Planets put on celestial show in December skies

If the skies are clear on the night of the winter solstice, you should look to the heavens for something that has not been witnessed for nearly 800 years.

About an hour after sunset, on the evening of December 21, low in the western sky, Jupiter and Saturn will appear closer together in the night sky than has been from Earth since the Middle Ages.

They will look like a double planet, appearing to be separated by only 1/5th the diameter of the full moon - when in reality they are more than 400million kilometres apart.

The last time these two planets were this close was in 1623 but they were too close to the sun for anyone on Earth to witness the event. The last time a so-called 'Great Conjunction' of Jupiter and Saturn was visible was March 4, 1226.

The planets have been moving closer in the night sky since summer and will be separated by less than the diameter of a full moon from December 16 through to Christmas Day.

For anyone with a telescope, clear skies willing, each planet and several of their largest moons should be visible in the same field of view that evening.

If you miss it, the solar system's two largest planets will repeat their celestial trick relatively soon. Set your calendars for March 15, 2089.