of Moses and its position relative Pisces and Virgo during those same time periods. This has been a fun discussion; I’ve enjoyed all contributors.

Vuk
December 12, 2020 5:22 am

What we can see from our rocky planet may be very interesting, but matters very little. What matters is how the three gas magnetic giants Sun, Jupiter & Saturn connect to each other with their magnetic fields and the electric currents.
http://www.vukcevic.co.uk/J-S-angle.htm

Leif Svalgaard
Reply to  Vuk
December 12, 2020 9:23 am

What matters is how the three gas magnetic giants Sun, Jupiter & Saturn connect to each other with their magnetic fields
The Sun’s magnetic field [via the supersonic solar wind] connects with all planets with a magnetic field all the time, but that has no effect on the Sun as the wind is supersonic, that is moves away from the Sun much faster than any magnetic [or electric] effects can move towards the Sun. So, it matters not.

Vuk
Reply to  Leif Svalgaard
December 12, 2020 10:26 am

Hi doc, thanks for your observation
Capacity of the Earth magnetosphere is too small to have significant effect, but in case of Jupiter and Saturn feedback effect looks like might be there.
Quote:
“Contrary to previous ideas about Saturn’s magnetosphere being unlike its terrestrial counterpart, these findings reveal that Saturn at times behaves and interacts with the Sun in much the same way as Earth.” Jamie Jasinski, UCL Space and Climate Physics PhD graduate now based at the University of Michigan, and lead author of the new paper published in Geophysical Research Letters.
This not only shows that magnetic reconnection occurs at Saturn but also that Saturn’s magnetic field can at times interact with the Sun ….
The analysis was completed using a particle spectrometer built at UCL and a magnetometer built at Imperial College, both of which are onboard NASA’s Cassini spacecraft.
https://www.ucl.ac.uk/mathematical-physical-sciences/news/2016/jul/magnetic-rope-observed-first-time-between-saturn-and-sun
Keep safe.

Leif Svalgaard
Reply to  Vuk
December 12, 2020 1:43 pm

This not only shows that magnetic reconnection occurs at Saturn but also that Saturn’s magnetic field can at times interact with the Sun ….
Sure, all planets’ magnetic fields are connected to the sun and the sun interact with those planets all the time, but the important thing is that the interaction is one way: sun to planet.
There is no interaction the other way: planet to sun. So, the conjunction does not matter as far as the magnetic fields are concerned as the connection is there all the time. Further more, the conjunction is that seen from the earth, and has nothing to do with the interaction between the sun and the planets. I have lost count of how many times I have explained that to you, so here is yet one more. Hopefully [?] that will be the last. If not, …

noaaprogrammer
Reply to  Leif Svalgaard
December 12, 2020 6:17 pm

I thought that magnetic fields propagated at the speed of light. I also thought that magnetic fields were an intrinsic part of the son and some of its planets. If this is the case, why wouldn’t interactions be mutual? — albeit very very insignificant on the part of a planet’s effect on the sun.

Leif Svalgaard
Reply to  Leif Svalgaard
December 12, 2020 7:18 pm

I thought that magnetic fields propagated at the speed of light
In an electric conductor they propagate with the Alfven speed which is generally much lower than the speed of light. In the solar wind near the Earth the Alfven speed is about 50 km/sec. The issue is that a static magnetic field does not ‘propagate’. A change of the magnetic field propagates in a plasma [which is a near perfect conductor] as a wave with the Alfven speed. Here is a longer [and more technical] explanation
http://www-solar.mcs.st-and.ac.uk/~bernie/mhdwaves.pdf

noaaprogrammer
Reply to  Leif Svalgaard
December 12, 2020 9:00 pm

Thanks Leif for the link. I was conflating magnetohydrodynamic waves with static magnetic fields.

Gordon A. Dressler
Reply to  Vuk
December 12, 2020 12:49 pm

Well, the Jupiter-Saturn “Great Conjunction” event coming up in a little over one week from now should serve to dispel any claimed gravitational or electromagnetic coupling-related “forcings” on solar activity, such as increasing the number of sunspots or CMEs.

Just scroll down this webpage and look on the far right side until you come to the solar image under the “Solar Images & Data Page” header. There you will see a near-perfect smooth-complexioned solar disk image, with no evidence of being disturbed by the current alignment of Jupiter and Saturn.

And in reality this conjunction has essentially existed for the past few weeks and will likewise essentially exist for several weeks following the day of closest alignment (Jupiter and Saturn appearing to be about 0.1 degree of arc apart as seen from Earth) . . . the relative angular movement of Saturn relative to Jupiter being pretty slow.

And then there is this article: https://www.southerncaliforniaweatherforce.com/2020/07/08/great-conjunction-of-jupiter-and-saturday-in-december-2020-to-test-earthquake-and-volcanic-theory/ which shows the conjunction as viewed from Earth also represents a relatively close (albeit larger spaced) alignment as viewed from the Sun . . . in astronomy, the word “conjunction” is typically used to mean close planetary (or other astronomical objects) as seen from Earth.

M__ S__
December 12, 2020 5:31 am

So. The Pagans were right all along.

Randle Dewees
December 12, 2020 5:40 am

Will have to roll my 8 inch refractor out I suppose. Ro might be pretty good right after sunset

Michael
Reply to  Randle Dewees
December 15, 2020 8:18 pm

Wow, a 8″ refractor, (not a reflector?) now that is quite a fine and rare beast of a telescope. I have a basic 10″ reflector. Almost big enough… I’m pretty sure a 18″ might suffice. Yes I’m afflicted w aperture fever, caused by the orionebulaM42 virus, rather expensive to successfully treat, and it can recur. Nonetheless, the view of the conjunction in a nice wide-angle high-mag eyepiece, for days prior and after, will be great. Would be sweet to see the perfect conjunction/occultation of 2080, but my telomeres are laughing hysterically at that notion. Happy stargazing!

Dodgy Geezer
December 12, 2020 6:48 am

I could never get very excited about conjunctions.

They were much more significant for the mediaeval (and earlier) mindset, since their world view assumed a real impact on earth to two Gods or guiding influences meeting in the Heavens. In our age this has diminished to a requirement not to slew your telescope so much when viewing each planet…..

Vuk
Reply to  Dodgy Geezer
December 12, 2020 8:29 am

Romans lacked imagination and simply appropriated the old Greek gods.
Cronus (Saturn) “Father Time” was the father of Zeus (Jupiter) the god of the sky and thunder.
For more easy narrative google ‘ Planet Myths: The Story Behind Saturn (or Jupiter, or Mars etc) – Jessica Davidson

Randle Dewees
Reply to  Dodgy Geezer
December 12, 2020 8:17 pm

My main reservation is it’s going to be cold. But having both planets in one high power field is interesting – I imagine Jupiter will kind of wash out Saturn’s moons… I think that aspect will be worth seeing.

Might have The Planets playing in the background. I won’t be around to view it but having Saturn occulted by Jupiter, that I would love to see.

December 12, 2020 7:41 am

“Great Conjunction” good term for an interesting article.
However, the alignment is also described as a syzygy.
In a not widely circulated paper Michael Mann is fretful that when as many as five planets get in line, all of the refrigerator magnets in the world will fall off.

Jeff Alberts
Reply to  Bob Hoye
December 12, 2020 10:20 am

“In a not widely circulated paper Michael Mann is fretful that when as many as five planets get in line, all of the refrigerator magnets in the world will fall off.”

“Dogs and cats living together…”

Pat from kerbob
Reply to  Bob Hoye
December 12, 2020 2:19 pm

😀😀😀😀😀😍

Reply to  Bob Hoye
December 13, 2020 11:13 am

@Bob Hoye December 12, 2020 at 7:41 am

You made me laugh so hard!!!! Thankyou.

Greg
December 12, 2020 11:56 am

Thanks for the heads up. I noted earlier this evening that J and S were getting quite close and wondered how much nearer they were likely to get. You’ve just saved me wasting time trying to find some site which actually tells me.

December 12, 2020 1:04 pm

Weather forecast for 21 Dec here in Belgium: rain!
Maybe next time …

TonyG
December 13, 2020 11:49 am

The timing of this, on a solstice, is apparently fairly rare. I didn’t do the work, but I saw someone report that the last time it was on a solstice was around 250 BC. Not that important, I suppose, but interesting, at least to me.

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