A sight for sore eyes: Supermoon comes a little closer

Skygazers last night witnessed a spectacular sight as the biggest moon seen in 68 years rose in the Irish sky.
A sight for sore eyes: Supermoon comes a little closer

However, Astronomy Ireland chairman David Moore sought to reassure people yesterday that this was no supernatural event but rather an optical illusion.

Cloud cover denied many others the chance to enjoy the rare lunar experience of a ‘supermoon’, but Mr Moore said tonight would present a further opportunity to view the magnified moon phenomenon.

Officially known as a perigee moon, the rare effect occurs when a full moon coincides with the orbit of the moon at its closest point to Earth.

“The moon’s orbit is what is doing this, and it just happens to coincide being at its closest, because the moon is not in a perfectly circular orbit, at the same time that there is a full moon,” said Mr Moore.

The moon rises behind the castle of Almodovar in Cordoba, southern Spain. Usually the moon is 384,400km away from Earth, on average. At its closest point last night, the supermoon was 351,825km away. Picture: Miguel Morenatti
The moon rises behind the castle of Almodovar in Cordoba, southern Spain. Usually the moon is 384,400km away from Earth, on average. At its closest point last night, the supermoon was 351,825km away. Picture: Miguel Morenatti

“It’s a few kilometres closer than it has been other times; all these perigee moons are roughly the same size so we have this incredible record for Science Week, the closest for 68 years.”

The last time the phenomenon was visible was 1948 — and it will not be matched again for possibly another 18 years, in 2034.

The moon has a slightly elliptical orbit, meaning its distance from Earth can vary.

Usually the moon is 384,400km away, on average.

The supermoon over Dublin city last night. Picture: Naoise Culhane
The supermoon over Dublin city last night. Picture: Naoise Culhane

At its closest point last night, the supermoon was 351,825km away from Ireland, according to Mr Moore.

“It’s about 400,000km on average and the Earth is about 13,000km wide, so where you are on the Earth can actually affect this record,” he said.

“And we’ve done the calculations for Ireland and the exact distance is 351,825km.”

The supermoon led to the moon appearing 30% brighter and 14% closer last night.

Although the moon appeared bigger, this was just an optical illusion, said Mr Moore.

The supermoon seen through the eye of a Celtic Cross in Aghadoe Cemetery, Killarney. Picture: Don MacMonagle
The supermoon seen through the eye of a Celtic Cross in Aghadoe Cemetery, Killarney. Picture: Don MacMonagle

“Like all these optical illusions, no one is really certain why it happens but the human-eye brain combination seems to just scale things up and the moon looks very big,” said Mr Moore. “I’ve seen it many times myself.

“We know it’s not — you can measure it with scientific instruments.

“It’s exactly the same size as normal, it’s not the extra air magnifying the effect or anything like that. It’s a purely psychological effect.”

Mr Moore said that if clouds blocked your view last night, the brightness and the closeness of the moon should be visable tonight.

“We take a 32-county view of the phenomenon, from sunrise to sunset, we know the moon will be in view with breaks in the clouds,” he said.

Astronomy Ireland is holding a competition for the best photographs of the supermoon taken both last night and tonight.

Images can be emailed to magazine@astronomy.ie with the winning entry being featured in Astronomy Ireland .

Meanwhile, Science Week is running nationally until November 20.

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