Waning Gibbous Moon: Sixth Lunar Phase Still Shines Even With Lessening Light

Summary: The waning gibbous moon signals lessening light as the sixth lunar phase and appears with Antares and Saturn in March 2015.

waning gibbous moon: NASA Goddard Space Flight Center (NASA Goddard Photo and Video), CC BY 2.0, via Flickr

The waning gibbous moon signals that lunar illumination, as viewed by Earthlings, is decreasing. The waning gibbous moon presents a lunar surface that is more than one-half, or 50 percent, lighted but that is decidedly less aglow than the full illumination of its predecessor, the full moon.

Waning gibbous moon is a perfect descriptive name for this lunar phase. Waning has a definition of "decreasing." Gibbous, derived via Middle English from the Latin word gibbus ("humped"), has a definition of "convex," which describes an outwardly bowed or curved shape.

The waning gibbous moon's decreasing surface illumination, casting a humpbacked shape to the lunar outline in the skies, is clearly discernible. In this phase, the moon's angle with respect to the Earth and the sun measures between 90 and 135 degrees. Less than half of the surface visible to Earthlings is shadowed. More than half of the surface visible to Earthlings is alight.

The waning gibbous moon joins succeeding phases as heralds of decreasing lunar illumination, as viewed by Earthlings. The waning gibbous moon signifies that the moon has passed beyond the halfway point, marked by the full moon, in its orbit around the Earth.

The waning gibbous moon occupies sixth place in the moon's eight-phase monthly lunar cycle. As the sixth phase, the waning gibbous follows the full moon and precedes the Last Quarter Moon.

The eight phases are further reckoned as four primary and four intermediate phases. The waning gibbous moon numbers third in the intermediate phases.

Waning gibbous moons treat viewers with their humpbacked risings and settings. This sixth lunar phase rises after sunset and sets after sunrise. With their early morning blueness, western skies cradle the waning gibbous moon. Between sunset and midnight the waning gibbous moon rules over eastern horizons.

The waning gibbous moon makes its third appearance in 2015 on Saturday, March 7. The humpbacked waning moon reigns until the last quarter moon occurs Friday, March 13, at 1:48 p.m. Eastern Daylight Time (5:48 p.m. Coordinated Universal Time).

The waning gibbous moon's swan song in March 2015 is a stunning trio with ringed-planet Saturn and reddish star Antares. The celestial performance takes place approximately between midnight and dawn. Antares, the ruby heart of Scorpius the Scorpion constellation, shines its orange redness about 8 degrees south of the humpbacked waning moon.

Saturn glows goldenly about 2 degrees southwest of the waning gibbous moon. With its north pole tipped about 25 degrees toward the Earth, Saturn will regale even small telescope viewers with the discernible northern surface of its legendary rings.

As with all lunar phases, the waning gibbous moon offers monthly visual delights for Earthlings.

Things always "look up" (i.e., become better) simply by looking up.

waning gibbous moon at Port Lockroy, northwestern Wiencke Island, Palmer Archipelago, northwestern Antarctica: Liam Quinn, CC BY SA 2.0, via Flickr

Acknowledgment

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

Image credits:

waning gibbous moon: NASA Goddard Space Flight Center (NASA Goddard Photo and Video), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/gsfc/15958998266/

waning gibbous moon at Port Lockroy, Antarctica: Liam Quinn, CC BY SA 2.0, via Flickr @ https://www.flickr.com/photos/liamq/6081560634/

For further information:

Gaherty, Geoff. “Night Sky: Visible Planets, Moon Phases and Events, March 2015.” SPACE.com > Skywatching. March 2, 2015.
Available @ http://www.space.com/16149-night-sky.html

“March Moon and Planet data for March 2015.” Royal Astronomical Society of New Zealand > Solar System.
Available @ http://rasnz.org.nz/SolarSys/

“Moon phase for 12 March 2015 Thursday.” Lunaf.com > Moon phases.
Available @ http://lunaf.com/english/moon-phases/lunar-calendar-2015/03/12/

Sessions, Larry. “Moon near planet Saturn, star Antares before dawn March 12.” EarthSky. March 09–March 15, 2015.
Available @ http://earthsky.org/tonight/predawn-moon-near-saturn-ruby-antares