Stargazers are being warned they risk damaging their eyes by trying to view the rare spectacle of a bright comet as it flies near the sun.
The C/2011 L4, also known as Comet Pan-Starrs, is making a rare visit to the inner solar system and will not be back for 110,000 years.
However, experts warned that amateurs should not try to see it too soon.
Rev Kate Kay, chief astronomer at the Norman Lockyer Observatory in Sidmouth, Devon, said: "It's going around the sun, and there is always a danger that if you try to look at it when it is near the sun, you are going to do some damage to your eyes.
"We're hoping to get our first glimpses and photographs of it on Tuesday and Wednesday when it's away from the sun, and near the new moon. If people look then for the moon, just to the right of it, they may see a little white smudge, hopefully with a nice tail.
"With any luck this bad weather may have improved by then, allowing young people with stronger eyes to see it, or older people with binoculars."
The comet is named after the Hawaiian telescope with which astronomers first spotted it in June 2011.
Members of the Flamsteed Astronomy Society, which is part of the Royal Observatory, are planning to look for the comet from Blackheath in south-east London on Friday, or Saturday if the weather is bad on Friday.
Joint vice chairman Grey Lipley said: "If you are going to try to find the comet while it is near the sun, you should wait until the sun is fully set. But it is going to be difficult to see it given the poor weather at the moment."