Planets Jupiter and Saturn will be seen very close to each other on 21 December. According to a report by Chron, they will align to form a spectacular phenomenon in the night sky called a 'double planet'. As per a statement by Earth Sky, the date of the conjunction is, coincidentally, the date of the December solstice. It will also be the first Jupiter-Saturn conjunction since the year 2000, and the closest one since 1623, fourteen years after Galileo made his telescope.
The statement adds that however, the conjunction was only 13 degrees east of the sun. The closest observable Jupiter-Saturn conjunction happened in 1226. The conjunction that will happen in December will see Jupiter and Saturn be only 0.1 degree apart.
EarthSky adds that the conjunction in 2020 won’t be matched again until the Jupiter-Saturn conjunction of 15 March 2080.
The Jupiter-Saturn conjunction
Every year, Saturn completes about 12 degrees of its orbit around the sun, while Jupiter completes 30 degrees. In one year, Jupiter closes the gap between the two by about 18 degrees. In every 20 years, Jupiter gains 369 degrees on Saturn, therefore lapping the ringed planet in every two decades.
From 15 December, 30 minutes after sunset, one may see a thin lunar crescent above the horizon. The next day, the lunar crescent will be seen clearly right below the planets and on 17 December, the crescent will have moved further up. Between 20 and 21 December, the two planets will become so close together that they will not be able to be separately distinguished.
The best viewing conditions will be near the equator and the further north one views the phenomenon from, the less time they will have to catch a glimpse of the rare occurrence, before the planet sinks below the horizon.
source https://www.firstpost.com/tech/science/jupiter-and-saturn-to-align-in-rare-double-planet-conjunction-on-21-december-9074061.html
