Every night you can the the Moon, our good old satellite.
But that is not really true.
You can not see the Moon every night.
When there is new moon, you can not see him. Why is that?
The Moon revolves the Earth.
Both, Earth and Moon are illuminated by the sun.
So we can only see the Moon, when we can see the reflected sunlight.
When is that happened?
When is that not happened?
It happens at any point of the revolution except one point.
This point is when the Moon are exact in the line between Sun and Earth.
Then the Sun illuminates the side of the Moon, who is not in Earth direction.
So someone who stands on the Earth can not see the reflected sunlight - it is new moon.
At any other time of the revolution at least some reflected sunlight will be seen by a person on the Earth.
When the Moon is on the Sun-Earth line, but behind the Earth it is full moon and we can see the whole Moon hemisphere.
May 2015
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