Halfmoon is a term used to describe the lunar phase when the Moon appears as a semi-circle. This occurs when the Moon is at a 90-degree angle relative to the Earth and the Sun. During this phase, half of the Moon's surface is illuminated, making it easy to recognize in the night sky. The Halfmoon phase is part of the lunar cycle, which lasts about 29.5 days. It is also known as the first quarter or last quarter moon, depending on its position in the cycle. Observing the Halfmoon can help people learn more about the Moon and its phases.