Astronomy Concepts

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Apparent Retrograde Motion

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The apparent backward movement of a planet as observed from Earth, caused by the relative positions and motions of Earth and the planet.

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Eccentricity

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A measure of how an orbit deviates from being circular. An orbit with an eccentricity of 0 is a perfect circle.

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Exoplanets

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Planets that orbit a star outside the solar system.

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Gravity

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The force by which a planet or other body draws objects toward its center.

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Kepler's Laws

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Three laws that describe the motion of planets around the sun.

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Nebula

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A giant cloud of dust and gas in space, often a region where new stars are born.

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Orbit

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The curved path of a celestial object or spacecraft around a star, planet, or moon.

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Planets

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Celestial bodies orbiting a star, massive enough to be rounded by their own gravity, but not massive enough to cause thermonuclear fusion.

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Satellites

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Objects that orbit around planets, which can be natural, like moons, or artificial.

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Solar System

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The collection of eight planets and their moons in orbit around the sun, together with smaller bodies such as asteroids, meteoroids, and comets.