By Dr David Whitehouse
BBC News Online science editor
A total lunar eclipse will be visible on Saturday from Europe, Africa, the Americas, and much of Asia - if the weather is kind and gives clear skies.
The Moon regularly passes into the Earth's shadow and becomes dimmer. It happens about every six months or so.
A lunar eclipse has no great importance astronomically but can be enjoyed by many people without special equipment.
Skywatchers should train their eyes on the Moon from 2215 GMT, when it enters the outer edges of our planet's shadow.
In the UK, the Campaign for the Protection of Rural England is using the eclipse to highlight the problem of light pollution.
Majestic clockwork
Mid-eclipse takes place between 0106 and 0131 GMT Sunday as the Moon transits the southern edge of the Earth's shadow.
WHERE IT WILL BE SEEN
America, Europe, Africa and parts of Asia
Dust and cloud in Earth's atmosphere may affect the Moon's colour
Totality is quite short this time because the Moon only passes just inside the full shadow of the Earth, and the Moon's southern edge, in particular, should remain fairly bright.
As the show progresses, the Moon will get dimmer and, possibly, turn reddish during mid-eclipse, when the only light that can reach the lunar surface is red light refracted through the Earth's atmosphere.
Astronomers will be scrutinising the Moon's surface through telescopes to note how its appearance changes as the Sun is obscured by the Earth.
The Moon leaves the last bit of shadow at 0422 GMT.
Skywatchers in North America will see the eclipse begin in twilight as the Moon rises on Saturday evening. It will all be over by US midnight.
Imperturbable serenity
Although lunar eclipses have no great scientific significance, they are a spectacle of nature that delights and enthrals.
In the past things were different. It was a portent from the sky, possibly a sign of divine displeasure.
TOTAL LUNAR ECLIPSE
Occurs when Moon passes into Earth's shadow
Penumbra: Region where Earth blocks some (but not all) Sun rays
Umbra: Zone where Earth blocks all direct sunlight - total eclipse
But as superstition has given way to reason, a lunar eclipse has rightly come to be regarded as an example of the majestic clockwork of the heavens.
Thomas Hardy said the movement of the Earth's shadow over the Moon had an "imperturbable serenity".
The colour effect is the stuff of myth and legend. An account in 331 BC said: "...all her light was sullied and suffused with the hue of blood."
Some ancients called it "the time of the blood of the Great Mother's wisdom", linking the Moon's colour with menstruation.
This was a natural thing to do given the link between the length of the month and human fertility.
Ugly orange glow
In 1503, Christopher Columbus, stranded in the Caribbean, used a lunar eclipse he knew would take place to impress the natives and secure respect and fear, as well as a regular supply of food.
In the UK, countryside campaigners are using the eclipse to highlight the increasing problem of light pollution of the night sky.
The say the Moon may be visible but scattered light from towns and cities is snuffing out the stars.
"A lunar eclipse is spectacular, but more often than not the sky in which it appears is smeared with an ugly orange glow from light pollution," said Tom Oliver, the CPRE's head of rural policy.
"Why should thoughtless, wasteful outdoor lighting spoil so many people's views of the heavens?"
