The amount of the moon visible at any given time depends on its phase.

Here's a breakdown:

* New Moon: 0% visible (completely dark)

* Waxing Crescent: Less than 50% visible (a thin sliver)

* First Quarter: 50% visible (half illuminated)

* Waxing Gibbous: More than 50% visible (growing towards full)

* Full Moon: 100% visible (entire face illuminated)

* Waning Gibbous: More than 50% visible (shrinking from full)

* Last Quarter: 50% visible (half illuminated)

* Waning Crescent: Less than 50% visible (a thin sliver)

So, while the entire moon is always there, only a portion of it is illuminated by the sun and therefore visible from Earth at any given time.