What type of moon is semi-circular and can be seen from Earth?

The semi-circular moon that can be seen from Earth is commonly referred to as a "half moon" or a "first quarter moon." This phase occurs when the moon is one-quarter of the way through its orbit around the Earth, resulting in half of the moon being illuminated and visible from our perspective.

During this phase, the left or right side of the moon appears lit, depending on the time of year and the observer's location. This visibility and the shape is why it is commonly described as semi-circular. It is distinct from the other lunar phases, which include the crescent moon, where only a sliver of the moon is illuminated; the full moon, where the entire face is lit; and the new moon, when the moon is not visible at all because it is positioned between the Earth and the sun.

Understanding the terminology and visual characteristics of the moon phases is crucial in astronomy education and helps clarify why the half moon is specifically described in this manner.