Jupiter and Saturn have crossed paths in the night sky, appearing to the naked eye as a "double planet".
The timing of this conjunction, as the celestial event is known, has caused some to suggest it may have been the source of a bright light in the sky 2,000 years ago.
That became known as the Star of Bethlehem.
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The planets have been moving closer together each night and reached their closest point on 21 December.
Jupiter and Saturn appeared closer to each other in the night sky tonight than they have in 800 years — forming a celestial beacon akin to the 'Star of Bethlehem'.
The gas giants — the largest planets in the solar system — have been slowly getting closer in the sky since the summer, and appeared like a double planet system.
Coinciding with the Winter Solstice, the conjunction could be viewed by eye from anywhere on Earth.
The planets looked around a fifth of a full moon's width apart earlier tonight — appearing low above the horizon in the UK — and can be seen for the rest of the week until Christmas Day.
The German astronomer Johannes Kepler wrote in 1614 that he believed the 'star of Bethlehem' in the Nativity story may have been a conjunction of Jupiter and Saturn.
Others researchers have suggested instead that the 'three wise men' may have followed a triple conjunction of Jupiter, Saturn and Venus.
While Venus won't be part of the this week's conjunction, it will still be an impressive astronomical site — one best viewed on the equator, but visible worldwide.
The event comes in a busy week for stargazers, with the Ursid meteor shower — the last for this year — peaking tonight and continuing into early tomorrow morning.
At its height, the shower will produce around five shooting stars an hour, which will burn up as they pass through the atmosphere at around 36 miles per second.
Like the conjunction, the Ursids will be visible to the naked eye — but will most easily seen in areas with little light pollution.
Astrophysicist Megan Argo of the University of Central Lancashire told BBC Radio 4 Today that the event was highly unusual.
'The best way to look is to go outside after sunset, by the time the sky has gone a bit dark and Jupiter should be the first thing you see in the night sky after the moon,' she explained.
The view will be best, Dr Argo added, from places with a good western horizon — clear of trees and buildings.
Those in London and New York saw the planets close to the horizon — at around 5.3° and 7.5°, respectively — around an hour after the sun sets tonight.
'Alignments between these two planets are rather rare, occurring once every 20 years or so,' said astronomer Patrick Hartigan of Rice University of Houston, Texas.
'But this conjunction is exceptionally rare because of how close the planets will appear to one another,' he explained.
'You’d have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky.'
A similar conjunction also occurred in 1623 — but at this time, the planets would have only been visible during the day, making them very difficult to see.
Source: dailymail
