Gravity and the Solar System

Front

Orbit Noun

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[or-bit]

Back

Orbit

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The curved path that an object follows as it travels around another object in space due to gravitational attraction.

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Example: The Moon's forward velocity and Earth's gravitational pull balance each other, causing the Moon to follow a curved path, or orbit, around Earth.

Front

Ellipse Noun

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[ih-lips]

Back

Ellipse

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A regular oval shape, not a circle, that describes a planet's path of orbit and has two focal points.

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Example: This diagram shows that a planet's path, or orbit, around the Sun is not a perfect circle but an oval shape called an ellipse.

Front

Focus Noun

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[foh-kus]

Back

Focus

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One of two fixed points within an ellipse; the Sun is located at one focus of a planet's elliptical orbit.

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Example: This diagram shows a planet's elliptical orbit, where the Sun is located at one of the two key points called foci (the plural of focus).

Front

Perihelion Noun

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[per-i-hee-lee-uhn]

Back

Perihelion

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The point in a planet's elliptical orbit where it is nearest to the sun, resulting in its fastest orbital speed.

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Example: This diagram shows Earth's elliptical orbit, labeling 'Perihelion' as the point where Earth is closest to the Sun, which occurs in January.

Front

Aphelion Noun

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[a-fee-lee-uhn]

Back

Aphelion

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The point in a planet's elliptical orbit where it is farthest from the sun, resulting in its slowest orbital speed.

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Example: This diagram shows Earth's elliptical orbit, highlighting 'Aphelion' as the point where Earth is farthest from the Sun, contrasted with 'Perihelion', the closest point.

Front

Orbital Period Noun

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[or-bi-tuhl peer-ee-uhd]

Back

Orbital Period

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The time it takes for a celestial body to complete one full orbit around another object, such as the sun.

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Example: This diagram shows that objects at different distances from Earth, like the Moon and a satellite, take different amounts of time (T) to complete one full orbit.

Front

Gravity Noun

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[grav-i-tee]

Back

Gravity

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The fundamental force of attraction between any two objects with mass, which is responsible for keeping planets in their orbits.

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Example: This image shows that gravity is a force that pulls objects towards the center of a massive body, like the planet Earth.

Front

Mass Noun

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[mas]

Back

Mass

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The amount of matter in an object, which directly affects the strength of the gravitational force it exerts or experiences.

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Example: This diagram shows that two objects with mass, like the Earth and another celestial body, exert an equal and opposite gravitational force (F) on each other.