Millions across the Western hemisphere will have the chance to see the Moon turn red during the year's only total lunar eclipse early on Thursday morning, astronomers said on Wednesday.

The eclipse will be visible across Western Europe, northwest Africa, the eastern half of North America and the whole of South America, according to the Royal Astronomical Society in London.

The full Moon will turn yellowish and then appear blood red, rusty or grey, depending on the atmospheric conditions on Earth.

"The lunar eclipse promises to be a spectacular sight," a Royal Astronomical Society spokesman said. "Unlike the solar equivalent, the whole event is quite safe to watch and needs no special equipment."

During the eclipse, the Earth will line up directly between the Sun and the Moon, which will be covered by the Earth's shadow.

Sunlight will pass through the edge of the Earth's atmosphere, scattering blue light and giving the Moon a reddish hue.

The Moon should turn red by about 3 a.m. the eclipse will end by about 6 a.m.

The Moon will be in front of the Leo constellation, with the bright star Regulus to its right and Saturn to its left.

The next total lunar eclipse won't be seen until December 2010.