Great Conjunction of Jupiter and Saturn, December 2020

Jupiter takes twelve years to complete one orbit of the Sun, while Saturn takes about 29.5 years. Consequently Jupiter takes less time to complete one circuit of the zodiacal constellations than Saturn does. Every twenty years or so Jupiter's faster motion causes it to "catch up" to Saturn to create an event known as a "Great Conjunction" where the two planets appear close together in the sky. These events were significant in ancient times as both Jupiter and Saturn were considered to be important gods in their religious beliefs. 

During late December 2020 Jupiter eventually caught up with Saturn to participate in an especially close Great Conjunction. The planets were just 6 arcmin (0.1) apart in the sky at 18:20h UTC on the 21st December and both planets were visible together in the same field of view in amateur telescopes. This was the closest approach in almost 400 years (last in 1623) and just six occur in the 1000 years from 1600, truly indicative of the relative rarity of such events. Note the changing orientation of Jupiter's moons from night to night.


18th December

the planets adorn the roof of a tall office block.
19th December
Jupiter is a little closer to Saturn as viewed against a date palm at St Kilda
A very close view.

20th December

A wide-angle view in the twilight from Port Melbourne.
A closer view.
21st December
The night of closest approach. A wide-angle view in clear skies at Ouyen, north-western Victoria.
The planets together over the roof house of one of the grain silos in town.
The planets as would be seen through a telescope under moderate magnification. Jupiter's Great Red Spot, atmospheric belts and its moons together with Saturn are clearly visible. A once-in-a-lifetime event for me.


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