BBC News

Total lunar eclipse to meet 'supermoon'

By Paul Rincon
Science editor, BBC News website

image copyrightAFP
image captionThis will be the second total lunar eclipse this year

The Moon will turn a rusty hue in the early hours of Monday and may seem larger in the sky.

The event is caused by a total lunar eclipse coinciding with another astronomical event called a supermoon.

It's the second total lunar eclipse this year, but the first since 2008 where the whole eclipse will be visible from the UK.

The entire eclipse will be visible from eastern North America, South America, West Africa and western Europe.

Skywatchers in the western half of North America, the rest of Europe and Africa, the Middle East and South Asia will see a partial one.

From the UK, observers will see the Moon pass through the Earth's shadow in the early hours of Monday morning. In North and South America the eclipse will be seen on Sunday evening.

image copyrightNASA

Eclipse facts

  • The last time a total lunar eclipse was visible in its entirety from the UK was 2008; the next time one will be visible after this is in 2019
  • The supermoon, where Earth's satellite is near its minimum distance from our planet, means that the Moon will appear 7-8% larger in the sky.
  • The moon may look rust-coloured during a total lunar eclipse - giving rise to its nickname Blood Moon. This is because the Earth's atmosphere scatters blue light more strongly than red light, and it is this red light that reaches the lunar surface
  • During the eclipse, the Moon lies in front of the stars of the constellation Pisces

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 colour.

Observers on Earth may see a Moon that is brick-coloured, rusty, blood red or sometimes dark grey, depending on terrestrial conditions.

Dr Robert Massey, deputy executive director of the UK's Royal Astronomical Society, told BBC News that the eclipse is an "incredibly beautiful event".

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. But Dr Massey added: "The definition of 'supermoon' is slightly problematic.

"Is a supermoon taking place at the perigee, the day before, the day after? Does a supermoon have to be a particularly close perigee, or can it be a bit further out? It's not very well defined."

He said a supermoon was to some extent a moveable feast compared with an eclipse, where the timing can be measured precisely.

As a result, Dr Massey explained, claims of the extreme rarity of a supermoon coinciding with an eclipse were overstated.

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 start at 01:11 BST, when the Moon enters the lightest part of the Earth's shadow, known as the penumbra, and adopts a yellowish colour. At 03:11 BST, the Moon completely enters the umbra - the inner dark corpus of our planet's shadow.

The point of greatest eclipse occurs at 03:47 BST, when the Moon is closest to the centre of the umbra. The sky show is over by 05:22 in the morning on Monday.

The Royal Astronomical Society says that unlike the solar equivalent, a total lunar eclipse event is safe to watch and needs no special equipment.

The next total lunar eclipse visible in its entirety from the UK will be in 2019.

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