__________ refers to any of several slow changes in an astronomical body's rotational or orbital parameters. An important example is the steady change in the orientation of the axis of rotation of the Earth.

• A. Nutation
• B. Precession
• C. Eccentricity
• D. Obliquity

Answer: (B)

Precession is the slow reorientation of a body's rotation axis over long timescales. For Earth, gravitational torques from the Sun and Moon on Earth's equatorial bulge cause the axis to sweep out a conical path in space, steadily changing its orientation with a period of about 26,000 years. This matches the idea of a gradual change in rotational parameters, and exactly describes the steady shift of Earth's axis orientation mentioned in the prompt. Nutation is a smaller, shorter-term wobble layered on top of this gradual motion, while eccentricity refers to how stretched the orbit is and obliquity to the tilt of the axis relative to the orbital plane; both are distinct slow changes but do not capture the long-term directional reorientation that precession describes.