Q:

How does the moon change its shape?

A:

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.

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 causes moon phases?

    A:

    Moon phases are caused by the motions of the Earth and moon as they relate to the sun. Phases occur as the Earth-facing side of the moon changes over the course of 29.5 days when the moon revolves around the planet. When the angle of sunlight reflecting off the moon changes, humans observe different lighting levels from the moon.

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  • Q:

    What causes the phases of the moon?

    A:

    The phases of the moon are caused by the light from the sun and the position of the moon with regard to the Earth and sun. Depending on these positions, the moon appears to be in any one of eight major phases from Earth. These phases are full, waning gibbous, third quarter, waning crescent, new, waxing crescent, first quarter and waxing gibbous. Each phase lasts approximately seven days.

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  • Q:

    Why are we able to see different phases of the moon?

    A:

    The moon orbits around the Earth on a 29 day cycle. Half of the moon is always lit by the sun's rays but different amounts of this illumination can be seen from Earth depending on the angle the moon makes with the sun relative to the Earth.

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  • Q:

    Why does the moon change shape during the month?

    A:

    The moon does not physically change its shape. As it orbits the Earth, it goes through phases, and sunlight and shadows create a slightly different look each night. It takes about one month for the moon to completely cycle through its phases.

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