Full moon shone Monday morning in cloudless sky over D.C.

The cloudless skies that covered the District on Sunday remained cloudless in the first hours after midnight Monday, permitting an unobstructed view of the moon as for the third time this year it became full.

The moment of maximum roundness occurred at 3 a.m. At at that hour the night sky was clear, with not a cloud seeming to float above Washington to obscure the view.

Aside from such mundane matters as the call of sleep, or the lack of a good view to the south, nothing in Washington’s environment seemed to prevent the sight of the moon at that key moment in its monthly cycle.

However, students of the skies note that despite the lack of clouds, the moon did fall short for a time Monday morning of the maximum brightness of which it is capable.

That is because the moon shines by reflecting the light that falls upon its face from the sun. On Monday morning that light was diminished for a time, as a result of the path taken by the moon around Earth.

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That path took the moon close to the core of the shadow cast by Earth across space. Sunlight does not reach inside that core shadow. If all or part of the moon passes through it, all or part of the moon goes dark, in a lunar eclipse.

But outside that core shadow, surrounding it like a kind of halo, is an area of partial shadow. When all or part of the moon passes through the partial shadow, it is dimmed; it still receives sunlight, but less than usual, and that, according to the specialists, is what occurred Monday morning. It is called a penumbral eclipse, meaning that the moon passed through Earth’s penumbra, or partial shadow.

It is possible with the unaided eye to detect this faint decline in brightness, specialists say. But it is not easy, they said. In addition, a temperature of 40 degrees in Washington may have been chilly enough to discourage intensive observation.

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Aside from that, Monday seemed a fine early spring day in Washington, As the morning went on, the temperature fell four degrees from its 3 a.m. figure, reaching a low of 36. That was five degrees below the average low for March 25.

From there it rose to a high of 57, which was three degrees below the average high for the date.

It was a cool early spring day, but it remained a day of relatively few clouds. The same clear skies that allowed a look at the full moon at 3 a.m. appeared bright and blue hours later when the sun rose.

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