Earth, Moon, Sun System

As the moon revolves around the Earth, its apparent shape changes in a cyclic mannerAs the moon revolves around the Earth, its apparent shape changes in a cyclic manner The moon’s period of revolution is 27.3 days (The moon revolves approximately 13° per day in its orbit)The moon’s period of revolution is 27.3 days (The moon revolves approximately 13° per day in its orbit) The moon also takes 27.3 days to complete one rotation on its axisThe moon also takes 27.3 days to complete one rotation on its axis Therefore one lunar day is equal to one lunar yearTherefore one lunar day is equal to one lunar year

On earth we can only see the portion of the moon that is illuminated by the sun. The different shapes that we observe are called the PHASES OF THE MOONOn earth we can only see the portion of the moon that is illuminated by the sun. The different shapes that we observe are called the PHASES OF THE MOON

Phases of the Moon New Moon: When the moon lies between the earth and the sun, the dark side of the moon faces the earthNew Moon: When the moon lies between the earth and the sun, the dark side of the moon faces the earth Full Moon: When the moon is on the opposite side of earth from the sun, the whole lighted side is facing earthFull Moon: When the moon is on the opposite side of earth from the sun, the whole lighted side is facing earth It takes 29.5 days for the moon to complete its phasesIt takes 29.5 days for the moon to complete its phases

Phases Video Animation 1 Animation 2

Why does it take longer to complete its phases than to make one revolution?

This occurs because as the moon is orbiting the earth, the earth is moving 1° per day around the sun in its own orbit. So the moon must move another 27.3° to return to the same phase.This occurs because as the moon is orbiting the earth, the earth is moving 1° per day around the sun in its own orbit. So the moon must move another 27.3° to return to the same phase.