What is defined as the longest radius of an ellipse, representing half its longest diameter?
Answer
The semi-major axis ($a$)
The semi-major axis, symbolized as $a$, serves as the fundamental dimension describing the size of the elliptical orbit. Specifically, it is defined as half the longest diameter of the ellipse. Beyond its geometric definition, the semi-major axis holds significant physical meaning in orbital mechanics: it represents the planet's average distance from the Sun over the entirety of its full revolution around the star. This parameter is crucial for calculating orbital periods and energy levels within the solar system.
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