Actually a little bit more than half of the Moon's surface is observable from Earth.
If the Moon rotates, all its sides should be seen on a regular basis, as well as different sides of the Moon should be seen from different parts of the Earth and throughout the different seasons and hours of the day. I'm sure you know the common explanation that the Moon rotates the same speed as it orbits the Earth but such a coincidence is about 1:10.000.000 to happen assuming that there are millions of planets and satellites in our Universe, and they each have their own unique speed. Very, very strange indeed.
The side of the Moon that faces Earth is called the near side, and the opposite side the far side. The far side is often inaccurately called the "dark side", but in fact, it is illuminated exactly as often as the near side: once per lunar day, during the new moon phase we observe on Earth when the near side is dark.
NOTE: This gadget calculates the moon phase based on YOUR computer system date and time zone.
Choose your hemisphere clicking the symbol at right of the clock hour.
Thanks to NASA Brain Bites: So You Always Wanted to Ask NASA... videos.
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