The night sky has been illuminated by what appears to be a much bigger and brighter Moon.
The so-called "supermoon" occurs when the Moon reaches its closest point to earth, known as a perigee full moon.
The effect makes the Moon seem 14% bigger and 30% brighter than when it is furthest from the planet.
Skywatchers who miss the phenomenon this weekend because of cloudy skies will have to wait until August 2014 for the next one.
Space expert Heather Couper said "supermoons" were the result of coincidence.
"The Moon goes round in an oval orbit so it can come very close to us, and if that coincides with a full moon, then it can look absolutely enormous," she told BBC Radio 4's Today programme.
She explained that when the Moon was high in the sky, it looked normal.
But as it got closer to the horizon, a "kind of optical illusion" occurred where it looked bigger when compared with trees or houses, she said.
She suggested it might be possible to dispel the illusion by turning away from the Moon, bending over and looking at the sky from between your legs.
Writing in Sky and Telescope about the "myth of the supermoon", Shari Balouchi said much of what we called the supermoon was just our eyes playing tricks on us.
"The supermoon might look bigger than normal if you see it in the evening when the Moon's just rising, but the real size difference isn't big enough to notice."
BBC Weather's Darren Bett said he was confident most people in the UK would have been able to see the Moon at some point on Saturday night, even if only fleetingly.
Sunday night should be better, he added, with people in south-west England and south Wales likely to have the clearest views of the Moon.
However Marek Kukula, public astronomer at the Royal Observatory Greenwich, said people should not expect the supermoon to look that much bigger than normal.
"It won't fill the sky," he said.
"It's at its most impressive when the Moon is close to the horizon, ie when it's rising or setting - people will need to check online for rising and setting times for their locality."
Scientists have dismissed the idea that the perigee can cause strange behaviour, like lycanthropy or natural disasters.
Dr Couper said the tides this weekend would be unaffected.