Saturn and Jupiter will come the closest they have done in hundreds of years, creating a “Christmas star” in what will be a super rare occurrence.
The two planets will create a “spectacular event in the sky” on Monday night as they happen to meet in a combined patch of the sky, giving the appearance of one star.
While the planets will actually still be roughly 400 million miles from one another, to the naked eye on Earth they will appear as one bright eye object.
The last time Jupiter and Saturn were this close together and visible was in 1226 AD.
Because of its appearance this year on the winter solstice, it is being described as the ‘Christmas Star’ in reference to the story of Jesus’ birth.
While the planets will be at their closest tomorrow, they are already visible in the night’s sky.
Weather permitting, the two planets will seem aligned in the UK on Sunday night, as well as Monday.
Professor Michael Burton said the biggest planets in the solar system will be just 0.1 degrees apart, one-fifth the diameter of the full moon, and appear as the brightest object in the sky.
Prof Burton, the director of Armagh Planetarium and Observatory in Northern Ireland, added: “When that [the 1623 conjuction] happened it was daytime.
“The last one which actually would have been well placed to be seen was 1226, 800 years.”
How to spot the Christmas star
NASA has shared some handy tips on how to spot the spectacle, the Daily Express reports.
The space agency said: “Find a spot with an unobstructed view of the sky, such as a field or park.
“Jupiter and Saturn are bright, so they can be seen even from most cities.
“An hour after sunset, look to the southwestern sky. Jupiter will look like a bright star and be easily visible.
“Saturn will be slightly fainter and will appear slightly above and to the left of Jupiter until December 21, when Jupiter will overtake it and they will reverse positions in the sky.
“The planets can be seen with the unaided eye, but if you have binoculars or a small telescope, you may be able to see Jupiter’s four large moons orbiting the giant planet.”
NASA Planetary Science Division astronomer Henry Throop described the phenomenon.
“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” he said.
“From our vantage point, we’ll be able to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”
“Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits,” Prof Throop explained.
“The date of the conjunction is determined by the positions of Jupiter, Saturn and the Earth in their paths around the sun, while the date of the solstice is determined by the tilt of Earth’s axis.”
When is the best time to see the Christmas star?
The best time to see the Great Conjunction will be shortly after sunset, hovering brightest next to the Moon between 4.30pm and 6pm.
This time, the conjunction will be most visible shortly after the Sun sets, giving the perfect spectacle to all across the Earth.
Binoculars or a telescope should enable viewers to see Jupiter’s four large moons.
The chance of clear skies is set to be greater in the northern half of the UK.