Great conjunction 2020: what time can you see Jupiter and Saturn align on the winter solstice from the UK?
People across the world will be able to view Jupiter and Saturn as they closely align in the night sky on 21 December.
Nearly 400 years have gone by since the two planets were last this close to each other in the sky, and 2020 marks the first time in nearly 800 years since the alignment has occurred at night, meaning the rare celestial event can be seen by everyone the world over.
The celestial event is known as the great conjunction by astronomers and has also been nicknamed a Christmas Star or Star of Bethlehem.
What is the Great Conjunction?
It’s a rare phenomenon which sees Jupiter and Saturn appear to align in the sky.
The two Gas Giants are rarely seen this close, with experts predicting they will be separated by less than the apparent diameter of the moon.
Though they will look aligned the two planets will be hundreds of millions of miles apart.
The Great Conjunction has also taken the nickname of Christmas Star and Star of Bethlehem due to the time of the year this alignment occurs.
In the Bible, the Christmas Star was what the wise men used as a guide to help them find the birthplace of Jesus Christ.
What the actual bright light was has been debated for many years with one possible explanation being a rare conjunction of multiple planets.
When was the last Great Conjunction?
The last time the planets appeared to be this close was almost 400 hundred years ago on 16 July 1623, when according to NASA, the two planets travelled together across the sky before Jupiter caught up to and passed Saturn.
Henry Throop, astronomer in the Planetary Science Division at NASA Headquarters in Washington, said: “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.
“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.”
Although the planets appear to pass each other regularly – roughly every 20 years - the reason this conjunction is rare is because it’s the closest they’ve appeared in 400 years, and the first time in 800 years they’ve appeared so close in the night sky.
Where will I be able to see it?
The Christmas Star will be visible from Earth, with the help of a clear night’s sky.
The two planets moved into closer alignment from Thursday 17 December for roughly a week, with the closest point being Monday 21 December.
Stargazers can expect to see the phenomenon low in the western sky shortly after sunset, meaning people in the UK should be on the lookout from 3.54pm.
According to NASA, on 21 December the planets will appear so close that a pinkie finger at arm’s length will cover both planets in the sky.
It is bright enough to be seen without the use of telescopes or binoculars, yet astronomers say several of the planets’ satellites will be visible with viewing aides.
How far away are Saturn and Jupiter from Earth?
Jupiter's distance from Earth is constantly changing due to the different orbits of the two planets. It is 365 million miles away at its closest point and 601 million miles away at its furthest.
It's a similar story with Saturn's orbit, which has its own course and doesn't run parallel with Earth's, meaning the distance varies.
Even at its closest point Saturn is still 746 million miles away and just over a billion miles away from Earth at its furthest point.
There are 403.3 million miles between Jupiter and Saturn.
How big are Saturn and Jupiter?
Jupiter, the fifth planet from the Sun, is the largest in the Solar System. It is 11 times wider than Earth, with a radius of 43,440 miles.
Saturn is sixth in line in the order of planets from the Sun and is the second largest. It is nine times the width of Earth, with a radius of 36,183 miles.
Earth has a radius of 3,960 miles. The radius is a straight line from the centre to the circumference of a circle.