By Dr David Whitehouse
BBC News Online science editor
Astronomers say there could be three comets visible to the unaided eye in the night sky in a few weeks' time.
Comet Bradfield passes the Sun
Comet Bradfield has just rounded the Sun and is heading for the dawn sky. It will be visible around 24 April.
Comet Linear, too, is promising and should be seen at northern latitudes in the morning sky on about the same date.
Finally, Comet Neat may be visible though experienced observers say it will be a week or two before it is known how bright the object will be.
Comet Bradfield was discovered by veteran comet hunter William Bradfield of Australia. He saw it on 23 March whilst sweeping the evening twilight with his home-made telescope.
Bradfield has discovered 18 comets since he first started looking in 1972.
On 19 April, the comet was captured in an image taken by the Solar Heliospheric Observatory (Soho) satellite as it passed close to the Sun. At its closest, the comet was well inside the orbit Mercury - the closest planet to the Sun.
It should be visible to the unaided eye when it moves further away from the Sun in the coming weeks.
There are two other comets in the sky that should be visible without a telescope, although astronomers warn that predicting a comet's brightness is tricky.
Comet Linear was found in 2002 by the Linear automated sky survey project. During the last week of April, it should appear in the morning sky in the constellation of Pisces, just above the eastern horizon at dawn.
Comet Linear's dust tail
Remarkable pictures of it have been taken by astronomers Gianluca Masi and Franco Mallia, from the Campo Catino Observatory in Italy, using the Las Campanas telescope in Chile.
"It was only a few degrees above the horizon but the images we obtained of it were great," Gianluca Masi told BBC News Online.
"The images showed an amazing, detailed-rich tail."
From the Northern Hemisphere, Comet Linear will be difficult to see as it will be low down in the morning twilight.
The third comet, Comet Neat, found by the Near Earth Asteroid Tracking project, is a little more uncertain than the other two.
Astronomers will know more when it has had its encounter with the Sun. It should be visible low on the southeast horizon in the last week of April.
"We have been following the comet over the past few months as it increased in brightness and started showing a tail of gas and dust," Gianluca Masi said.
"We decided to take a detailed picture that shows some very interesting structures in the tail. We believe they are dust waves."
Part of the uncertainty stems from the fact that Comets Linear and Neat are thought to be comets making their first approach to the Sun, and such first-timers are always a little unpredictable.