Phases of the Moon

• Moon

  • Brightest and largest object in our night sky
  • Makes Earth a more livable planet by moderating the wobble on its axis that leads to a relatively stable climate
  • Causes tides that create a rhythm that has guided humans for thousands of years
  • Likely formed after a Mars-sized body collided with Earth several billion years ago
  • Earth's only natural satellite
• Distance and size

  • On average 238,855 miles (384,400 km) away from Earth
  • Diameter is about 2,159 miles (3,474 km), roughly one-quarter of the size of Earth
• Moon's surface


  • Covered in craters, mountains, valleys, and lava plains formed by impacts from asteroids and comets, volcanic eruptions, and lunar quakes
  • Has no atmosphere (surface is constantly bombarded by radiation from the Sun and cosmic rays), giving moon a dark and dusty appearance though the lunar soil is light-colored
• Moon's rotation and revolution

  1. Tidally locked to Earth (always shows the same face to us) because the gravitational pull of Earth has slowed the moon's rotation so that it matches its revolution period

  2. Takes 27.3 days to complete one orbit around Earth
• Moon exploration


  • First celestial body visited by humans
  • Apollo 11 mission in 1969 landed the first astronauts, Neil Armstrong and Buzz Aldrin, on the lunar surface
• Moon has phases that takes about 29.5 days to go through the whole cycle
• Phases of the Moon

  • New Moon
  • Waxing Crescent
  • First (Waxing) Quarter
  • Waxing Gibbous
  • Full Moon
  • Waning Gibbous
  • Last/Third (Waning) Quarter
  • Waning Crescent
• New Moon


  • The moon is between Earth and the Sun, thus, none of the lunar half we see is illuminated (the side facing us is not lit up)
  • The moon becomes nearly invisible in the night sky
  • Can only be seen during a solar eclipse
• Waxing Crescent


  • The moon's illuminated surface increases (the bright side gets bigger each night)
  • Forms a thin crescent (on the right in the Northern Hemisphere)
• First (Waxing) Quarter


  • Half of the moon is illuminated (like a perfect half circle)
  • The percentage of the lit surface is still increasing
• Waxing Gibbous


  • The moon is more than half full and still increasing its illuminated surface
  • "Gibbous" comes from the Latin for "hump" used to describe a rounded or convex shape
  • "Waxing" means it is getting bigger
• Full Moon


  • The moon is behind Earth with respect to the sun and its face is fully illuminated
  • When we can sometimes see lunar eclipses
• Waning Gibbous


  • The moon is more than half lit but the illuminated surface we can see is decreasing
  • "Waning" means it is getting smaller
• Last/Third (Waning) Quarter

  The moon is half illuminated but the lit area is on the decline
• Waning Crescent


  • The moon shrinks back to a crescent that is less than half full
  • In the Northern Hemisphere, the waning crescent is seen as a thin crescent of light on the left