Last Quarter Moon in the Homestretch as Seventh of Eight Phase Lunar Cycle

Summary: The last quarter moon, which is seventh in the eight-phase lunar cycle, claims two successive Friday the 13ths in 2015, with the second in March.

Last Quarter Moon: March 10, 1969 image by Apollo 9 Crew ~ Apollo 9 Crew, CC BY 2.0, via Earth Science and Remote Sensing Unit, NASA Johnson Space Center

The last quarter moon numbers as the seventh phase in the moon's monthly eight-phase lunar cycle. The cycle is further divided into four primary and four intermediate phases. The last quarter moon stands as the fourth and final primary phase.

The last quarter moon signals that the moon is in the homestretch of its cyclical journey, with the next cycle's new moon about seven days away. In this phase, the moon is three-fourths of the way through its orbit around the Earth.

The moon begins the last quarter phase by forming a 90 degree angle with the sun, steadily decreasing the angle during this phase to almost 45 degrees. At 45 degrees, the waning crescent moon takes over as the fourth and last intermediate phase and also as the eighth and final phase of the total cycle.

With completion of the monthly lunar cycle by the appearance of the waning crescent moon, the cycle begins anew with the new moon as the moon commences another orbit around the Earth.

As the moon progresses further in its orbit, its risings lag behind solar sunrises, falling behind by about 50 minutes with each day. By the last quarter, the moon rises for Earthlings about 18 hours after sunrise, or, six hours before the next day's sunrise.

The last quarter moon prettifies the skies from midnight to noon. This phase rises around midnight and sets around noon. The last quarter moon's zenith, its highest appearance in the sky, is logged at dawn.

The last quarter moon continues the decrease in illumination of the lunar surface that began with its predecessor, the waning gibbous moon. The lunar surface of the last quarter moon appears as half-lit, at 50 percent. In the Northern Hemisphere, the left side appears as the illuminated half. In the Southern Hemisphere, the right side is lit.

The last quarter moon makes its third appearance in 2015 on Friday, March 13th, occurring at 1:48 p.m. Eastern Daylight Time, or 5:48 p.m. Coordinated Universal Time.

The last quarter moon claims two of the three Friday the 13ths that occur in 2015. The year's first Friday the 13th happened in February and coincided with the year's second appearance of the last quarter moon. The year's third and last Friday the 13th shows up in November and claims the waxing crescent moon as the day's lunar phase.

The last quarter moon yields to its successor, the waning crescent moon, on Sunday, March 15.

"The Last Quarter Moon rises at midnight": Mats Bjorklund, CC BY 3.0 AU, via Museum Victoria

Acknowledgment

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

Image credits:

last quarter moon at 21:50:00 GMT on March 10, 1969: Apollo 9 Crew, CC BY 2.0, via Earth Science and Remote Sensing Unit, NASA Johnson Space Center @ http://eol.jsc.nasa.gov/SearchPhotos/photo.pl?mission=AS09&roll=23&frame=3500

The last quarter moon rises at midnight: Mats Bjorklund, CC BY 3.0 AU, via Museum Victoria @ http://museumvictoria.com.au/education/learning-lab/little-science/teacher-guide/phases-of-the-moon/

For further information:

Byrd, Deborah. “Understanding last quarter moon.” EarthSky > Tonight > Moon Phases. July 10, 2012.
Available @ http://earthsky.org/moon-phases/last-quarter

Enevoldsen, Alide. “Skies Over West Seattle, March 2015: Seeing stars (and planets); lunar eclipse ahead.” West Seattle Blog. March 8, 2015.
Available @ http://westseattleblog.com/2015/03/skies-over-west-seattle-march-2015-seeing-stars-and-planets-lunar-eclipse-ahead/

Fuller, David. “Moon Maps.” Eyes on the Sky > Moon.
Available @ http://www.eyesonthesky.com/Moon.aspx

“Names and images of the 8 moon phases.” MoonPhases.info > Moon Phases.
Available @ http://www.moonphases.info/moon_phases.html

"What Is the Moon Doing?" Astronomy Group / University of St. Andrews > Fiona Vincent > What's in the sky? > Moon general.
Available @ http://star-www.st-and.ac.uk/~fv/sky/moon-general.html