Phases of the Moon

• We always see the same face of the Moon because the Moon day is the same length as the Moon year.

• This is because the Moon's rotational period is the same as it's orbital period.

• The phases of the Moon, or the different shapes of the Moon, are caused by the different angles from which we see the illuminated part of it's surface.

• Half of the Moon is always illuminated, we just cannot always see all of the illuminated part of the Moon.
  
  

• When the Earth, Sun, and Moon are nearly in a straight line, with the Earth in the middle, we have a Full Moon.

• When the Earth, Sun, and Moon are nearly in a straight line, with the Moon in the middle, we have a New Moon.

• Just after and before a New Moon, the dark portion of the Moon is slightly illuminated by earthshine.

• Earthshine is caused by sunlight reflected from the Earth to the Moon and back to the Earth.
  
  
  The Lunar Month