Jupiter and Saturn (bright light, centre) in a planetary conjunction seen at twilight. Planetary conjunctions occur when two planets are seen close together in the sky as viewed from Earth. This is the 'Great Conjunction' of the 21st December 2020 when the planets reached their closest alignment, a tenth of a degree apart. The last 'Great Conjunction' of Saturn and Jupiter as close together occurred over 800 years ago. Photographed near Alqueva Lake, Alqueva Dark Sky Reserve, Portugal.