A comet is delighting astronomers with a marvellous night-time display as it makes a near pass of the Earth.
The comet is breaking into fragments. (Image: European Southern Observatory)
The ball of ice, rock and dust has broken up into more than 60 pieces; two of the larger fragments are visible through binoculars or small telescopes.
At its closest approach this weekend, the comet will be some 10 million km (six million miles) from the Earth.
Continued disintegration means this may be the last swing around the Sun for Comet 73P/Schwassmann-Wachmann 3.
Dr Robert Massey, of the Royal Observatory, Greenwich, said the optimum time to see the comet in the UK was between 0000 and 0100 BST, away from the lights of the city.
He said observers should look East with binoculars and use a sky chart to get the best chance of a sighting.
"It's a rare opportunity for members of the public to see what is a pretty dramatic phenomenon," he said.
"Watching a comet break up is not something the public gets to do that often."
Comet 73P/Schwassmann-Wachmann 3 was discovered in 1930 by German astronomers. It orbits the Sun every 5.4 years.
It has an elongated path that swings out towards Jupiter then back towards the Earth and the Sun.
All periodic comets like this one are doomed to disintegrate and die. Astronomers first noticed in 1995 that Comet 73P had split into several chunks.
When it moved back towards the Sun in March this year, seven fragments were observed, of which two - B and C - were particularly bright. The break-up has continued apace.
Fragments B and C are expected to be visible between 11 and 14 May with binoculars and perhaps even the unaided eye.
If they fall apart still further - ejecting light-reflective material from the heart of the comet - they will be a magnificent sight in the night sky.
COMET 73P/SCHWASSMANN-WACHMANN 3 IN THE MAY SKY
To get the best view of the sky always move away from the city
The fragments are now moving across the Cygnus constellation
Look East and high with binoculars; fragment B has been brightest