The revolution of the Moon around the Earth makes the Moon appear as if it is changing shape in the sky. From Earth we see the Moon grow from a thin crescent to a full disk (or full moon) and then shrink back to a thin crescent again before vanishing for a few days.
The Moon phases are produced by the alignment of the Moon and the Sun in the sky.
The lit part of the Moon always points the way to the Sun.
The changing shape of the bright part of the Moon that we see is called its phase.
The moon is illuminated because it reflects the light from the sun. The part of the moon facing the sun is lit up. The part facing away from the sun is in darkness.
The phases of the Moon depend on its position in relation to the Sun and Earth. As the Moon makes its way around the Earth, we see the bright parts of the Moon's surface at different angles. These are called "phases" of the Moon.
The phases of the moon work in a cycle starting with the new moon.
There are eight phases of the moon
The phases are named after how
much of the moon we can see, and whether the amount visible is
increasing, or decreasing each day.
![Phases of the moon as seen in the Northern Hemisphere](http://www.woodlands-junior.kent.sch.uk/time/moon/phases.gif)
Phases of the moon as seen in the Northern Hemisphere
![](http://www.woodlands-junior.kent.sch.uk/time/moon/phasessouth.gif)
Phases of the moon as seen in the Southern Hemisphere
It takes our Moon about 29.5 days to completely cycle through all eight phases. This is known as a Lunar month
The Moon orbits near the equator of the Earth. In the northern
hemisphere, we're standing on the opposite side of the globe from
countries in the southern hemisphere i.e. we are "upside down" from each
other! We therefore see the Moon from a completely different vantage
point from each other.
The first and last quarter moons mark the halfway points between the new
moon and full moon. The first quarter moon is illuminated on the right
hand side. The last quarter moon is illuminated on the left hand side.
It seems conflicting to call a half full moon first of last quarter, but
the quarter refers to the position of the moon in the sky, not it's
phase. A quarter moon is one quarter of a full circle (90 degrees) away
from the sun.
WORKSHEET
The diagram below shows the Earth and Moon as viewed from space far above the north pole of the Earth.Write the name of the phrases.
One of the biggest misconceptions about the Moon is that its phases are
caused by the Earth's shadow. The Earth's shadow causes eclipses, but it
has nothing to do with phases. Rather, the phases of the Moon are
produced by the alignment of the Moon and the Sun in the sky.
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The orientation of Sun and Moon determines the phase of the Moon. At new
moon, the angular distance of the sun and moon is small, less than a
few degrees. At first quarter, when the moon is half full, the Moon lies
90 degrees east of the Sun. As an example, if you were to point to the
setting sun with one arm and to the moon with the other, the angle
between your arms would be 90 degrees. At full, the moon is 180 degrees
from the sun and at last quarter, it is 90 degrees west of the sun.
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The new moon is essentially invisible because it is between the earth
and sun and therefore lost in the glare of the sun. Even on day 2 or 3
it is tough to spot the moon because it is just the tiniest sliver and
still very close to the sun. The waxing crescent moon grows till it is
about half full in the phase we call first quarter. From there it grows
to full moon and then begins to shrink back to third quarter, waning
crescent and finally back to new moon.
![](http://starryskies.com/The_sky/events/lunar-2003/phases.gif)
![](http://starryskies.com/The_sky/events/lunar-2003/waxing.sunset.position.png)
The lighted part of the Moon always points the way to the Sun. This
means that a waxing crescent moon in the western sky at sunset has the
lighted part on the right which is the direction of the Sun. The
sequence of the lunar phases always proceeds with the lighted part of
the Moon growing from right to left until the moon reaches full. After
full moon, the light recedes from right to left until new moon.
The line boundary between dark and light on the Moon is called the
terminator. It is rarely an even line because the surface of the Moon is
not smooth. The terminator is closest to a straight line at first and
last quarter. Librations affect exactly what portion of the face of the
Moon is facing the Earth, during first and last quarter phase, the
terminator's exact location may vary. This is illustrated when the
terminator does not line up with the Moon's meridian at first and last
quarter. In other words, you'd think that during first and last quarter
when the Moon is half full, that the meridian (the imaginary line which
runs from north to south on the Moon,) would be right on the terminator,
but it isn't so. In fact the terminator can be almost 8 degrees off to
either side of the meridian.
WORKSHEET
The diagram below shows the Earth and Moon as viewed from space far above the north pole of the Earth.Write the name of the phrases.
Read the definitions, then label the moon phases diagram below. |
Definitions |
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Crescent Moon - when we can see only a sliver of the moon's disk (the side of the moon facing us)
Full Moon - when the moon's disk is light because the Earth is between the sun and the moon
Gibbous Moon - when we can see roughly three-quarters of the moon's disk Half Moon - (also called quarter moon) when we can see one half of the moon's disk (this is one-quarter of the entire moon's surface) |
New Moon - when the moon's disk is dark (and invisible to us) because the moon is between the sun and the Earth
Quarter Moon - (also called half moon) when we can see one half of the moon's disk (this is one-quarter of the entire moon's surface)
Waning Moon - when the moon seems to be getting smaller, going from full to gibbous to half to crescent to new Waxing Moon - when the moon seems to be getting bigger, going from new to crescent to half to gibbous to full |
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