Lunar Eclipse’s Totality

Lunar Eclipse’s Totality

This year promises two total eclipses of the moon – the first visible in parts of the United States in more than three years – beginning on Thursday night, May 15th.

An early summer and late autumn lunar eclipse on tap
Credit: Noel Munford (Palmerston North Astronomical Society, New Zealand)

Total eclipses of the moon occur when the moon passes through the circular shadow that the Earth casts into space and is fully shaded from direct sunlight.

Although masked by the Earth completely or partially from the Sun for as much as an hour and a half, scattering of sunlight off the limbs of our atmosphere doesn’t leave the moon without illumination. Instead the blood-bright color of long-wavelength red light enshrouds the moon’s otherwise familiar grey pallor.

A small scallop of darkness will begin to appear on the moon’s left edge at 10:03 p.m. ET. The moon will take 3 hours and 14 minutes to pass completely through the umbra, and just less than one-third of that time it will be entirely immersed in shadow. The total phase of the eclipse will last 53 minutes beginning at 11:14 p.m. ET. The moon will pass entirely out of Earth’s umbra at 1:17 a.m. ET May 16, and the last evidence of the penumbra should vanish at or around 1:34 a.m. ET.

The next lunar eclipse will be on a Saturday evening, November 8-9, this year, when the moon’s face will again turn an eerie, coppery color. The hue is produced by sunlight filtered, reddened and scattered by the rim of the Earth’s atmosphere. Because of changes in terrestrial dust in the atmosphere, each lunar eclipse is unique in appearance.

The Moon is believed to play an important role in Earth’s habitability . Because the Moon helps stabilize the tilt of the Earth’s rotation, it prevents the Earth from wobbling between climatic extremes. Without the Moon, seasonal shifts would likely outpace even the most adaptable forms of life.

In addition, because our moon is lifeless, it is one of the most appealing places to look for the preserved records of life elsewhere. At least according to recent estimates for the amount of ejected rocks that might survive there, the Moon may hold clues from the early history of Mars, Venus and Earth.

Related Web Pages

Making the Moon
Review of Theories of Moon-Forming Impact (Planetary Science Institute)
Big Bang, New Moon (SwRI)