(BBC) Thursdays and Saturdays are expected to cross paths in the night sky, appearing to the naked eye as a “double planet”.
The timing of this connection, as the heavenly event is known, has led some to suggest that it may have been a source of bright light in the sky 2,000 years ago.
That became the Star of Bethlehem.
The planets move closer to each other each night and reach their closest point on 21 December.
UK stars will have to keep a close eye on the weather to avoid astronomical disappointment.
“Any night it’s obviously worth a chance, because the weather doesn’t look great,” Dr Carolin Crawford of Cambridge University’s Institute of Astronomy told the BBC.
If there is a gap in winter darkness, both planets will appear in the southwest sky, just above the horizon just after sunset.
What hope for UK stars?
Monday is going to be a cloudy day with rain for some and while there was some hope a few days ago that the cloud will clear tonight, this now looks unlikely to most. There could be a few cloud breaks across England, the best of any clear sky will now be limited to Northern Ireland and the West of Scotland. You will need to look southwest, low on the horizon at dusk but before 6.30pm when Thursday and Saturday will lay below the horizon.
Is this the return of the Star of Bethlehem?
Some astronomers and theologians think so.
As Professor Eric M Vanden Eykel, a professor of religion from Ferrum College in Virginia, noted in an online article the timing has led to much speculation “about whether this might be the same astronomical event as Bible reports reported the wise men. to Joseph, Mary and the newly born Jesus ”.
That’s not just modern, Christmas speculation. The theory that the connection of Jupiter and Saturn could be the “Star of Wonder” in the early 17th Century was proposed by Johannes Kepler, a German astronomer and mathematician.
“2,000 years ago, people were much more aware of what was happening in the night sky,” said Dr Crawford, “[so] it is not impossible for the Star of Bethlehem to be a planetary alignment like this ”.
How rare is the event?
As planets cross paths on their journey around the Sun, conjunctions are not particularly rare, but this one is special.
“Touches are great things to see – they happen quite often – but [for the planets to be this close] quite amazing, ”Professor Tim O’Brien, an astrophysicist from the University of Manchester, told BBC News.
The two planets – the largest in the Solar System and some of the brightest objects in the night sky – have not been so close together in dark skies for 800 years. And while the UK forecast is not at all conducive to stargazing, it could change.
“It’s changing every hour – it’s just British weather and that’s astronomy for you,” said Professor O’Brien.
“The planets are going southwest, so you need to get out there as soon as the sky is dark.
“None of us are going to be around in another 400 years, so keep an eye on the weather and pop outside if you get the chance.”
By Victoria Gill, Science correspondent, BBC News