Image copyright Facebook Image caption You can see the Beaver ‘blood moon’ in the US state of Oregon on 21 November
People on the Pacific coast of the US will see the longest total lunar eclipse of the century – beginning at 1230 GMT, ending just before 0200 GMT.
It’s one of three lunar eclipses which will occur in just four days.
But observers in Europe and Africa will have a more early-morning viewing opportunity.
In Japan, the eclipse will not begin until around 0200 local time, meaning the moon will not be seen until Thursday morning.
Image copyright NASA Image caption Nasa released this image before the eclipse, showing the “blood moon”
The US state of Oregon has also joined other states in taking to social media to encourage people to take in the lunar event.
Great news. We’re about to witness a once in a lifetime event. Find a partner, plan a family dinner & watch the eclipse together. #rosetheresoon pic.twitter.com/9T7EUyyE4N — Oregon Tourism (@OregonTourism) November 19, 2017
The Federal Bureau of Investigation said it would monitor activity on social media for any unusual happenings during the eclipse.
“Due to its time of day, this eclipse might have more potential to disrupt the normal operating environment,” FBI spokeswoman Kathy Wright said.
Image copyright Itochu Image caption Bird watching fans in Japan have also been urged to take advantage of the eclipse
With the eclipse appearing at various times across the world, it is likely to be a rare opportunity for amateur astronomers, scientists and the general public to spot a number of interesting sights.
In China, thousands of children have been flocking to the scenic Hatan Maling National Nature Reserve to catch a glimpse of the rare event.
Image copyright Itochu Image caption In Japan, the eclipse will begin at 01:47 on Wednesday morning.
Tibetan monks will spend time seeking enlightenment on the slopes of Mount Everest, as the moon dips beneath the peak.
Volunteers in Nepal and China have also been put to work during the eclipse, preparing for the “fasted-for” period when the Earth will be at its furthest from the sun.
Image copyright Itochu Image caption Birders in Japan have also been encouraged to take advantage of the eclipse
What is a total lunar eclipse?
According to Nasa, a total lunar eclipse occurs when the sun, Earth and moon are in a line. The Earth’s shadow blocks out the sun’s light, casting a blood-red or brownish tint on the moon.
The eclipse is not visible in all areas at the same time because the orbits of the Earth and the moon pass through different sections of space.
Image copyright AFP Image caption Parts of India could see a partial eclipse
Although the lunar eclipse is an almost total eclipse, the moon doesn’t completely disappear from view.
This gives observers the chance to take in a broad, deep sight of the moon and its shadow.
Image copyright ADN Image caption Heavy cloud cover will obscure the eclipse in parts of Europe
The next total lunar eclipse will not happen until 2033, but astronomers say it can only happen once in every two years.
It is likely to coincide with a total solar eclipse, when the moon crosses directly between the sun and the earth, leaving a sunshade on the sun’s surface.
Image copyright NASA Image caption A similar total lunar eclipse will take place on 3 January 2019
A complete eclipse is unlikely to occur again for almost a billion years.
The eclipse will be particularly dramatic in some areas of the Pacific region where the sun sets earlier and falls below the horizon, obscuring the moon.
Several minutes before totality begins, the moon will become obscured by the Earth’s shadow.
The moon will then appear to rise above the horizon in the west, before falling back to the east when the full eclipse begins.
Image copyright NASA Image caption The eclipse is expected to last for almost four hours
The blood effect is made more noticeable as temperatures dip during the eclipse.
Nasa astronomers forecast that the total eclipse will last for four hours, with the moon reaching totality between 1342 GMT and 1520 GMT.
It will then move back to the west-southwest and pass back into the Earth’s shadow.
Image copyright NASA Image caption The moon will move back into the Earth’s shadow on Wednesday
Keep checking back with the BBC as we have full coverage of the eclipse here.