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Moon Phases

The moon is at her full, and riding high,
   Floods the calm fields with light.
     The airs that hover in the summer sky
       Are all asleep to-night.

William Cullen Bryant

Vocabulary to know:

Revolution - the motion of the moon around the Earth, one complete orbit.

Phase - the shape of the moon as seen from Earth

Waxing - describes a moon that seems to be getting bigger each night

Waning - describes a moon that seems to be getting smaller each nigh

Crescent - a moon that is smaller that a quarter moon, but larger that the new moon

Gibbous - a moon that is larger than a quarter moon, but smaller than a full moon

The revolution of the Moon around the Earth makes the Moon appear as if it is changing shape in the sky.

• This is caused by the different angles from which we see the bright part of the Moon's surface.
• These are called "phases" of the Moon.

The phase you see when you look at the moon depends on its location in relationship to the sun and Earth.

The Moon doesn't create any light itself; it just reflects the light of the Sun.

The Moon passes through eight major phases during a cycle that repeats itself every 29.5 days. Cycles are a continuous process; there is no beginning or end.

• The phases always follow one another in the same order

.

New Moon

• The moon is lined up between the Earth and Sun
• When the Moon is exactly lined up with the Sun (as viewed from Earth), we experience an eclipse
• The illuminated half of the moon is facing away from the Earth, and therefore the part that faces us is all dark

The Moon and the Sun rise and set at about the same time


Waxing Crescent Moon

• As the Moon moves around the Earth, we see more and more of the illuminated half
• It looks as if the moon is getting bigger each night
• The moon is smaller than a quarter moon
• The Moon is waxing.

Quarter Moon

• A week after the new moon, when the Moon has completed about a quarter of its turn around the Earth, we can see half of the illuminated part
• From Earth, we are now looking at the sunlit side of the Moon from off to the side.
  • A quarter of the Moon
• The first quarter phase.
• The Moon is now one-quarter of the way through the lunar month

Waxing Gibbous Moon

• During the next week, we keep seeing more and more of the illuminated part of the Moon
• Waxing gibbous
  • Gibbous means "humped"
  
  

Full Moon

• Two weeks after the new moon, the moon is now halfway through its revolution around the Earth
• The illuminated half is facing the Earth
• We can see a full disk
  • Full moon
• At this time the Moon rises at the time the Sun sets, and it sets when the Sun rises
• If the Moon happens to align exactly with the Earth and Sun, then we get a lunar eclipse. the full sunlit face of the Moon.
• The Moon has now completed one half of the lunar month
  

Waning Gibbous Moon

• From this point, until it becomes new again, the illuminated part of the Moon that we can see gets smaller
• A gibbous moon is larger than a quarter moon, but smaller than the full moon
  • Waning
• The first week after the full moon, the phase is called waning gibbous

• Three weeks after the new moon , we again can see half of the illuminated part
• This is usually called last quarter
  • Sometimes called third quarter
• The side that we saw dark at the first quarter phase is now the lit side

• During the fourth week, the Moon appears to get smaller and smaller
• Waning crescent .
  
  

Original Graphics Sources

http://home.hiwaay.net/~krcool/Astro/moon/moonphase/

http://www.astro.umd.edu/education/astro/moon/phases.html