Al Stahler: Moon to suffer eclipse Sunday at sunset | TheUnion.com
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Al Stahler: Moon to suffer eclipse Sunday at sunset

Moonrise from the International Space Station. Light bends when it moves from the vacuum of space into our atmosphere, making the moon look a bit squashed.
Photo by NASA |

Bathed in sunlight, Earth casts a shadow into space. But with nothing out there to catch the shadow there’s no way to see it — usually.

Since the moon was new a week-and-a-half ago, she’s grown to crescent, then to first quarter “D,” now to swollen gibbous.

Sunday evening, the moon will be full. With our backs to the sun, we’ll see the moon lit up, full-face.



Full moon occurs when sun, Earth and moon are in syzygy (SIH-zih-gee): when they line up.

But the line-up is not usually precise. A line from sun to Earth, extending outward, will usually miss the moon.




Sunday evening, however, the line will hit the moon, and the moon will slip into Earth’s shadow. This will cause the moon to suffer a total eclipse. (Some thousands of years ago, astronomy and astrology were practiced by the same people. Astronomy still retains a little spookiness in its vocabulary). The moon’s orbit also plays a part in causing an eclipse.

The moon’s orbit around Earth is not a perfect circle — sometimes the moon is closer, sometimes the moon is farther away.

When she was new, the moon was within pocket change of a quarter-million miles away from Earth.

Since then, she’s been coming closer.

This Sunday evening, the full moon will be 30,000 miles closer than when she was new.

When something is closer, it looks bigger — those 30,000 miles will make a noticeable difference.

Added to her proximity, there’s also the “moon illusion.”

For some reason, when the moon — or anything else — is just above the horizon, our brains tell us it’s bigger than it really is. No physics here — it’s all in our heads.

Deep within Earth’s shadow, the moon, by rights, should see no sunlight.

But just as light bends when it moves from water to air (making a spoon in a half-glass of water look bent), light bends when it moves from air to vacuum.

Sunlight, passing though the atmosphere edging our planet — passing through all of Earth’s “rosy-fingered” dawns and dusks — will bend into Earth’s shadow, and color the moon a ruddy sunrise/sunset-red.

Just how red depends on what’s in the air; volcanic dust, road dust, farm dust, sea spray, for example.

No telescope is needed to enjoy the eclipse, nor any eye protection — the naked eye works great.

The moon will enter Earth’s shadow, Sunday evening, just after 6 p.m. — but it won’t rise above the horizon for another half-hour.

The moon will rise, therefore, partially eclipsed. As the moon rises higher, the eclipse will grow deeper.

Totality begins at 7:11 p.m., and lasts until 8:27; it’ll then take another hour for the moon to escape Earth’s shadow completely, back into full sunlight.

Al Stahler’s science programs can be heard on KVMR (89.5 FM). He brings an enjoyment of science and nature to students of all ages and may be reached at stahler@kvmr.org.


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