Facts that Matter

•Celestial Objects:Objects, such as the stars, the planets, the moon and many other objects, in the sky are called celestial objects.

•Phases of the Moon:The various shapes of the bright part of the moon as seen during a month are called phases of moon.

The moon revolves round the earth. It also revolves round the sun along with the earth. The various stages of the moon during a month are shown in Fig. 17.1.

In position 1, the part of the moon facing earth does not receive light from the sun.

Hence it appears dark. The other part of the moon that is facing away from earth is lit by the sun light. This position of moon, when it appears dark on earth is known as new moon.

In position 2, 3 and 4, we see the moon not as a full disc but as a cresent. Position 2 of the moon is known as cresent moon, Position 3 as first quarter and position 4 as Gibbous (bright part is greater than a semicircle) moon.

In position 5, the Sun's rays fall directly on the part of the moon facing earth. In this position we see the moon as a full disc of light. This position of moon is known as full moon.