How to watch tonight’s Great Conjunction


Skywatchers are in for a Christmas treat, as the two biggest planets come the closest they have since the days of Galileo.

The one-in-200-year "Christmas Star" will light up skies across the world for two weeks, with the peak "planetary kiss" between Jupiter and Saturn to happen on Monday night.

The Christmas Star is an "especially vibrant planetary conjunction" easily visible in the early evening over the next two weeks, as the two giants come together.

Every 20 years the planets align, however on Monday night they will be at their closest point in almost 400 years, making this a cosmic event not to be missed.

In addition, it's been almost 800 years since the planets aligned at night, meaning this out-of-this-world event is one everyone can witness.

Known as the "Great Conjunction", it last occurred in 1623, caught by Galileo Galilei, when Jupiter caught up to, and passed Saturn as they travelled together across the sky.

During the last Great Conjunction, the planets were separated by little more than 1 degree - just wider than two full moons.

This year, it's estimated they will be separated by just 0.01 degree according to the Perth Observatory.

The view of Jupiter and Saturn through a pair of 7x50 binoculars on Monday evening. DIAGRAM: Martin George
The view of Jupiter and Saturn through a pair of 7x50 binoculars on Monday evening. DIAGRAM: Martin George

Despite the illusion, the planets are actually separated by more than 700 million kilometres.

According to NASA, the closest alignment will last for a few days, but on Monday they will appear so close together that "a pinky fingers at arms length will easily cover both planets in the sky".

"The planets will be easy to see with the unaided eye by looking toward the southwest just after sunset," a NASA spokesman said.

The Perth Observatory said the reason it was known as the Christmas star is that some astronomers believe it is the famous Star of Bethlehem from the Bible nativity story.

Here's how you can see the phenomenon for yourself:

  • Find a spot with an unobstructed view to the west, and the pair will appear not long after sunset.
  • Looking low to the west, Jupiter will be on the left and Saturn to the right at about the 4 o'clock position from Jupiter.
  • No need for binoculars or a telescope, as this cosmic event will be easily visible (provided there are no clouds) to the naked eye.
  • If you do have binoculars or a telescope, you can possibly make out Jupiter's moons or Saturn's rings.

If you miss this, it won't be long - cosmically speaking - until the next "Great Conjunction", which will happen on March 15, 2080. Jupiter and Saturn will once again shine 0.06 degrees apart, higher up in the night sky.

Originally published as How to watch tonight's Great Conjunction