Staar Moon Phases Science Worksheets printable pdf download

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STAAR Science Tutorial 28

TEK 8.7B: Moon Phases

TEK 8.7B: Demonstrate and predict the sequence of events in the lunar cycle.

At any point in time, half of the Moon is lit (illuminated) by the Sun, and half is not lit.

However, for a viewer on Earth at any given time, the Moon may appear to be

completely lit, completely dark, or somewhere in between. These varying appearances

of the Moon are known as “Moon Phases,” and have been used by humans for thousands

of years to keep track of time, even before calendars were invented. It takes 29.5 days

for the Moon to cycle through all of its phases, and return to the same starting point.

Our current calendar system used this fact to establish months of about 30 days.

The Moon takes about 27.3 days to orbit (revolve) once around the Earth. It takes the

same amount of time, 27.3 days, for the Moon to spin (rotate) once around its axis.

This means that the one side of the Moon, known as the “near side”, is always facing

Earth, and the other “far side” is always facing away from the Earth. The reason that

the rotation and revolution periods of the Moon are different from the time it takes to

complete one cycle of Moon phases is that the Earth is also orbiting around the Sun, and

the Moon thus has to revolve more than 360 degrees around the Earth for the Sun,

Earth and Moon to all align again at the same starting point.

The direction of the Moon’s rotation and revolution is counter-clockwise, when viewed

from above the Moon’s (and Earth’s) North Pole. This is the same direction as the Earth

rotates and revolves.

During a complete 29.5 day cycle of the Moon Phases, the Moon as seen from Earth,

goes from being completely dark, called a “New Moon” to completely lit, called a “Full

Moon”, and then back to a completely dark New Moon again. During the first half of the

cycle, a bit more of the Moon facing Earth is lit each night. These are called the waxing

(brightening) phases of the moon. During the last half of the cycle, a bit less of the

Moon facing Earth is lit each night. These are called the waning (darkening) phases of

the Moon.

Each phase of the Moon has been given a name. When less than a quarter of the Moon

facing earth is lit, it is called a “Crescent Moon”. When about half of the Moon facing

Earth is lit, it is called a “Quarter Moon.” When about three-quarter’s of the Moon facing

Earth is lit, it is called a “Gibbous Moon”. The complete cycle of Moon Phases, with their

full names, are shown in the flow map diagram on the next page. Note that there are

two quarter moons, two crescent moons and two gibbous moons, one each in the

waxing side of the cycle, and one in the waning side of the cycle.

Staar Moon Phases Science Worksheets