We are in for a treat this year with a planetary conjunction of our Solar System's two largest planets--Jupiter and Saturn. This is an event that occurs on average every 19.6 years. Due to the tilt of the orbital planes of the two planets they may seem to go above or below each other. This year Jupiter will appear just south of Saturn. The minimum distance separating them will be approximately 6 arcminutes. The Full Moon is about 30 arcminutes so the separation between the two planets will be about 1/5 the diameter of a Full Moon.
If you look to the southwestern sky after sunset you will see Jupiter and Saturn low but visible to the unaided eye. Jupiter is more southerly and westerly than the ringed planet. Watch each night as they appear to get closer to one another in the sky. Don't worry: they are separated radially by several hundred million kilometers so they won't bump into each other!
On December 21, at sunset, they will be at their closest separation since 1623. In 1623 however, they appeared closer to the Sun so it was more difficult to see even with the decade old invention of the telescope.
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| Jupiter/Saturn Conjunction - December 21, 2020 |
Don't be concerned if it is cloudy or you forget, they will be very close to each other for several days before and after the 21st. They will fit into most telescope fields of view for more than a week before and after and the same binocular field for a month before and after! The fields of view of average astronomy equipment are shown below for December 21.
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| Jupiter/Saturn Conjunction Fields of View |
The conjunction occurs at declination of -20.5° which means it will not be visible to those few hundred thousand people living in the cold northern climes above 69.5°N latitude. In the south, the Sun is at -23.5°S so those below 66.5°S latitude are experiencing permanent Summer sunlight and will not be able to see the event without specialized equipment. Anyone close to those latitudes will certainly have a lot of trouble seeing the event.
However, it will be visible to those with clear skies at any longitude in between these latitudes. At any given time during the year the Earth faces the same area of the sky and anyone at the same latitude will see the same thing at the same local time. The sky at 5pm in Calgary will be very similar to 5pm in London, England as they are both approximately 51°N.
Is this an event that only happens once? No. As mentioned above these two planets are in conjunction every 19.6 years. Sometimes they are closer, sometimes they are further away from each other. In the 7000s CE they will be so close that Jupiter will eclipse Saturn! Are planetary conjunctions rare in general? No. There will be three conjunctions in January 2021: (Mercury/Jupiter, Mercury/Saturn, Mars/Uranus).
Major and Minor News Outlets have not been completely accurate in their reporting of this event so it is best to ask a local astronomer if you have any questions related to this conjunction or any other event that happens in the night sky. Misinformation is breeding on social media due to inaccurate reporting so before you share anything please fact check.
