The orbit of a celestial object with respect to the body it is orbiting. The Moon and Earth perform elliptical orbits about their centre of mass, a point about 1600 km below the Earth’s surface. The Moon’s relative orbit about the Earth is of the same shape, but with the Earth’s centre at a focus of the ellipse. Similarly, the planets have relative orbits about the Sun and each component of a binary star has a relative orbit with respect to the other.