On Monday, December 21, an incredibly special celestial event occurred. Jupiter and Saturn, two of the biggest planets in our solar, aligned in such a manner that they were only 0.1 degrees apart. Such an event was last observed in Galileo’s time in the 17th century and will now happen in 2080.
Astronomers use the word conjunction to describe meetings of planets and other objects on our sky’s dome. They use the term great conjunction to describe the meetings of Jupiter and Saturn, which are the two biggest worlds in our solar system. Though the two planets will appear spectacularly close together on the sky’s dome now, Jupiter and Saturn are actually 456 million miles (734,000 million km) apart. Saturn is nearly twice as far away as Jupiter.
Jupiter-Saturn conjunctions happen every 20 years; the last one was in the year 2000. But these conjunctions aren’t all created equal. The 2020 great conjunction of Jupiter and Saturn will be the closest since 1623 and the closest observable since 1226! 2020’s extra-close Jupiter-Saturn conjunction won’t be matched again until the Jupiter-Saturn conjunction of March 15, 2080.
At the 2000 great conjunction, 20 years ago, Jupiter and Saturn were near the sun in our sky and difficult to observe. We’re due for a more observable great conjunction. Jupiter and Saturn are up every evening now – not far from the sunset glare – easily visible and exceedingly noticeable as two bright objects near each other. Plus, in the days prior to the conjunction (last week), the young moon appeared appearing in the evening sky, pointing the way to the planets.
In November – during the period when the moon swept past Jupiter and Saturn (about November 16 to November 21) – the two gas giant planets were some 3 degrees apart.
Over the time between November 21 and the day of the conjunction itself, December 21, Jupiter will travel about 6 degrees and Saturn 3 degrees on the sky’s dome. That movement will mean that Jupiter bridges the 3-degree gap between itself and Saturn.
Dr Henry Throop, astronomer in the Planetary Science Division at NASA Headquarters, has revealed why this conjunction has attracted so much attention.
He told Express.co.uk: “It’s been nearly 400 years since the planets passed this close to each other in the sky, and nearly 800 years since the alignment of Saturn and Jupiter occurred at night, as it will for 2020, allowing nearly everyone around the world to witness this ‘great conjunction’.