Jupiter and Saturn converge towards the closest conjunction in 400 years

The giant planets Jupiter and Saturn are closing in for a rare sight not seen since the Middle Ages. The two worlds have been shining together in the constellation Sagittarius in the southern sky for many months.

They are gradually getting closer and on December 21, 2020, a few days before Christmas, they resemble a bright “double star” after sunset.

Obviously it will be a line of sight effect, as Saturn is far beyond Jupiter in the Solar System and will actually be 733 million km from it.

But at the closest moment, the two planets will appear separated by just 6.1 minutes of arc, which is only a fifth of the apparent diameter of the Moon in the sky.

Due to the timing, the event is compared by some to the Star of Bethlehem, an event that some have attributed to a planetary conjunction, if it were not simply a legend.

The planets are nearing the end of their current appearances, so both will only be visible in the early part of the evening before sunset.

For those in the northern latitudes, you’ll need to look down southwest, as soon as it gets dark, to spot the pair. Both are bright, although Jupiter is notably the brighter of the two.

The conjunction will be higher in the sky for southern hemisphere astronomers.

The planets will be so close that it will be possible to see them both, plus their brighter moons, in the same field of view with a telescope and a moderate power eyepiece.

The conjunction is the closest the two planets have appeared in the sky for nearly 400 years – the last time was in July 1623.

If it is cloudy on the night of the closest approach, you will be able to see the planets a little more distant in the evenings on either side of 21.

They will be separated by a diameter less than the apparent diameter of the Moon between the dates of December 16-25, 2020.

In addition to being of visual interest, the combination offers great opportunities to capture a great photo. With the two planets low in the twilight sky, it should be possible to add an interesting foreground to your composition.