"Total" Penumbral Lunar Eclipse - March 14

An unusual “Total” Penumbral Lunar Eclipse will occur during the night of 2006 MAR 14/15. The penumbra is the outer fringe shadow of the earth. At mid-eclipse the Moon will be fully immersed in the penumbra and not at all in the dark inner shadow called the umbra. At that moment anyone standing anywhere on the half of the Moon’s surface facing Earth would be observing a partial occultation of the Sun by the Earth. Those of us on the nighttime portion of the Earth will notice that the area around one limb (edge) of the Full Moon has darkened. The Moon’s magnitude in the penumbra will be +1.027 and in the umbra will be –0.066, meaning it will miss the umbra by 0.066 lunar diameters.

The last such TPLE occurred in 1999, but the next one following this month’s event will be in 2053. In fact only one occurs in each of the periods 1666-1899 and 2158-2428.

2006 MAR 14/15

21:24 UT Moon Enters Penumbra
23:48 UT Maximum Eclipse
02:11 UT Moon Exits Penumbra

My calculations employ the “French rule” and account for the oblate shape of the Earth. To see a graphic that I created demonstrating the event, click: http://www.curtrenz.com/astronomical.html

At least one media source is reporting that the next penumbral lunar eclipse after this month’s event will occur in 2053. That’s only true for “Total” Penumbral Lunar Eclipses. Actually, penumbrals occur fairly frequently. There will be three in 2009, but none a TPLE. And every total or partial lunar eclipse is preceded and followed by penumbral stages.

Despite the fact that after this month’s TPLE the next will be in 2053, we are nevertheless living in a rich period for such events. There exists a cycle of roughly 565 years for many factors involving both solar and lunar eclipses. There are no TPLE’s during the periods 1666-1805 and 2223-2428. There were 10 such events during the period 1900-1999. During this century they will occur in 2006, 2053, 2070, 2082 and 2099. We’re also living in a rich period for total lunar eclipses, including groupings of four of them known as tetrads as we had in 2003-4 and will again in 2014-5.

A penumbral eclipse is not a spectacular event. For many of them the slight darkening of the Full Moon goes unnoticed. However, when the Moon’s limb gets within about 30% of a lunar diameter from the Earth’s umbra, a dimming on the side near the umbra can be perceived. That will definitely be the case this month when the Moon misses the umbra by about 7% of a lunar diameter.

GLOSSARY:

Umbra - The Earth’s umbra is the dark portion of its shadow. An observer standing in the umbra would not be able to see any portion of the surface of the Sun since it would be completely obscured by the Earth.

Penumbra – The Earth’s penumbra is the outer gray fringe shadow surrounding the umbra. An observer standing in the penumbra would see the Sun being partially obscured by the Earth.