If last night’s blood supermoon didn’t appear as the giant, bright-red orb you might have expected, that wasn’t your just your eyesight playing up.
Astronomer Dr Grant Christie said the rare combination of the supermoon and a total lunar eclipse looked just as it was supposed to – even though some might have been puzzled at the moon’s colouring, or a slither of light around its edges.
“You only really get that deep red effect when it’s in totality – and it only barely just got into totality,” he said.
Blood moons – also known as total lunar eclipses – occur when the Earth lines up between the Moon and the Sun.
This hid the Moon from sunlight and blocked most of the blue light, with the remaining light refracting onto the Moon’s surface and causing a red glow.
Last night, the period of “totality” where the Moon was completely hidden from the Sun by Earth – and when the reddening was most noticeable – lasted around 14 minutes from 11.11pm.
“So there was a pinkish tinge to it, or a sort of ochre colour, and that was more or less what I expected,” Christie said.
“And when you get that deep red, it’s never going to be fire-engine red, but a deep maroon colour.”
This colour appeared most noticeably when the moon was entirely in the middle of the Earth’s shadow.
“We were quite a long way off the middle [of the shadow] but that was about as close as you could get to the edge of the thing and still call it a total eclipse.
“So it’s not like a cartoon, where you’re inside that circle of totality that’s all uniform.
“That’s because the circle has a gradation of absorption, which meant there was a little bit of light leaking in that gave it a blurry edge.
“The redder bits were those furtherest away from the edge of the shadow. So if you can imagine the moon being moved over to the middle, the red would have been more noticeable and the moon would have looked fainter, due to more absorption.
“In last night’s case, there was still some scattered light hitting the Moon’s surface, even though it was technically a total eclipse.”
He said that tinge wouldn’t have looked any different to anywhere else on the dark side of Earth.
“Just in our case, it was higher in the sky, as we were somewhere near the middle of the Earth, as seen from the moon,” he said.
“There were lots of other places where the eclipse only occurred just above the horizon – and they would got lots of other effects due to the colouring effects of their local atmosphere.
“Here, for instance, when the moon is on the horizon you’re looking at about 10 times more atmosphere than you are when it’s straight above your head.”
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