Which term describes a moon phase that appears as a complete circle from Earth?

Which term describes a moon phase that appears as a complete circle from Earth?

• A. Full Moon
• B. Gibbous Moon
• C. Quarter Moon
• D. New Moon

Answer: (A)

Understanding how the Moon’s lit portion faces Earth is the key idea. When the Sun-lit side of the Moon is completely facing us, we see the entire disk illuminated, which is a Full Moon. This occurs when the Moon is opposite the Sun in the sky, so Earth sits between Sun and Moon. The other phases describe different amounts of illumination: a Gibbous Moon is more than half lit but not fully illuminated; a Quarter Moon shows half of the Moon’s near side lit; a New Moon has the near side dark, with the lit side away from Earth, making it generally invisible at night. So, the term for a Moon phase that looks like a complete circle from Earth is the Full Moon.

Understanding how the Moon’s lit portion faces Earth is the key idea. When the Sun-lit side of the Moon is completely facing us, we see the entire disk illuminated, which is a Full Moon. This occurs when the Moon is opposite the Sun in the sky, so Earth sits between Sun and Moon.

The other phases describe different amounts of illumination: a Gibbous Moon is more than half lit but not fully illuminated; a Quarter Moon shows half of the Moon’s near side lit; a New Moon has the near side dark, with the lit side away from Earth, making it generally invisible at night. So, the term for a Moon phase that looks like a complete circle from Earth is the Full Moon.