semimajor axis

American  

[sem-ee-mey-jer, sem-ahy-, sem-ee-, sem-ahy-] / ˈsɛm iˈmeɪ dʒər, ˈsɛm aɪ-, ˌsɛm i-, ˌsɛm aɪ- /

noun

1. Geometry. one half the major axis of an ellipse.

2. Astronomy. one half the major axis of the ellipse that one celestial body describes around another, as a planet around the sun or a satellite around a planet, equivalent to the mean distance between the two bodies.

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Etymology

Origin of semimajor axis

First recorded in 1925–30; semi- + major

Example Sentences

Venus’ orbital period is 0.62 year, and its semimajor axis is 0.72 AU.

From Textbooks • Oct. 13, 2016

Half this distance—that is, the distance from the center of the ellipse to one end—is the semimajor axis, which is usually used to specify the size of the ellipse.

From Textbooks • Oct. 13, 2016

The size and shape of an ellipse are completely specified by its semimajor axis and its eccentricity.

From Textbooks • Oct. 13, 2016

It has a semimajor axis of 84 AU.

From Textbooks • Oct. 13, 2016

This is the equation of a horizontal ellipse centered at the origin, with semimajor axis 4 and semiminor axis 3 as shown in the following graph.

From Textbooks • Mar. 30, 2016