What is the apparent shape of the Moon's directly sunlit portion as viewed from Earth called?

What is the apparent shape of the Moon's directly sunlit portion as viewed from Earth called?

• A. Lunar phases
• B. Moon phases
• C. Illumination
• D. Phase

Answer: (A)

The apparent shape of the Moon’s sunlit portion as seen from Earth is described by the lunar phases. As the Moon orbits Earth, the portion that is lit by the Sun changes, producing a repeating sequence—new moon, crescent, first quarter, gibbous, full, and back to new. This collection of shapes over the cycle is what astronomers call the lunar phases. Saying “phase” would refer to one moment in that cycle, while “lunar phases” names the whole pattern. Illumination, by contrast, refers to brightness, not shape, and “Moon phases” is a common everyday term, but the standard formal term is lunar phases.

The apparent shape of the Moon’s sunlit portion as seen from Earth is described by the lunar phases. As the Moon orbits Earth, the portion that is lit by the Sun changes, producing a repeating sequence—new moon, crescent, first quarter, gibbous, full, and back to new. This collection of shapes over the cycle is what astronomers call the lunar phases. Saying “phase” would refer to one moment in that cycle, while “lunar phases” names the whole pattern. Illumination, by contrast, refers to brightness, not shape, and “Moon phases” is a common everyday term, but the standard formal term is lunar phases.