Waxing Gibbous Moon: Fourth of Eight Phases in Monthly Lunar Cycle

Summary: As the fourth of the moon's eight phases, the waxing gibbous moon precedes the moon's brightest phase, the full moon.

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

For Earthlings, a lunar cycle travels through eight phases, beginning with the new moon and ending with the last quarter moon. Waxing gibbous moon designates the fourth phase in the moon's eight-phase cycle. Waxing gibbous is preceded by the third phase, the first quarter moon, and followed by the fifth phase, the full moon.

The eight phases are further broken down into four primary phases and four intermediate phases. Waxing crescent moon initiates the first intermediate phase by serving as the transition from the first primary phase, the new moon, to the second primary phase, the first quarter moon.

Waxing gibbous moon is identified as the second intermediate phase. The waxing gibbous moon serves as the transition from the second primary phase, the first quarter moon, and the third primary phase, the full moon.

As an intermediary between the first quarter moon and the full moon, the waxing gibbous moon signals the passage from partial to full lunar illumination. The first quarter moon presents a view of 50 percent illumination of the lunar surface to Earthlings. The waxing gibbous moon presents a view of more than 50 percent -- but less than 100 percent -- illumination of the lunar surface to Earthlings. The full moon presents a view of complete illumination of the lunar surface to Earthlings.

Waxing gibbous moon is an accurate descriptive name. Waxing is a verb form ending in -ing that may be used as an adjective. One of the definitions of waxing is "increasing," which refers in the lunar cycle to increasing illumination of the Moon's surface as viewed by Earthlings.

In the lunar cycle, gibbous refers to the bulging curve of illumination, outlining a humpbacked shape, which covers more than half of the lunar surface viewable to Earthlings. Gibbous is a Middle English word derived from gibbus, the Latin word for "humped." Gibbous has the definition of "convex," which means "bowed or curved outward."

The waxing gibbous moon rises in the hours between noon and sunset and sets in the early morning hours after midnight. The waxing gibbous moon often may be seen in the afternoon, well before sunset, because of the moon's increasing distance from the Sun. The waxing gibbous moon's journey in the lunar orbit around the Earth traces the sector between the 90-degree angle formed by the first quarter moon with the sun and the 180-degree angle formed by the full moon with the sun.

Although skygazers are regaled by the difficult-to-miss full moon, other phases, such as the waxing gibbous moon, provide beauty and interest as well.

waxing gibbous moon over Roses, Catalonia, northeastern Spain: Dennis van Zuijlekom (dvanzuijlekom), 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:

waxing gibbous moon: NASA Goddard Space Flight Center (NASA Goddard Photo and Video), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/gsfc/15984099212/

waxing gibbous moon over Roses, Catalonia, northwestern Spain: Dennis van Zuijlekom (dvanzuijlekom), CC BY SA 2.0, via Flickr @ https://www.flickr.com/photos/dvanzuijlekom/15419696882/