The winter solstice this year coincides with one of the most interesting astronomical events in 2021: the great conjunction of Jupiter and Saturn, which at the twilight of December 21 will make the two largest planets of the Solar System appear very close in the sky to form a very bright object.

Conjunctions between Jupiter and Saturn are periodic events that occur every 20 years or so, but they can be more or less "narrow": from a separation of a few degrees, that is a distance greater than the apparent diameter of the Moon, up to really close encounters, in which the two planets practically merge with each other.

This 2021 conjunction is one of these very close conjunctions: on the evening of December 21, the angular separation between Jupiter and Saturn will be just one-tenth of a degree, that is, one-fifth of the apparent diameter of the Moon.

To find a similar one you have to go back almost 400 years, to the evening of 1623. From the chronicles of the time, however, it seems that the two planets met in an unfavorable position for observation: too close to the Sun to be able to see them with the naked eye. The previous great conjunction so close dates back to 1226, and on that occasion (as will happen this year) the observation conditions should have allowed the spectacle to be enjoyed even with the naked eye. This means that, clouds permitting, on the evening of the winter solstice we will be the first men to observe the two planets so close in the sky for just under 800 years.

Jupiter and Saturn have already been visible in the sky for some months and will continue to approach until December 21, reaching the minimum distance between them at the twilight of the winter solstice.

In order not to miss the show, you need to find a location that has no obstacles to the south-west, because Jupiter (the brightest) and Saturn will appear low on the horizon in the direction of the sunset. The conjunction will also be visible to the naked eye, with some difficulty in recognizing both planets distinctly. But with binoculars, things should get easier, while telescope owners will have no problem enjoying the show in all its glory.

Here is the live broadcast of the event, organized by INAF - National Institute of Astrophysics, on 21 December at 17:00: