Tuesday, December 21, 2010

Selene

Up a good part of the night for the total lunar eclipse. The Bahamas had a ringside seat, with the eclipse taking place high overhead. The disadvantage: The show took place between 1:30 and 5:00 AM, with mid-totality at 3:15.

We stepped out onto the porch as the partial phase was scheduled to begin. Ouch! The sky mostly covered with scudding clouds, only glimpses of the Moon through occasional gaps. We persisted. By the time the Moon was half in shadow the sky was clearing. As totality began not a whiff of haze in the sky.

And there was the Moon, drifting high overhead like a tangerine-colored balloon, in the midst of the brilliant winter constellations -- Taurus, Orion, Gemini, Auriga. The jewel in the crown. Dazzling!

As the Earth circles the Sun, the tip of its rapier-like shadow sweeps across the starry sky at about a degree a day (a degree is about twice the width of your little finger held at arm's length). The Moon moves across the stars at about a degree every two hours. As we watched, the Moon overtook the moving shadow and plunged into the tinted gloom. A bit over an hour later it nosed out of the other side of the shadow and raced on ahead, recovering its full-moon status.

It was a bright eclipse, by my estimation an L=4 on the brightness scale. The light that illuminates the Moon during totality is bent into the shadow by the Earth's atmosphere. How much light falls on the fully-eclipsed Moon and its color is greatly dependent on conditions in the atmosphere and difficult to predict. A fully-eclipsed Moon can range from almost invisible to last night's dusky orange.

More on the aesthetic experience tomorrow.