Eclipse Will Darken 69% of Moon’s Surface Sunday

Southern Californians with a clear view of the southeastern horizon will have the opportunity to view a partial eclipse of the moon shortly after sunset Sunday.

The eclipse will block 69% of the moon’s surface when it reaches its maximum at 9:57 p.m. PDT, about halfway through the three-hour, easily visible portion of the eclipse. Weather permitting, the phenomenon will be visible from most areas of North, South and Central America.

Lunar eclipses occur when the Earth comes between the sun and the moon, and the sun casts the Earth’s shadow on the moon. In this case, the Earth is not in a direct line between the two celestial bodies, so only part of the moon falls in shadow.

The eclipse takes place in three stages--with two dim “penumbral” stages sandwiching a darker “umbral” stage. The umbra is the dark central portion of the Earth’s shadow where light from the sun is cut off. The penumbra is the larger region surrounding the umbra where only part of the light is cut off.

The moon will enter the penumbra at 7:09 p.m., 50 minutes before the moon rises over California. Because the shadow is so light, however, the moon will look like a normal full moon to most observers when it rises Sunday at 7:59. It will begin to pass into the umbra at 8:27 p.m.

At 11:27 p.m., the moon will pass out of the umbra. It will remain in the penumbra for another 87 minutes.

Red sunlight filtering through the Earth’s atmosphere during the eclipse might turn the moon a reddish color.

The spectacle will be easily visible with the naked eye, but binoculars “will do wonders with the moon for this eclipse,” said Leif Robinson, editor of Sky & Telescope magazine.

Unlike an eclipse of the sun, “you don’t have to worry about any special eye safety precautions” during the lunar eclipse, said Alan Dyer, an editor at Astronomy magazine. “The moon is perfectly safe to look at.”