Phases of the Moon

By Jordan Estridge Per. 2

What Are Moon Phases?

Lunar phases, or Moon phases, are the shapes of the illuminated part of the moon as seen from Earth. The phases change in a constant cycle over approximately one month as the Moon orbits around Earth. The position of the Moon and Sun relative to Earth also play an important role. Some examples of a few Moon Phases as seen from Earth are shown to the right. One thing to remember is that the Moon does not create its own light when illuminated in the night sky, it is simply the reflection of the Sun's rays off the Moon's surface resulting in its light.

As Seen From...

You will notice that a lot of the time pictures, people, captions, me, etc. that show or talk about Moon Phases will say 'as seen from Earth' or 'as seen from Space.' What does this mean? This means that the picture or diagram of the Earth's Moon Phases are either seen from a person standing on Earth's surface or seen from an astronaut hanging on to an asteroid and flying by Earth or in Space on the International Space Station and looking down on the Moon, Earth, and Sun as the Moon Phases take place.

'As Seen From' Examples

"Moon Phases"

Moon Phases

As the Moon orbits Earth, the Sun casts a shadow on the part of the Moon that is facing away from the Sun and lights up the part that is facing it. Add in the slow revolving rate of the Earth, and this is what creates the Moon Phases. Looking at the picture below, which is seen from Space, the Moon Phases all have a dotted line going through the middle of the phase. The part facing Earth is what we would see (the white dot is our fixed point on Earth). Notice, if you look just at the half of the part of the moon facing Earth, it changes accordingly to the phases as it moves in a counter clockwise direction.
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Waning v.s Waxing

The Waxing phases (the first of the Moon Phase cycle starting from the New Moon to the Full Moon) are getting bigger since it's starting at the New Moon (0%) and going to the Full Moon (100%). Since the New Moon is the smallest percent, the only way to get bigger are the phases that we call Waxing phases that include (in order) the Waxing Crescent, the 1st quarter, and the Waxing Gibbous.


The Waning phases (the second part of the Moon Phase cycle starting from the Full Moon to the New Moon) are getting smaller since you're starting at the Full Moon (100%) and going to the New Moon (0%). Since the Full Moon is the biggest percent, the only way to get smaller are the phases that we call Waning phases that include (in order) the Waning Gibbous, the 3rd (aka Last Quarter), and the Waning Gibbous.

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1st Quarter v.s 3rd Quarter

1st Quarter v.s 3rd Quarter

Similarities:

The 1st Quarter and 3rd Quarter (also known as the Last Quarter) are similar in that they both have 50% light showing, or half of the moon is showing. They also are on the same "side" of the moon. Because of the rate of revolution of the Moon and Earth, a person on Earth will never see the backside of the Moon, therefore the 1st and 3rd Quarter phases are on the same side as the moon (all phases in general).


Differences:

The 1st Quarter Moon Phase has light on the right while the 3rd Quarter Moon Phase has light on the left. They're also in different positions in relationship to the Earth and Sun (on different sides) when the phase occurs. Looking at the photo above (underneath the 1st and 3rd Quarter title), you can see this a little clearer.