On December 21, 2020, we will witness a Great Conjunction that has not happened since 1623. Credit: NASA / Lunar and Planetary Institute

A Cosmic Spectacle: December 2020 Great Conjunction Hasn’t Occurred Since 1623

Great Conjunctions occur once every 20 years but the last time Jupiter and Saturn were this close was in 1623.


Sometimes I think that many of us are so used to seeing the sky that sometimes we forget to really enjoy it. For those of us for whom it is of greater interest, we still have plenty of wonderful astronomical events yet to come before 2021.

This year, we witnessed an absolute celestial show, but the climax is coming on December 21 – the Great Conjunction of Jupiter, Saturn, and the Moon.


Before we talk about it, let me mention that even in the remaining few days of November, you have the chance to enjoy two astronomical events – the gathering of Mars with the Moon on November 25, and the Penumbral eclipse on the night between November 29 and 30.

You can find out more about these events in our special article on astronomical events here. Now, let’s discuss the Great Conjunction of 2020 and why it is more special than most of the previous ones.

The Great Conjunction of 2020: an astronomical event that has not occurred since 1623

You may ask why this conjunction is any different than the previous ones seen throughout this year. It is true that Saturn, Jupiter, and the Moon formed a triangle in the sky in March, and they were also partly visible again in the past months. What will be different on December 21 during the Great Conjunction?

What makes a Great Conjunction is the short distance between Saturn and Jupiter on that specific occasion. Yes, conjunctions happen regularly but a “great” one only occurs once every 20 years. More specifically, once every 19,6 years.


The orbital period around the Sun of Saturn takes approximately 29.5 years while Jupiter completes a single orbit in 11.86 years. Due to this combined effect, a Great Conjunction is possible only once every 20 years and the 2020 edition will be the most important one in nearly 400 years.

The last time Jupiter and Saturn were this close to each other occurred in 1623, making this Great Conjunction an unmissable astronomical event. The three celestial objects will form a perfect triangle in the sky and here is how you can witness it.

Of course, the Great Conjunction will be visible with the naked eye as it has been in the past few months since their conjunction began.

However, observation of the phenomenon will be more difficult than before since it will be the final day for observation for this year. The Great Conjunction will be visibly low above the southwestern horizon, in the fading glow after sunset.

You should be able to observe Jupiter and Saturn for about 1 hour and 15 minutes after sunset. With this in mind, observers should choose a place with a low horizon to the southwest. Using binoculars will help both planets be detected earlier in the twilight. Of course, you can also use a telescope.


The gas giants can be observed together in the eyepiece of a high-magnification telescope with about 400x zoom or more if the instrument allows. We highly recommend getting one or borrowing one for this astronomical event. If not, simply look at the Moon and you will see how it forms a perfect triangle with Saturn and Jupiter. 

Of course, this century will be marked by four more Great Conjunctions, the next being on October 31, 2040. BUT, we will never be able to see them this close to each other again during our lifetime.

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Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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