semimajor axis
- noun
- /ˌsɛmiˈmeɪdʒər ˈæksɪs/
- Specialized
:
semieje mayor
- The length of the semimajor axis determines how elongated the ellipse is.
Examples
-
To the extent that the parent star's mass is known from its spectrum and luminosity, the periodicity of the Doppler signal yields the planetary orbit's semimajor axis a.
Academic text (2004) -
In astronomy, the semimajor axis is crucial for calculating the distance of planets from their sun.
-
The semimajor axis of an ellipse is measured from its center to the furthest point on the perimeter.
Synonyms
Half of the longest line across an ellipse
How Long
Surface Forms
Morphology
The compound is compositionally regular: 'semimajor' (semi- = half + major = larger diameter) specifies a half of the major dimension and 'axis' denotes the relevant line, so the overall meaning (the axis corresponding to half the longest diameter) is directly inferable from the parts. This is a standard technical naming pattern found across languages, so a learner who knows the constituents should be able to derive the meaning.
Etymology
Semimajor axis comes from a simple picture: imagine an oval like an egg and draw the longest line across it. The word axis is that line, major means 'long', and semi means 'half', so the semimajor axis is the half of the longest line from the center to the edge, which is why it measures how far an object is in an oval orbit.
