The Great Conjunction

BEST TIME TO SEE: 20, 21 and 22 December, narrowest separation on the 21st; view 40 minutes after sunset

Jupiter and Saturn have appeared close to one another since they crawled out of the morning twilight last February. After a brief divergence in the early summer months, since late August, to the naked eye they have steadily appeared to be getting closer.

At the start of December, their separation will be 2.2˚, and this gradually reduces over the month to reach a historically low 6.1 arcminutes on the evening of the 21st. To put this in context, the apparent diameter of the Moon is around 30 arcminutes. At their closest, Jupiter and Saturn will appear separated by just one-fifth the apparent size of the Moon. Visible shortly after sunset on the 21st, this ‘Great Conjunction’ will present the planets at their closest since July 1623!

At first glance with the naked eye, the planets will appear as one bright object, Jupiter’s brightness at mag. –1.8 masking Saturn at mag. +0.9. But take a closer look and you may make out the fainter point of the Ringed Planet just above it.

Of course, their apparent proximity is simply due to line-of-sight; in reality, they are physically separated by 733 million km. But the sight of two bright planets so close to one another is something quite special.

A telescope will show both planets in the same field of view, each as a tangible disc. In order to do this, you’ll need to use a magnification of 150x to 200x. Although the planets will appear small, this is a unique opportunity to see them and their brighter moons like this.

And speaking of natural satellites, the waxing crescent Moon will appear nearby on the evenings of 16 and 17 December, adding its own photogenic essence to the Great Conjunction.

150x magnification: an inverted (south-up) view, approximately one hour after sunset ▲ Don’t miss December’s Great Conjuction of Jupiter and Saturn; to see both planets at the same time through a telescope, you’ll need a magnification of 150x to 200x