A phenomenon not seen for nearly 800 years will light up the sky next week.
Two of the largest planets – Jupiter and Saturn – in the solar system will come together in “a great conjunction” right in time for Christmas, the U.S. space agency NASA reported. It is also the same day as the winter solstice.
Jupiter and Saturn are, actually separated by more than four times, hundreds of millions of miles, the distance between Earth and the sun. But on the night of the winter solstice, they will be separated in the sky by a distance equal to about one-fifth of a full moon’s diameter, according to Patrick Hartigan, an astronomer from Rice University in Texas.
The cosmic phenomenon, which could have caused such awe and wonder more than 2,000 years ago, is set to take place once again – just four days before Christmas as it happens.
The alignment of Jupiter and Saturn will be visible from anywhere on Earth – though conditions will be best near the equator.
“What has become known popularly as the ‘Christmas Star’ is an especially vibrant planetary conjunction easily visible in the evening sky over the next two weeks as the bright planets Jupiter and Saturn come together, culminating on the night of December 21,” NASA said on its website.
Saturn and Jupiter seen after sunset from Shenandoah National Park in Virginia, December 13, 2020. NASA/Bill Ingalls
The conjunction of the two planets happens about every 20 years, but they are not always the same. This year’s grand conjunction will be the closest observable since 1226, EarthSky reported.
“On the 21st, they will appear so close that a pinkie finger at arm’s length will easily cover both planets in the sky,” NASA said. “The planets will be easy to see with the unaided eye by looking toward the southwest just after sunset.”
“Jupiter will look like a bright star and be easily visible,” NASA said. “Saturn will be slightly fainter and will appear slightly above and to the left of Jupiter until December 21, when Jupiter will overtake it and they will reverse positions in the sky.”
Star of Bethlehem
It is one of the central and most enduring elements of the Christmas story – the sighting of a bright star in the skies guiding the Wise Men to Bethlehem and heralding the birth of Jesus Christ.
The Vatican now believes one explanation for the Star of Bethlehem may have been what is known as a ‘Great Conjunction’ of planets creating an unusually bright light in the sky above the Holy Land.
The closest approach of two planets since 1226 will take place on Monday, December 21, when Jupiter and Saturn come into alignment, creating what astronomers predict will be the marvellous spectacle of an apparently single bright ‘star’.
In 1610, Italian astronomer Galileo Galilei discovered both the four moons of Jupiter — Io, Europa, Ganymede, and Callisto — and the rings of Saturn. Not long after, in 1623, the two planets were spotted aligning for the first time.
In an online lecture on Thursday evening one of the Catholic Church’s most eminent scientists said the latest Great Conjunction may provide us with significant clues to enhance our understanding of the story of the Star of Bethlehem, chronicled in the Gospel of Matthew.
Brother Guy Consolmagno SJ, planetary scientist and Director of the Vatican Observatory, said in a virtual lecture, said: “Every year, people ask us astronomers, what was the star?
“This year is special because one of the more popular explanations for the star is a close conjunction of bright planets and it is going to be visible to anybody with a clear sky.”
Several conjunctions of the planets occurred within 10 years of the chronological point now taken as the beginning of the Christian era and may have been responsible for the phenomenon of the bright star above Bethlehem.
One was a conjunction of Venus and Jupiter in 2BC, which, according to the Encyclopedia Britannica “would have appeared to observers in Babylon to have merged just before setting in the general direction of Bethlehem to the west.”
Another was a conjunction of Jupiter and Saturn in 7BC.
Speaking to the Catholic News Agency before Thursday night’s lecture, Brother Consolmagno said: “Is this really what the Star of Bethlehem was? No one knows for sure what the star was, and until we have a time machine where we can go back and interview Matthew with a video recorder, no one ever will know for sure!”
“The important thing to remember is that the Star of Bethlehem is just a small part of the infancy narrative in Matthew’s Gospel. The point of his story is not the star. It is the baby.”
As Jupiter’s and Saturn’s 12- and 29-year orbits bring them together, they will appear low in the western sky.
When was the last time this happened?
The last great conjunction was in May 2000, but its position in the sky that year meant it was difficult to see. The great conjunction of 1623 was also hard to spot because it appeared close enough to the sun that it would have been lost in the glare.
“You’d have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky.”
How Jupiter and Saturn will appear in a telescope set up in Houston, Texas, on December 21. Patrick Hartigan/Rice University/Adapted from Stellarium graphics
How do I watch the planetary alignment?
Even before Monday observers standing at a vantage point with a clear horizon will be able to see the planets already edging closer together, provided there are clear skies.
NASA said people should look for them low in the south-west in the hour after sunset when “the two giant planets will appear just a tenth of a degree apart – that’s about the thickness of a coin held at arm’s length.”
Viewed through a small telescope, Jupiter and Saturn should appear in the same field of view, along with some of their moons.
For viewers in the U.S., Canada, and Europe, it could be challenging to see this conjunction because of how low it will be on the horizon in the Northern Hemisphere, Hartigan said.
“Viewing conditions are best close to the equator, though no matter where you are there is maybe an hour or so to observe this conjunction before the planets sink into the haze,” he added.
To catch a glimpse, head out around twilight – the hour after sunset – and point your telescope toward the southwestern sky. (Websites like Stellarium can help you orient your telescope.)
“You will need to have a clear southwestern horizon and no low clouds in the distance,” Hartigan said.
He recommends setting up your telescope before it gets dark and bringing binoculars, which could help you spot Jupiter’s four moons too.
If it ends up being cloudy on the night of the solstice, do not worry, Hartigan said. The conjunction is an ongoing event from December 17 to 25, December 21 is just when the two planets will be the closest in the sky.
“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” Henry Throop, a NASA astronomer, said in a press release. “From our vantage point, we’ll be able to be to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”
During the last great conjunction in 2000, Jupiter and Saturn were so close to the sun that the event was difficult to observe. But skywatchers should have a clearer view of the celestial event this time around. The great conjunction will be shining bright shortly after sunset, low in the southwestern sky, as viewed from the Northern hemisphere, NASA said.
Through the entirety of December, skywatchers will easily be able to spot the two planets with the naked eye. You can look up each evening to watch them get closer and closer in the sky — they are so bright, they are even visible from most cities.
Jupiter currently appears brighter than any star in the sky. Saturn is slightly dimmer, but still just as bright as the brightest stars, with a recognizable golden glow.
Saturn will appear slightly above and to the left of Jupiter, and will even look as close to the planet as some of its own moons, visible with binoculars or a telescope. Unlike stars, which twinkle, both planets will hold consistent brightness, easy to find on clear nights.
“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” said Henry Throop, an astronomer in the Planetary Science Division at NASA Headquarters. “From our vantage point, we’ll be able to be to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”
The event is observable from anywhere on Earth, provided the sky is clear. “The further north a viewer is, the less time they will have to catch a glimpse of the conjunction before the planets sink below the horizon,” Hartigan said.
The planets will appear extremely close for about a month, giving skywatchers plenty of time to witness the spectacular alignment throughout the holiday season. The event coincidentally aligns with the December solstice, marking the shortest day of the year in the Northern hemisphere.
“Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits,” said Throop. “The date of the conjunction is determined by the positions of Jupiter, Saturn, and the Earth in their paths around the Sun, while the date of the solstice is determined by the tilt of Earth’s axis. The solstice is the longest night of the year, so this rare coincidence will give people a great chance to go outside and see the solar system.”
To learn more about when and where to look up to see the conjunction, Throop will be live on NASA’s website to answer questions on Thursday afternoon.
Dr Brad Tucker from the Australian National University, who has described the phenomenon as a Christmas Kiss, said observers should look for “a thin crescent moon and two bright objects right next to it.”
It can be photographed with cell phone camera
Jupiter and Saturn’s conjunction “can be photographed easily on DSLR cameras and many cell phone cameras,” NASA said.
The agency suggests using the “night mode” feature on an iPhone, Pixel, or Galaxy to get a stable, long-exposure photo.
“Try to frame the planets with something – the silhouette of a tree, an outdoor landscape, the arch of a building, or even a neon sign,” NASA said.
If a DSLR camera is used, a tripod is recommended to get good long-exposure photos. In the absence of a tripod, set your camera to a shutter speed of less than one-quarter of a second. Also be sure to open your camera’s aperture to its widest setting and use manual focus mode, NASA said.
For people who can’t head outside for the event, the Lowell Observatory in Flagstaff, Arizona, will host a YouTube livestream of views through its telescopes starting at 7 p.m. ET on December 21. In Rome, the Virtual Telescope Project also plans to share live views of the conjunction.
Another conjunction like this will come in 2080
In the last 2,000 years, there were just two times that Jupiter and Saturn came closer in the sky than they will get this year. One was in 1623, but the sun’s glare made it impossible to see. The other was in 1226.
If you miss this upcoming conjunction, another will come in 60 years.
On March 15, 2080, Jupiter and Saturn will look just as close as they do this year. That event will be easier to see, since it will appear higher above the horizon, Hartigan said.
“The major challenge there is you will have to stay alive for another 60 years to see it!” he added.