This Christmas period, there will be more than just Santa to look for in the night sky. On 21 December, Jupiter and Saturn will appear to touch for the first time since 1226.
This alignment is referred to as the ‘Great Conjunction’ and from anywhere on Earth the planets will seem so close that they appear to form a “double planet”. The planets will actually still be separated by a vast distance, with Jupiter at 530.68 million miles and Saturn at 0.98 billion miles away from Earth at the time this article was written, but to us they will seem so close that they cannot be separated by the human eye. The alignment is clearer the closer to the equator you are, but if it’s a clear night it should be visible in the Sheffield sky to the south-west.
On average, conjunctions occur between Jupiter and Saturn every 20 years, which is why this planetary conjunction is referred to as a Great Conjunction. A conjunction is when two or more celestial objects appear to be close together, with the event occurring between planets, stars, and the moon on a regular basis. However, they are usually only in alignment, rather than appearing as a “double planet” as they will on 21 December. With this conjunction of Jupiter and Saturn occurring on the winter solstice, the longest night of the year in the Northern Hemisphere and a day of many celebrations globally, it brings us a little magic as 2020 draws to an end. This won’t be the first time we have witnessed a conjunction around Christmas, and it’s theorised that the famous Star of Bethlehem was actually a conjunction between Venus and Jupiter.
A list of other Great Conjunctions spanning 3,000 years has been created by Patrick Hartigan from Rice University. He states that a closer Jupiter-Saturn conjunction occurred in 1623, but probably wasn’t seen by many at the time due to its placement. With the telescope having only been invented 14 years earlier, by Italian astronomer Galileo Galilei.
In 2015, a Venus and Jupiter conjunction occurred in June where viewers could “cover both of the planets with just their pinky held at arm’s length”, and things will be even closer this time around with the planets only 0.1 degrees apart. The planets will be closest on the winter solstice, but we can still look forward to an impressive sight on the following nights. Small telescopes will even be able to see a range of both Jupiter’s and Saturn’s moons.
Unlike the conjunction of 1623, the conjunction of 1226 was clearly visible to onlookers without any astronomical equipment. It should be even easier to see this year, as with apps such as Google Sky maps and Stellarium, anyone with a phone can track the planets today.
The last time many were able to witness this phenomenon, Henry III was King of England and the Magna Carta had been signed just 9 years earlier. With the next chance to see this alignment is after 2400, keep an eye out for this rare sight – you probably won’t be around for the next one!
