Simplified, mechanical-style animation of the Moon orbiting the Earth showing the phases of the moon.

THE MOON changes appearance through the lunar month as it revolves around the Earth. This animation shows in a very simplified way how the sunlight (coming from lower right) illuminates the Earth (bluish-white) and the Moon (grey). The viewpoint is fixed on the Earth and shows the moon rotating around the Earth. This rotation takes just over 27 days (a lunar month) but it takes nearly 30 days for the moon to go through all of its phases as viewed from Earth. The inset at upper right shows the moon as seen from Earth. The phases are full moon, waning gibbous, half moon, waning crescent, new moon, waxing crescent, half moon, and waxing gibbous. Moonlight is simply sunlight reflected from the surface of the moon.

NOTES: The scales are approximately correct for the relative sizes of the Earth and moon but the distance between the two has been greatly reduced. The plane of the moon orbit is, in reality, slightly tilted with respect to the plane of the Earth's orbit around the sun. The Earth and moon are locked in an orbit around each other and actually rotate about the pair's centre of gravity which is towards the surface of the Earth on the side facing the moon. This point is called the barycentre (Greek heavy centre). The moon continues to face the Earth as it orbits around, locked into synchrony by tidal (gravitational) forces. This is equivalent to the moon performing one revolution around its own axis for every complete revolution it makes around the Earth. The gravitational pull of the moon on the Earth distorts the oceans creating the tides.

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