ICSE Class 9 Answered

a. The appearance of the Moon changes as it revolves around the Earth. While sometimes we can see only half Moon, at other time we can see the full Moon. This change in the shape of the Moon which is visible to us from the Earth is known as the phases of the Moon.

b. The following are the phases of the Moon:

New Moon: When the Moon does not appear on the Earth, it is known as the New Moon. It does not appear to us because when the Moon is in between the Earth and the Sun, the part of the Moon facing the Earth is in complete darkness.

Waxing Crescent: When the thin illuminated surface of the Moon appears three days after the New Moon, it is known as the Waxing Crescent.

First Quarter: On the seventh day after the New Moon, the Moon appears in the form of a half circle. This is known as the First Quarter.

Waxing Gibbous: When the three fourth illuminated circle of the Moon appears, it is known as the Waxing Gibbous.

Full Moon: When the full Moon appears in a complete circle, it is known as the Full Moon. The  Full Moon appears when the Moon is far away from the Sun than the Earth.

Waning Gibbous: When the Moon begins to wane, it is known as the Waning Gibbous.

Last Quarter: On the twenty first day after the New Moon, the Moon again appears as the luminous half circle. This phase is called the Last Quarter.

Waning Crescent: On the 25^th day after the New Moon, only a thin illuminated circle of the Moon appears. This is known as the Waning Crescent.