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

Earth’s orbital period is 1.00 year, and its semimajor axis is 1.00 AU.

From Textbooks • Oct. 13, 2016

Kepler’s third law: The square of a planet’s orbital period is directly proportional to the cube of the semimajor axis of its orbit.

From Textbooks • Oct. 13, 2016

If the major axis of an ellipse is 16 cm, what is the semimajor axis?

From Textbooks • Oct. 13, 2016

Thus, Mars’ semimajor axis in astronomical units must be 1.52 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