Get Ready For ‘Great Conjunction’ As Jupiter And Saturn Move Closer After 397 Years

Get Ready For ‘Great Conjunction’ As Jupiter And Saturn Move Closer After 397 Years

In their closest encounter since 1623, Jupiter and Saturn appear as a single star in the evening sky next month.

There is a celestial event known as the "Great Conjunction" which is set to take place on December 21 of this year. The planets Jupiter and Saturn will be visible about one-tenth of a degree apart, marking their closest approach since 1623. We have been pretty excited about these two gas giants of the solar system all year long. Jupiter and Saturn have been particularly evident in the southern evening sky, moving very close to each other from our point of view on Earth, according to Space.com. Saturn is the farthest and slowest-moving planet from the Sun that we can easily see with our naked eye. After that is Jupiter, the second-slowest bright planet, and the largest in the solar system. 



Jupiter, being one of the more brilliant and brighter nighttime objects has been standing out even more so due to the presence of Saturn trailing just off to its left - that is, the east. Appearing about one-twelfth as bright, Saturn has, in a way, served as Jupiter's "lieutenant" in this year of 2020. When Jupiter and Saturn have the same right ascension or celestial longitude, it is said that they are in the "Great Conjunction." The average frequency of occurrence is merely the product of their sidereal periods divided by the absolute value of their difference. 



What is a sidereal period? Well, we can define it as the time taken by a celestial body within the solar system to complete one revolution with respect to the fixed stars. Saturn's period of 29.65 years, multiplied by Jupiter's period of 11.86 years amounts to 351.65. Dividing this value by the difference in their sidereal periods gives us 19.76 years.  So, about every 20 years, Jupiter and Saturn will have a rendezvous and the next one is coming very soon; in fact, it is scheduled for next month scheduled on Dec. 21. Usually, Jupiter tends to overtake Saturn by more than a degree. That will change on December 21, as they will be separated by just about one-tenth of a degree.





The great conjunction occurs 7 weeks after Jupiter passes Saturn in heliocentric longitude - heliocentric conjunction. For this year, the two planets will be visible low above the southwestern horizon in the constellation of Capricornus after sunset. From mid-northern latitudes, the planets will be less than 15° in altitude, one hour after sunset. There is no other combination of the pair until October 31, 2040, when the two would travel slightly further apart in the pre-dawn night sky, Jupiter and Saturn's nearest conjunction after 1623. "Overall – from October 21 to December 21, 2020 – Jupiter will have traveled 11 degrees and Saturn 5 degrees. Bingo! That’ll completely close the 6-degree gap that separated Jupiter and Saturn on October 21, 2020!" EarthSky reported. 



After this year's "Great Conjunction", both Saturn and Jupiter will appear to swap positions, as Jupiter will then overtake Saturn. Jupiter will then progress to the east and draw farther and farther away from Saturn throughout the decade 2020-2030. Following that, the two planets will approach each other through the 2030s, reaching the "Great Conjunction" once again in November 2040. Beyond that, Jupiter-Saturn conjunctions will occur in April 2060, March 2080, and September 2100.


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