2016 Almost Lunar Eclipse Shadowlessly Taps Earth’s Penumbra Aug. 18

Summary: Earth's penumbra is expected to cast no noticeable shadow across the moon's face during the 2016 almost lunar eclipse Thursday, Aug. 18.

2016's almost lunar eclipse: Tom Ruen (SockPuppetForTomRuen), Public Domain, via Wikimedia Commons

The seemingly shadowless 2016 almost lunar eclipse slated to occur in the United States before sunrise Thursday, Aug. 18, is a type of penumbral lunar eclipse. The almost lunar eclipse begins at 9:42:32 a.m. Coordinated Universal Time (UTC), which is 5:42 a.m. Eastern Daylight Time.

The ephemeral almost lunar eclipse’s tapping of the northern edges of the earthly penumbra will last about 18 minutes.

During the 2016 almost lunar eclipse, the full moon will be above the horizon over most of the Pacific Ocean and the western Atlantic Ocean. The geographic region of visibility also includes much of Antarctica, most of Australia, most of Japan and the Russian Far East, all of Alaska and the United States’ Lower 48, and much of Canada.

A lunar eclipse is occasioned by the straight-line alignment of moon, Earth and sun that characterizes the moon’s full phase as well as the alignment of the lunar orbit with the plane of the Earth and the sun. Earth’s intervening position between the moon and the sun affects the path of direct sunlight and casts cones of darker and lighter shadows across the lunar orbit.

An almost lunar eclipse occurs when the moon’s position barely taps the faint, outer part of Earth’s shadow, known as the penumbra (Latin: paene “almost” + umbra “shadow”). Any shadows sourced from the penumbra are so faint and slight that they generally are virtually undetectable by Earthlings.

The full moon that grazes Earth’s penumbra looks exactly like a normal, uneclipsed full moon. The seeming lack of differentiation explains a penumbral eclipse’s other descriptive name of an almost lunar eclipse.

Thursday’s almost lunar eclipse has additional significance as the closer of Saros 109. An almost lunar eclipse in the year 736 opened Saros 109. Originating as a system for predicting lunar eclipses, the Saros cycle also applies to determining solar eclipses.

The Saros cycle is a system dating back to the Chaldeans of the eastern Mediterranean, a small Semitic nation described as “bitter and swift” in the Old Testament’s Book of Habakkuk (1:6). A Saros cycle encompasses a period of approximately 18 years 11 days 8 hours (6,585.3 days).

An almost lunar eclipse is one of the three types of eclipses experienced by the moon from the perspective of Earthlings. The other two lunar eclipses appear as partial or as total obscuring of the visible lunar surface.

The next lunar eclipse in 2016 will occur next month, Friday, Sept. 16, or Saturday, Sept. 17, depending upon global location. September’s lunar eclipse will involve Earth’s penumbra again. The moon’s orbit will not skim the outermost penumbral edges, so ecliptic shadows will be noticeable.

The geographic region of eclipse visibility for September’s eclipse encompasses a wide swatch from the central Antarctic Ocean eastward to the central Pacific Ocean and includes most of the Antarctic and Arctic land and water regions. September’s penumbral eclipse will be visible over the continental entirety of Africa, Asia, Australia and Europe. Easternmost Greenland and Iceland as well as Brazil’s eastern bulge will enjoy visibility.

Thursday morning’s moon may appear to the casual observer as just another brightly shining full moon. Although Aug. 18’s full moon will not look like an eclipsed moon, it nevertheless offers the tantalizing attraction of being far more than what it seems.

2016 almost lunar eclipse path, as viewed from center of moon during the greatest eclipse: Tom Ruen (SockPuppetForTomRuen), Public Domain, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

2016's almost lunar eclipse: Tom Ruen (SockPuppetForTomRuen), Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Lunar_eclipse_chart_close-2016Aug18.png

2016 almost lunar eclipse path as viewed from center of moon during the greatest eclipse: Tom Ruen (SockPuppetForTomRuen), Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Lunar_eclipse_from_moon-2016Aug18.png

For further information:

“August 18, 2016 – Almost Lunar Eclipse.” Time and Date > Sun & Moon > Eclipses.
Available @ http://www.timeanddate.com/eclipse/lunar/2016-august-18

Byrd, Deborah. "What is a penumbral eclipse of the moon?" EarthSky > Space. Oct. 17, 2013.
Available @ http://earthsky.org/space/what-is-a-penumbral-eclipse-of-the-moon

Espenak, Fred. "Eclipses and the Saros." NASA Eclipse Web Site. Last updated Jan. 12, 2012.
Available @ http://eclipse.gsfc.nasa.gov/SEsaros/SEsaros.html

Lada, Brian. "Thursday's full moon: The lunar eclipse that no one will notice." AccuWeather > Blogs. Aug. 15, 2016.
Available @ http://www.accuweather.com/en/weather-blogs/astronomy/thursdays-full-moon-the-lunar-eclipse-that-no-one-will-notice/59494660

"Lunar Saros 109." Wikiwand.
Available @ http://www.wikiwand.com/en/Lunar_Saros_109

"What is a Penumbral Lunar Eclipse?" Time and Date > Sun & Moon > Eclipses > Lunar Penumbral.
Available @ http://www.timeanddate.com/eclipse/penumbral-lunar-eclipse.html

"What are eclipses?" Time and Date > Sun & Moon > Eclipses > Solar and Lunar.
Available @ http://www.timeanddate.com/eclipse/eclipse-information.html#Lunareclipses