radius vector

noun, plural radii vec·to·res [vek-tawr-eez, –tohr-] /vɛkˈtɔr iz, -ˈtoʊr-/, radius vectors.

1. Mathematics. the length of the line segment joining a fixed point or origin to a given point.
2. Astronomy.
   1. the straight line joining two bodies in relative orbital motion, as the line from the sun to a planet at any point in its orbit.
   2. the distance between two such bodies at any point in the orbit.

noun

1. maths a line joining a point in space to the origin of polar or spherical coordinates
2. astronomy an imaginary line joining a satellite to the planet or star around which it is orbiting

1. A line segment that joins the origin and a variable point in a system of polar or spherical coordinates.
2. The imaginary straight line that connects the center of the Sun or another body with the center of a planet, comet, or other body that orbits it.