The Absolute Cosmos: The Jupiter-Saturn Great Conjunction 21 Dec 2020
In astronomy, conjunction occurs when two astronomical objects/spacecrafts appear close to each other in our sky. Great conjunction is when two gas giants (Jupiter and Saturn) of our solar system meet.
By now you must have heard/read about the Jupiter-Saturn Great Conjunction due to occur on 21st December 2020. This conjunction of gas giants is called “Great” because it happens less often than other planetary conjunctions.
The Great Conjunction happens when Jupiter and Saturn appears closest together in the sky in every 19.859 years, but this year’s event is ultra rare as two planets have not come this close since 16 July 1623- that was almost four centuries ago. And they won’t be this close again until 15 March 2080.
In general, 2020 has been a treat for sky gazers with few comets passing inner solar system, meteor showers happening, solar/lunar eclipses occuring and now Great conjunction of gas giants forming a ‘Christmas Star’ on the winter solstice.
On 21st December, two planets can be viewed as a single bright star in the night sky without any vision enhancements- that’s right, no need of telescope.
Great conjunction takes place because of our perspective from Earth,…….. as viewed from Earth two planets appear to be occupying the same spot in the sky but in reality the planets are millions of kilometres from each other, even at their closest points.
As Jupiter and Saturn revolves around the Sun, sometimes they turn out forming a straight line with Earth. This is when we look the planets along that line, they appear pretty close in a Great Conjunction.
The two planets are appearing close for sometime now and will keep getting closer till Monday, December 21-the day of closest conjunction-when they will be separated by just 0.1 degree. After that they will appear slowly moving away from each other.
Jupiter appears brighter than any other star, while Saturn has distinct golden colour. The ringed planet Saturn appears just to the east of Jupiter on the sky’s dome.
2020 Great Conjunction will be visible from everywhere on Earth, but near the equator conditions will be the best.
Jupiter takes 11.9 Earth years to complete one revolution around Sun, while Saturn’s orbital period is 29.5 Earth years. This time difference to complete an orbit is why Great Conjunctions happen only every 20 years.
Last great conjunction occurred twenty years ago in 2000, but it was pretty difficult to observe as Jupiter and Saturn were near the Sun in our sky.
The Christmas Star or the Star of Bethlehem
This rare event is also sometimes referred as Christmas Star because it is believed that the biblical tale of the Bethlehem star could have been a planetary conjunction, although Venus and Jupiter were closest some two thousand years ago not Jupiter and Saturn.
The Great Conjunction has also been nicknamed Christmas Star and Star of Bethlehem because of the time of the year it is occurring.