Barely a shadow

The first of this year’s four eclipses will flit by like a ghost in the night between March 24 and 25.

(From the “Eclipses” section of Astronomical Calendar 2024.)

The Moon arrives at full phase – opposite to the Sun – more than 21 hours before descending southward across through the ecliptic. So it passes well north of the middle of Earth’s shadow, through the outer region called the penumbra, from within which the Sun is not completely hidden.

Latin paene umbra means “almost shadow” or “scarcely a shadow.” As described in the “Lunar eclipses” section of The Under Standing of Eclipses:

“The penumbra is so light a shadow that it is hardly a shadow at all. Think how brilliant the Sun is: only a speck of it has to show to turn night into day. So it is not surprising that places on the Moon from which most of the Sun is visible look to us undarkened. Only the inner third of the penumbra may be perceptibly gray. Thus penumbral eclipses are hardly even noticed unless and until one edge of the Moon dredges the inner penumbra. Then that edge becomes delicately stained.”

If this eclipse can be seen at all, America is in the grandstand position, facing outward toward the Moon. This also means that the eclipse begins in March 24 by Universal Time and ends in March 25. The central moment, when the Moon is nearest to the middle of Earth’s shadow, happens when the Moon is overhead for the Pacific west of Ecuador.

Go out around midnight at the end of March 25 and with a clear sky you may be able to perceuve that the brilliant full moon is slightly gray at its southern edge.

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