semimajor axis
Definition
- Noun:
- A specific geometric measurement in an ellipse: The
semimajor axisis exactly one-half of the ellipse's longest diameter (the major axis). It is the distance from the exact center of the ellipse to the farthest point on its perimeter along that longest line.
Usage
The term semimajor axis is used almost exclusively in technical contexts, primarily geometry and astronomy.
* In geometry, it is a fundamental parameter for describing the size and shape of an ellipse.
* In astronomy, it is a crucial orbital element, representing the average distance from an orbiting body (like a planet) to the body it orbits (like a star) at the focus of the elliptical orbit.
Examples
- Noun:
- In the diagram, the length of the
semimajor axisis labeled 'a'. - Astronomers calculated the planet's
semimajor axisto determine its orbital period. - The
semimajor axisof Earth's orbit around the Sun is about 149.6 million kilometers.
Advanced Usage
- Kepler's Third Law: In celestial mechanics, the square of a planet's orbital period is proportional to the cube of the of its orbit. This law allows astronomers to relate the time an object takes to orbit to its average distance from the star.
Variants and Related Words
- Major Axis (n): The longest diameter of an ellipse, passing through both foci and its center. The is half of this length.
- Semiminor Axis (n): One-half of the ellipse's shortest diameter (the minor axis). It is the distance from the center to the closest point on the perimeter along the shortest line.
- Orbital Elements (n): A set of parameters that uniquely define a specific orbit. The is one of these key elements.
Synonyms
- Mean Distance (n): In the context of astronomy, the is often described as the average or mean distance between two orbiting bodies, though this is a conceptual synonym rather than a precise mathematical one.
Noun
-
one-half the major axis of an ellipse; the distance from the center of an ellipse to one end
