Supermoon evokes enthusiasm from Washington-area skywatchers

A few minutes after midnight on Monday morning in Washington, with the bright full moon almost directly overhead, it seemed necessary to stake out a position somewhere between those who scoffed at the idea of a “supermoon,” and those who marveled at the sight of it.

This was the first, last and only supermoon of 2017. The title is bestowed when the moon becomes full at the time of its closest approach to Earth on a given orbit.

When full, the moon is obviously brighter than when part of it lies in shadow. And it is not knowledge of astronomy so much as common sense that ordains that a moon that is closer to the earth is a moon that is brighter.

So when the brightness of a full moon coincides with the brightness of a closer-than-usual moon, why not call it a “supermoon”?

Well the debate, such as it is, entails appreciation of the numbers involved. How much larger does the moon appear when it is at its closest point of approach? How much brighter is a full moon when seen as it makes a close approach on its orbit.

It is not so much a question of the actual amounts. Those can be measured, and most people seem likely to accept them. The moon on Sunday has been described as appearing about 7 percent larger, as a result of its proximity.

And a moon with a diameter about 7 percent larger, should appear about 14 percent brighter. The brightness will depend on the moon’s illuminated area. That depends on the square of its radius.

Even if a 7 percent increase in radius or diameter is perhaps hard to spot, can a 14 percent increase in brightness be detected with the naked eye?

Some would probably say yes. Others might be less confident. Some subjectivity is inevitably involved.

Several people posted their responses on Twitter Sunday night. They seemed to be impressed by the supermoon. Perhaps this was at least in part because they had seen the moon relatively soon after it began to rise.

The moon looks larger when lower.

A tweet posted under the name Donna Claycomb Sokol seemed unequivocal.

“Stop whatever you’re doing,” it read, “and please go outside to see the moon.

“It’s magnificent.”

In another tweet, this one appearing under the name of Alana Alsop, was clear and succinct in its appraisal of the lunar spectacle. “Georgeous,” it read.

Another tweet, posted under the name Dionisios Favatas described the supermoon as “brightening up skies.”

In addition, the tweet indicated that the sight might have value beyond the merely esthetic.

“Something to distract us from all the political news,” it read.

Still another tweet wryly demonstrated the moon’s ability to stimulate the imagination.

In a tweet published under the name of Jacob Harris, a tongue-in-cheek warning was issued: “Remember that a supermoon means superwerewolves.” it said.”Be careful tonight.”

Anyone who missed Sunday night’s supermoon can see a fairly similar replay on Monday night, experts said.

Meanwhile, as seen above K Street early Monday morning, the moon may not have appeared that much bigger than usual. However it was bright. If you knew nothing about any supermoon, you might have wondered how they increased the brightness.

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