The Moon

Front

Satellite Noun

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[sat-uh-lite]

Back

Satellite

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A celestial body that orbits a planet or smaller body; the Moon is Earth's only natural one.

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Example: The Moon is a natural satellite because it orbits the Earth. Earth's gravity constantly pulls the Moon, while the Moon's forward velocity keeps it moving in a circular path.

Front

Gravity Noun

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[grav-i-tee]

Back

Gravity

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The universal attractive force that exists between any two objects that have mass, holding the solar system together.

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Example: This diagram shows that gravity is a mutual force of attraction, pulling the Moon and Earth toward each other.

Front

Rotation Noun

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[roh-tey-shuhn]

Back

Rotation

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The movement or spinning of a celestial object, such as a planet or moon, on its own internal axis.

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Example: This diagram shows a celestial body, like the Moon, spinning on an imaginary line called an axis. The arrows indicate the direction of this spinning motion.

Front

Revolution Noun

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[rev-uh-loo-shuhn]

Back

Revolution

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The movement of one celestial object in an orbit around another, such as the Moon's path around Earth.

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Example: This diagram shows the Moon's revolution, which is its orbital path around the Earth, indicated by the yellow arrows.

Front

Orbit Noun

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[or-bit]

Back

Orbit

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The curved path a celestial object or spacecraft follows as it revolves around another object due to gravity.

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Example: This diagram shows the Moon following a curved path, its orbit, around the Earth, held in place by the pull of gravity.

Front

Synchronous Rotation Noun

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[sing-kruh-nuhs roh-tey-shuhn]

Back

Synchronous Rotation

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An orbital state where an object's rotation period matches its orbital period, keeping one side facing its primary.

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Example: This diagram shows the Moon rotating exactly once as it orbits the Earth, which is why we always see the same face of the Moon.

Front

Moon Phases Noun

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[moon fay-ziz]

Back

Moon Phases

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The different appearances of the Moon from Earth, caused by the changing angles of its sunlit portion.

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Example: This diagram shows how the Moon's orbit around Earth causes different amounts of its sunlit side to be visible, creating the moon phases.

Front

Waxing Adjective

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[wak-sing]

Back

Waxing

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The period in the lunar cycle when the visible illuminated portion of the Moon is gradually increasing in size.

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Example: This diagram shows that 'waxing' means the visible, sunlit part of the Moon is growing, progressing from a New Moon to a Full Moon.

Front

Waning Adjective

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[wey-ning]

Back

Waning

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The period in the lunar cycle when the visible illuminated portion of the Moon is gradually decreasing in size.

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Example: This diagram shows the full lunar cycle, where 'waning' is the period after the full moon when the visible illuminated portion gradually gets smaller.

Front

Exosphere Noun

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[ek-soh-sfeer]

Back

Exosphere

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The outermost region of a satellite's atmosphere, characterized by extremely low density and escaping gas particles.

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Example: The image shows the layers of Earth's atmosphere, with the exosphere as the outermost layer where satellites orbit, before the vacuum of space.