Q:

How does the moon change its shape?

A:

Quick Answer

The changing shapes of the moon, known as phases, are actually just changes in perspective from Earth, which appear as a change in the moon's form. From Earth, only one side of the moon ever appears illuminated by the sun, resulting its apparent change in size.

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Full Answer

The sun provides a directional light source that strikes the moon on its visible side. As the moon orbits Earth, different amounts of the illuminated face of the moon are visible from Earth's surface. This is what is perceived on Earth as a change in the moon's shape. It should also be noted that at times the Earth passes between the moon and the sun, blocking some of the light source and casting a shadow over the face of the moon. This is known as a lunar eclipse.

There does exist an almost imperceptible change in the physical shape of the moon as a result of the Earth's gravitational pull, with the reverse being true as well. This cannot be visibly detected, but it is the reality of the gravitational forces being exerted by both bodies. The same gravitational pull also causes tidal changes in the Earth's oceans and minor fluctuations in the motion of tectonic plates.

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Related Questions

  • Q:

    What is the purpose of the moon?

    A:

    The gravitational pull of the moon controls the rise and fall of tides on Earth and slows the planet's rotation, while the phases of the moon serve as calendar markers for human beings. High tides occur on the portion of the Earth closest to the moon and the portion farthest away. Low tides occur between those two points.

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  • Q:

    Why do moon phases occur?

    A:

    The different moon phases occur from its revolutions around the Earth. The moon goes through distinct phases with one complete rotation around the world, including a new phase, first quarter phase, third quarter phase and full moon. Variations in light and shape of the moon change within these phases too, as the moon goes through a waxing gibbous stage en route to the full moon stage, then transforms into a waning gibbous before reaching the third quarter phase.

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  • Q:

    Why does the moon wax and wane?

    A:

    The moon appears to wax and wane through different phases due to how much of its illuminated surface is visible from Earth. At any given time, half the moon is illuminated by the sun's light. Depending on where the moon is in relation to the Earth, the amount of illuminated surface changes. The ratio of illuminated surface to shadowed surface creates the phases.

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  • Q:

    Why does the moon go through phases?

    A:

    The phases of the moon are caused by the relative positions of the sun, Earth and moon. The moon travels around the Earth, taking just over 29 days to complete a single orbit. The sun illuminates the moon from various angles as it changes position relative to the Earth.

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