The countdown is on for the great conjunction of Jupiter and Saturn. The two giant planets of the Solar System will lie a mere six arcminutes (0.1 degree) apart, only one-fifth of the diameter of the full Moon, on next Monday, 21 December.
Saturn lies above Jupiter as they lie above the north London rooftops on 12 December. Image: David Arditti.
One could describe this event as being almost 400 years, or even 800 years in the making. The last time the two gas giants were this close was in July 1623, about 20 years before the outbreak of the English civil war and when Galileo Galilei was peering through his crude telescopes. If fact, Galileo would have struggled to see this conjunction, owing to the fact that Jupiter and Saturn were placed just 13 degrees from the Sun.
We have to go back a further 400 years or so, to March 1226, not long after the Magna Carta (‘Great Charter’) was signed and Henry III was King of England, to find a conjunction between the two gas giants that was observable; on this occasion they were separated by just two arcminutes!
Conjunctions of Jupiter and Saturn are the rarest ...