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

Estimate the maximum and minimum time it takes a radar signal to make the round trip between Earth and Venus, which has a semimajor axis of 0.72 AU.

From Textbooks • Oct. 13, 2016

Also, recall that a planet’s semimajor axis, a, is equal to its average distance from the Sun.

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

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

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