Printer Friendly

Weird Science: Phases of the Moon

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

The moon appears in many different forms, from a bright white full moon to “half moon” shapes and everything in between. Recall from Activity: Kinesthetic Model of the Sun, the Moon, and the Earth how these different phases are a result of the reflection of sunlight and the position of the sun and moon relative to earth. Also recall that the lunar phases are not caused by the earth’s shadow and are different from lunar eclipses. SF Fig. 6.10 shows the phases of the moon, as viewed from the northern hemisphere.


<p><strong>SF Fig. 6.10.</strong> (<strong>A</strong>) Waxing crescent moon</p><br />
<p><strong>SF Fig. 6.10.</strong> (<strong>B</strong>) First quarter moon</p><br />
<p><strong>SF Fig. 6.10.</strong> (<strong>C</strong>) Waxing gibbous</p><br />

<p><strong>SF Fig. 6.10.</strong> (<strong>D</strong>) Full moon</p><br />
<p><strong>SF Fig. 6.10.</strong> (<strong>E</strong>) Waning gibbous moon</p><br />
<p><strong>SF Fig. 6.10.</strong> (<strong>F</strong>) Third quarter moon</p><br />

<p><strong>SF Fig. 6.10.</strong> (<strong>G</strong>) Waning crescent moon</p><br />

Each lunar month begins inconspicuously with a dark new moon. In the days following the new moon, a thin curving crescent moon begins to appear and grows larger (SF Fig. 6.10 A). The moon is described as waxing as more and more of its near side (the side of the moon facing Earth) becomes illuminated by the sun. From Earth’s northern hemisphere, a waxing moon begins to appear from the viewer’s right-hand side.


As the moon continues to slowly orbit around the earth over the course of a month, the thin waxing crescent moon eventually becomes the first quarter moon (Fig. 6.10 B). From Earth’s northern hemisphere, the waxing first quarter moon appears as a D-shaped half-circle. Quarter moon phases are often inaccurately called a “half moon”, but recall that we cannot see one-half of the moon—the far side—from Earth (for more detail, see Weird Science: Tidally Locked—Why the Man in the Moon Can Always See You.


Even more of the moon’s near side becomes illuminated by sunlight after the first quarter of the lunar month passes, and a convex waxing gibbous moon appears (SF Fig 6.10 C).


Approximately two weeks after the new moon (or more precisely, 14.77 days after), we can see a bright full moon (SF Fig. 6.10 D). The moon is considered to be waning or diminishing in brightness immediately following the full moon. After the full moon, we can observe a waning gibbous moon (SF Fig. 6.10 E), then a third quarter moon (SF Fig. 6.10 F), followed by a waning crescent moon (SF Fig. 6.10 G). From Earth’s northern hemisphere, the waning crescent moon appears as a C-shape.


From Earth’s northern hemisphere, the waxing-to-waning lunar phase series appears in a “D-O-C” order. However, the same moon appears in the opposite “C-O-D” order for lunar observers in the southern hemisphere.

Special Feature Type:

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.