The two largest planets in the solar system, Jupiter and Saturn, will appear closer to each other in the night sky than at any point in the past 800 years, astronomers say.
Both gas giants, they have been gradually getting closer to one another since the start of summer and will appear almost as double planet system on December 21.
The phenomenon, known as a conjunction, can be viewed anywhere on Earth but from the UK they will be very low on the horizon – seen just after sunset.
At their closest position, the two worlds will appear less than a full moon’s width apart – just after sunset on the winter solstice and up until about Christmas Day.
German astronomer, Johannes Kepler, wrote in 1614 that he believed the ‘star of Bethlehem’ in the biblical story of the three wise men could have been a rare triple conduction of Jupiter, Saturn and Venus.
While Venus won’t be visible as part of the 2020 conjunction, it will still be an impressive astronomical site, best viewed on the equator but seen worldwide.
Jupiter and Saturn will appear closer to each other in the night sky on December 21 than they have been for nearly 800 years, astronomers have said. Pictured, how the night sky in the south west will appear on the evening of the winter solstice
On December 21 Saturn and Jupiter will appear low on the horizon just after sunset in the south west – they will be less than a full Moon width apart – appearing almost as one object
If you have a telescope and look towards Jupiter and Saturn on December 21 they will appear further apart than they do from Earth but you will still see the larger moons and the two gas giants within the same field of view
Those in London and New York will see the planets close to the horizon (at around 5.3° and 7.5°, respectively around an hour after the sun sets.
‘Alignments between these two planets are rather rare, occurring once every 20 years or so,’ said astronomer Patrick Hartigan of Rice University of Houston, Texas.
‘But this conjunction is exceptionally rare because of how close the planets will appear to one another,’ he explained.
‘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.’
German astronomer, Johannes Kepler, wrote in 1614 that he believed the ‘star of Bethlehem’ in the biblical story of the three wise men could have been a rare triple conduction of Jupiter, Saturn and Venus
The next such conjunction of the two bodies after that will not be until sometime after the year 2400.
‘On the evening of closest approach on Dec 21 they will look like a double planet, separated by only 1/5th the diameter of the full moon,’ Professor Hartigan added.
‘For most telescope viewers, each planet and several of their largest moons will be visible in the same field of view that evening.’
The next time that Jupiter and Saturn will seem as close in the sky will not be until March 15, 2080 — at which they will be higher in the sky and visible for longer.
Twitter users have been sharing images of the night sky showing Jupiter and Saturn (seen in the centre between the trees) as they get closer together
While Kepler thought a conjunction of Jupiter, Saturn and Venus was behind the ‘star of Bethlehem’ story in the bible, others believed it may have been another astronomical event such as a large comet in the sky.
Professor Hartigan said the planetary duo will appear low in the western sky around sunset — and should be bright enough to be viewed in the twilight sky.
In reality the two planets will still be millions of miles apart – Jupiter is about 5AU from the Earth (one AU is the distance of the Earth from the Sun) and Saturn is 10AU away from the Earth – but they appear together due to differences in their orbit.
When Jupiter and Saturn (pictured as bright lights here) come together, they will be visible at twilight in the south western sky
Having been ‘nearing’ each other since the summer, the giant planets will come to appear less than a full moon’s width apart just after sunset on the winter solstice, pictured
The celestial sight should — local weather permitting — be visible from anywhere on the Earth, experts said, although the best views are to be had near the equator. ‘On the evening of closest approach on Dec 21 they will look like a double planet, separated by only 1/5th the diameter of the full moon,’ said US astronomer Patrick Hartigan added. ‘For most telescope viewers, each planet and several of their largest moons will be visible in the same field of view that evening’
The two planets will gradually become closer and closer throughout November and December until they appear as a single object on December 21 – before moving apart after Christmas
‘The further north a viewer is, the less time they’ll have to catch a glimpse of the conjunction before the planets sink below the horizon,’ Professor Hartigan explained.
‘By the time skies are fully dark in Houston, for example, the conjunction will be just 9 degrees above the horizon,’ he added.
‘Viewing that would be manageable if the weather cooperates and you have an unobstructed view to the southwest.’
If you have a telescope and look up towards the conjunction on December 21 you will not only see Jupiter and Saturn, but some of their largest moons in the same field of view, according to astronomers.
Users have been sharing images of Jupiter and Saturn – that appear as bright stars – as they come closer together on the run up to their conjunction on December 21
THE STAR OF BETHLEHEM: INSPIRED THE THREE WISE MEN TO BABY JESUS IN BIBLE STORIES
The Star of Bethlehem, or the Christmas Star, is said to have inspired the three wise men from the East to visit the baby Jesus in bible stories.
It appears in the nativity story of the Gospel of Matthew, where they are said to have asked King Herod of Judea ‘where is he who has been born King of the Jews’ For we have seen His star in the East and have come to worship Him.’
It is said the star led them to Jesus’ home town where they worship him and give him gifts of gold frankincense and myrrh.
The gospel describes the visitors as ‘Magi’ which is usually translated as ‘wide men’ but can also be used to mean astronomer/astrologer.
Astronomers have made several attempts to calculate what this star may have been – whether it was a celestial event or pious fiction.
Famed German astronomer, Johannes Kepler, wrote in 1614 that he believed the ‘star of Bethlehem’ in the biblical story of the three wise men could have been a rare triple conduction of Jupiter, Saturn and Venus.
This would create a very bright point of light in the sky that would only appear for a few days. A similar conjunction is due to happen Christmas 2020.
Other theories are a supernova explosion reasonably close – that could appear like a very very bright sky for a relatively short period, or even a comet.
Chinese and Korean stargazers have written about a bright object that may have been a comet or supernova around 5 BC seen for more than 70 days.
Ancient astronomers have written of comets ‘hanging over’ specific cities – just as the Star of Bethlehem is said to have ‘stood over’ the place where Jesus was born – the town of Bethlehem.