Skywatchers around the world are gearing up to spot a rare phenomenon, as a lunar eclipse coincides with a supermoon.
A supermoon occurs when the Moon is in the closest part of its orbit to Earth, meaning it appears larger in the sky.
The total lunar eclipse – expected to make the Moon appear red in color – will be visible in North America, South America, West Africa and Western Europe.
NASA claims a supermoon last coincided with a lunar eclipse in 1982 and is not expected to again until 2033.
However, the definition of a supermoon is debated among astronomers.
Skywatchers in the western half of North America, the rest of Europe and Africa, the Middle East and South Asia will see a partial eclipse.
In a total lunar eclipse, the Earth, Sun and Moon are almost exactly in line and the Moon is on the opposite side of the Earth from the Sun.
As the full Moon moves into our planet’s shadow, it dims dramatically but usually remains visible, lit by sunlight that passes through the Earth’s atmosphere.
As this light travels through our planet’s gaseous envelope, the green to violet portions get filtered out more than the red portion, with the result that light reaching the lunar surface is predominantly red in color.
Observers on Earth may see a Moon that is brick-colored, rusty, blood red or sometimes dark grey, depending on terrestrial conditions.
A supermoon occurs when a full or new moon coincides with a Moon that is nearing its minimum distance (perigee) to Earth.
The Moon takes an elliptical orbit around Earth, which means that its average distance changes from as far as 405,000km (its apogee) to as close as 363,000km at the perigee.
The coincidence between a supermoon and an eclipse means that Earth’s lone companion is expected to look 7-8% bigger.
The supermoon should also not be confused with the Moon Illusion, which causes the Moon to appear larger near the horizon than it does higher up in the sky.
The eclipse will begin at 00:11 GMT, when the Moon enters the lightest part of the Earth’s shadow, known as the penumbra, and adopts a yellowish color. At 02:11 GMT the Moon completely enters the umbra – the inner dark corpus of our planet’s shadow.
The point of greatest eclipse occurs at 02:47 GMT, when the Moon is closest to the centre of the umbra. The show will be over by 05:22 GMT on September 28.
Unlike the solar equivalent, a total lunar eclipse event is safe to watch and needs no special equipment.
