Stargazers are being warned they risk damaging their eyes by trying to view the rare spectacle of a bright comet today or tomorrow 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, but should delay their stargazing for a few days to await safer viewing conditions.
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.