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Darin Oswald/PA Images
January's blood moon viewed from Idaho in the United States.
# the bloodening
Tonight's blood moon is the longest of the 21st century - here's when you can see it best
The lunar eclipse coincides with a close passing of Mars in tonight’s sky.
THE LONGEST ‘BLOOD moon’ eclipse this century will coincide with Mars’ closest approach in 15 years tonight, to offer skygazers a thrilling astronomical double bill.
Viewers will need no protective eye gear to observe the spectacle — unlike when watching solar eclipse.
For about half the world, the moon will be partly or fully in Earth’s shadow from 6.14 pm to 12.28 am (Irish time) tomorrow morning, six hours and 14 minutes in all.
In Ireland, the eclipse will last for about 3 hours and 6 minutes, from 9.22 pm to 12.28 am.
The period of complete eclipse — known as “totality”, when the moon appears darkest — will last for just under 51 minutes in Ireland, from 9.26 pm to 10.13 pm.
In some parts of the world, totality will last for 103 minutes, making it the longest eclipse of the 21st century
Unfortunately, clouds in some parts of Ireland could hurt the chances of seeing the phenomenon.
Blood Moon
A total lunar eclipse happens when Earth takes position in a straight line between the moon and sun, blotting out the direct sunlight that normally makes our satellite glow whitish-yellow.
The moon travels to a similar position every month, but the tilt of its orbit means it normally passes above or below the Earth’s shadow — so most months we have a full moon without an eclipse.
When the three celestial bodies are perfectly lined up, however, the Earth’s atmosphere scatters blue light from the sun while refracting or bending red light onto the moon, usually giving it a rosy blush.
This is what gives the phenomenon the name “blood moon”, though Mark Bailey of the Armagh Observatory in Northern Ireland said the colour can vary greatly.
It depends partly on “how cloudy or transparent those parts of the Earth’s atmosphere are which enable sunlight to reach the moon”, he told AFP.
“During a very dark eclipse the moon may be almost invisible.
“Less dark eclipses may show the moon as dark grey or brown… as rust-coloured, brick-red, or, if very bright, copper-red or orange.”
The long duration of this eclipse is partly due to the fact that the moon will make a near-central passage through Earth’s umbra — the darkest, most central part of the shadow.
Our constant companion will also be at the farthest point on its orbit from Earth, making its movement across the sky slower from our perspective, thus spending longer in the dark.
Mars
At the same time, Mars will hover near the moon in the night sky, easily visible with the naked eye.
Our neighbouring planet will appear unusually large and bright, a mere 57.7 million kilometres from Earth on its elliptical orbit around the sun.
“We have a rare and interesting conjunction of phenomena,” said Pascal Descamps, an astronomer with the Paris Observatory.
“We should have a coppery red tint on the moon with Mars the ‘Red Planet’ just next to it, very bright and with a slight orange hue itself.”
© – AFP 2018 with reporting by Rónán Duffy
