Astronomy

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Geocentric Adjective

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[jee-oh-sen-trik]

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Geocentric

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A model of the universe in which a stationary Earth is at the center of all celestial bodies.

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Example: This diagram shows the geocentric model, an early theory where the Earth is at the center of the universe, and the Sun, Moon, and planets orbit it.

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Heliocentric Adjective

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[hee-lee-oh-sen-trik]

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Heliocentric

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A model of the universe in which the Sun is at the center and planets revolve around it.

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Example: This diagram shows the heliocentric model, where the Earth follows an orbital path around the Sun, which is at the center.

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Rotation Noun

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[roh-tey-shuhn]

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Rotation

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The spinning motion of a planet or other celestial body on its own axis, which causes day and night.

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Example: This diagram shows the Earth spinning on its tilted axis, which is called rotation. Sunlight illuminates one side, creating day, while the other side is in shadow, creating night.

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Revolution Noun

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[rev-uh-loo-shuhn]

Back

Revolution

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The orbital motion of one celestial body around another, which determines the length of a year for a planet.

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Example: The Moon revolves around the Earth in a path called an orbit, held in place by the balance between its forward velocity and Earth's gravity.

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Quantitative Data Noun

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[kwon-ti-tey-tiv dey-tuh]

Back

Quantitative Data

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Information that can be measured and written down with numbers, such as astronomical observations of planetary positions.

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Example: This diagram shows a barometer measuring atmospheric pressure, resulting in a specific number (760 mm), an example of quantitative data used in astronomy.

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Orbit Noun

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[awr-bit]

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Orbit

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The curved, repeating path that a celestial object takes around another object due to gravitational attraction.

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Example: An orbit is the curved path an object in space takes around another due to gravity, like the Moon's path around the Earth.

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Ellipse Noun

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[ih-lips]

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Ellipse

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A regular oval shape, which Johannes Kepler discovered is the true shape of a planet's orbit around the sun.

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Example: This diagram shows Earth's orbit around the Sun is not a perfect circle but an oval shape called an ellipse, causing its distance to vary.

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Phases Noun

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[feyz-iz]

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Phases

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The different ways a celestial body appears from Earth as it orbits another body, revealing varying amounts of illumination.

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Example: This diagram shows the Moon orbiting the Earth. As the Moon moves, the sun lights up different parts of it, causing the changing shapes, or phases, we see.

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Inertia Noun

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[in-ur-shuh]

Back

Inertia

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The property of matter by which it continues in its existing state of rest or uniform motion in a straight line.

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Example: This image shows an unbalanced force causing a car to accelerate, which demonstrates how to overcome inertia, not the concept of inertia itself.

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Gravity Noun

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[grav-i-tee]

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Gravity

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A natural force of attraction between any two objects with mass, which keeps planets in their orbits.

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Example: This image shows that Earth's gravity is a force that pulls everything from all directions towards the planet's center.