By Dr David Whitehouse BBC News Online science editor

Skywatchers gazing at the heavens just after sunset during the next few days should get a glimpse of a cosmic wanderer - Comet Ikeya-Zhang.

The comet is a surprise visitor to the inner Solar System, having appeared without warning a few weeks ago.

It's the best Northern-Hemisphere comet since Comet Hale-Bopp in 1997

Martin Mobberley, British Astronomical Association

The object, first picked up by two amateur astronomers in Japan and China, is hovering on the limits of unaided-eye visibility but is a spectacular sight in binoculars for those looking from the Northern Hemisphere.

In a few days, Ikeya-Zhang will round the Sun and appear on the star's other side in Earth's pre-dawn sky, where it should also make a fine spectacle.

But astronomers warn casual observers that they should never look directly at the Sun with either the naked eye or any optical aid as blindness can result.

Evening object

According to Denis Buczynski of Conder Brow Observatory near Lancaster, UK, the comet is remarkable for two reasons.

"First, that it was discovered visually. These days, most comets are discovered by automatic patrols.

Martin Mobberley's close-up on the comet

"Secondly, it is a return of a comet last seen in the 1600s. No other comet with such a long period has been observed on subsequent returns before."

The comet hangs in the star fields of the constellation of Pisces, not far from the Sun after it sets. Over the next few days, a good view should be had between 1900 and 2000 GMT.

Martin Mobberley of the British Astronomical Association has been following the progress of the comet.

He said: "From a country site it can be seen as an extra star. The comet's gas tail is not hard to spot in binoculars... it stretches upwards from the comet into the evening twilight."

Best period

Denis Buczynski told BBC News Online: "The comet's head is almost star-like with a hint of fuzziness around it from which flows a long tail which broadens and splits about a degree or so along its length."

The view in binoculars or a telescope shows a wealth of detail along the length of the tail, with knots and kinks caused by the outflowing of gases and dust from the comet's head interacting with the solar wind.

"The comet reaches its closest approach to the Sun in a few days' time, after which it will then appear in the north-western pre-dawn sky," Denis Buczynski said.

"Although the comet will be receding from the Sun, it will come closer to the Earth on its outward bound journey and should still appear as bright as it is now."

Martin Mobberley added: "This will probably be its best period.

"It's the best Northern-Hemisphere comet since Comet Hale-Bopp in 1997, but will probably peak at less than a 10th the brightness of that monster and the superb 1996 comet Hyakutake."