December 21 marks the winter solstice in the Northern Hemisphere. However, what is going to make it extra special is the occurrence of a rare celestial event dubbed as ‘The Great Conjunction’ between Jupiter and Saturn that is going to be witnessed on the longest night of 2020.
Two of the solar system’s biggest planets—Jupiter and Saturn will align their positions to form a conjunction—nearly overlapping themselves to form a “double planet”, a phenomenon that has not occurred since the 17th century.
What is ‘The Great Conjunction’?
The Great Conjunction is an occasional astronomic event when the two planets—Jupiter and Saturn—appear closest together in the sky. On Monday, Jupiter and Saturn will be very close to each other—a tenth-of-a-degree apart. The last time they were this close and visible, was in 1226 AD. The two planets were this close in 1623 as well but likely not visible due to their proximity to the Sun.
Jupiter and Saturn regularly pass each other, as often as once every 20 years, but what makes this year’s conjunction special is that it is for the first time in nearly 400 years that the two planets will be this close to one another and 800 years since the phenomenon occurred at night.
The conjunction is popularly known as the ‘Christmas Star’ or the ‘Star of Bethlehem’, which, according to the Bible, was the star that guided the three wise men to baby Jesus.
The distance between the two planets would remain the same but the angle of viewing it from Earth would give an impression that the two planets would be very close to each other, only 0.1 degrees apart.
It is to be noted that despite appearing just 0.1 degrees apart, the two planets will be 456 million miles apart. Meanwhile, the distance between Earth and Jupiter is 550 million miles.
According to Space.com, “Jupiter and Saturn are in conjunction when they have the same right ascension or celestial longitude. This is what is referred to as a ‘Great Conjunction’, signifying the rarity of the union because unlike conjunctions with the other bright planets, these two don’t get close as often.”
The next such super close pairing of the two giant planets won’t happen again until the Jupiter-Saturn conjunction of 15 March 2080.
How and when to view ‘The Great Conjunction’?
The “great conjunction” also coincides with the winter solstice, the shortest day (December 21) in the year as the sun reaches a point where it appears to shine farthest to the south of the equator over the Tropic of Capricorn.
The rare celestial event will be visible shortly after the sunset today, between 6:30 PM and 7:30 PM in the southwestern sky. Saturn will be smaller, fainter than Jupiter on the upper right. Though the phenomenon would be visible to the naked eye, binoculars and telescopes will be needed to differentiate between the two planets.