Jupiter and Venus will form a `double star' and appear only 0.2 degrees apart as a result of a dazzling conjunction early on Monday, which could lead to a flurry of UFO sightings.
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.
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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."
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.
