Page 147 - Innovator's Science-8

THE MOON'S CYCLE OF PHASES

The Moon completes one full orbit around Earth in about 29.5 days. As it
moves, we see it change from a full circle to a thin crescent and then
disappear completely, only to grow again. The day on which the entire
bright surface of the Moon is visible is called the Full Moon Day , and the day
Science it is not visible at all is called the New Moon Day .
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From the New Moon to the Full Moon, the bright portion of the Moon
Testimony
‘Waxing’ means the gradually increases - this period is called the waxing phase .
visible por on of the From the Full Moon back to the New Moon, the bright part decreases - this
moon is growing, while
‘waning’ means it is period is called the waning phase .
shrinking. The en re cycle We noticed that the Moon's position at sunrise or sunset changes a little bit
of phases takes about
29.5 days. each day. This happens because the Moon is moving forward in its path
around the Earth while the Earth is spinning on its axis every 24 hours. Since
the Moon moves along in its orbit, the Earth has to spin a little more than
one full turn for the Moon to appear in almost the same place in the sky as
the day before. This is why the Moon seems to shift position at the same

time each day.

(b) In the same time of
one day, the Moon would Moon's orbit around
revolve a bit further in its the Earth
orbit around the Earth

(c) So I will find the (a) Today the Moon is
Moon overhead about overhead. The Earth
50 minutes later than will rotate once in one
Science has rotated some more day, and I will be back
today, when the Earth
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at this same position.
Testimony
The Moon's orbit around
Earth is tled by about 5
degrees compared to
Earth's orbit around the
The Moon takes about 50 minutes longer το come
Sun. Because of this slight
back to nearly the same position in the sky
lt, the three bodies—
Sun, Earth, Moon – rarely WHY THE MOON'S PHASES ARE NOT CAUSED BY SHADOWS
align perfectly; that's why
we don't see an eclipse A common misunderstanding is that the Moon's changing shape, or its
every month even though phases, happens because of Earth's shadow falling on it.
the Moon passes
between Earth and the In reality, the phases are caused by how sunlight falls on the Moon and how
Sun regularly. the Moon, Earth, and Sun move with respect to one another. Only when

Earth's shadow actually covers the Moon do we get a lunar eclipse , which is

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Science-8