For an existential instant, the 12th full moon of the year will reach fullness at 12:12 a.m. on 12-12 (that would be Thursday).

Arguably, that would be the last full moon of the decade, although calendar purists would strongly object.

It is also known as the “Cold Moon" for obvious reasons, and it will be a particularly cold moon overnight as temperatures tumble into the 20s around the Philadelphia area.

The moon will rise around sunset Wednesday, and when it reaches the moment of fullness, it will be burning bright under what the National Weather Service promises will be completely clear skies, casting impressive shadows and illuminating any snow that survives the day.

The moon is ever-restlessly waxing and waning, and isn’t full for long, notes Brian Lada, a meteorologist and sky enthusiast at AccuWeather Inc.: Blink, and you’ll miss it.

“It’s really at that one precise instant,” he said. Lada says for moonlight he prefers the night before fullness, when the moon rises earlier and thus peaks while most people are still awake.

He had posted an item on the AccuWeather site that described it as the last full moon of the decade, but is aware that not everyone would agree.

Can a decade begin in a “00” year? Lada agreed that would constitute a paradox: “There is no year zero.” So shouldn’t the decades and centuries begin with the 01 year?

This has been a centuries-old debate, and a Library of Congress researcher found 200 pamphlets, dating to the 17th century, that address this mighty human dilemma.

The purists might well be right, but the court of public opinion has decidedly ruled against them.