Pre-dawn meet for Jupiter and Venus
A dazzling conjunction of Jupiter and Venus could lead to a flurry of UFO sightings early on Monday.
The two brightest planets in the sky will form a spectacular "double star" hanging low on the north-eastern horizon.
They can be seen shortly before sunrise at around 5am appearing only 0.2 degrees apart - less than half the width of a little finger held out at arm's length.
It will be the closest conjunction of Venus and Jupiter since 2000.
Their combined brightness and low position in the sky could keep police and Ministry of Defence switchboards busy with reports of UFOs.
Robin Scagell, vice-president of the Society for Popular Astronomy, said: "They will be so close together that it's going to be quite a striking sight.
"Undoubtedly people could mistake them for a UFO, especially being so low down. They might appear to move around because of the distortion effect of the atmosphere."
Although the planets appear to be kissing-distance apart as seen from the Earth, they are actually separated by hundreds of millions of miles.
Venus and Jupiter pair up about once a year on average, but their conjunctions vary greatly in separation and visibility. Some are missed completely because they occur in daylight.
The next Venus-Jupiter conjunction is due to occur on June 30 next year, but will be less close.
During Monday's conjunction, Venus will appear six times brighter than Jupiter even though its diameter is less than a tenth that of the larger planet, which measures 86,881 miles across.
That is because Venus is much closer to the Earth and also nearer the Sun, causing its clouds to be lit more intensely.
A pair of binoculars will heighten the conjunction experience, but a small telescope promises a dramatic view.
Venus will mimic a tiny full moon, while Jupiter appears three times wider. Jupiter will also be accompanied by its four brightest moons strung out in a row.
Ideally the conjunction should be seen from a high unobstructed vantage point.
"People who have buildings, hills or trees in the way might miss it, but even a roof top in London should offer a good view," said Mr Scagell.