Great Conjunctions are pretty cool – Jupiter and Saturn line up and appear close together from our viewpoint. They occur somewhat rarely but regularly (about 20 years apart) due to the orbital periods of Jupiter (11.9 years) and Saturn (29.5 years). The next Great Conjunction, coming up in a few weeks on Dec 21st, 2020, is an extra-special one.
It is extra-special because Jupiter and Saturn will be extremely close together, just over 6 arc-minutes apart. You would have to go back almost 400 years to July 16th, 1623 to find them as close! To help visualize it, hold out your pinkie finder at arm’s length, that covers about 1°, so at conjunction, the two planets will be separated by a distance equal to about 1/10 the width of your pinkie – that is close enough that the two will appear as a single bright star to the naked eye. They will appear low to the horizon in the South-West around sunset on Dec 21st (sunset is at 4:15 pm PST).
There’s no need to wait until Dec 21st as Jupiter and Saturn are already quite close together, starting off December about 2° apart. Both will easily fit within a 1° field of view (typical of common telescopes) from Dec 17th through to Dec 25th.
| Date | Separation (arc-minutes) |
| Dec 17 | 28 |
| Dec 18 | 18 |
| Dec 19 | 13 |
| Dec 20 | 8 |
| Dec 21 | 6 |
| Dec 22 | 11 |
| Dec 23 | 16 |
| Dec 24 | 22 |
| Dec 25 | 29 |
The low altitude and weather will be challenges for observing the conjunction from Vancouver. You may want to watch a live-streamed event from a remote location rather than betting on clear skies in December in Vancouver – Virtual Telescope, for example, is hosting a live-streamed event.
Sky-At-Night magazine has an article on the Great Conjunction with more info, and you can get some general observing tips from SkyNews’s Guide to Observing Jupiter.