Ontario Grade 9 Science Class Practice Exam

Retrograde motion refers specifically to the apparent backward (westward) movement of planets in the sky, as observed from Earth's perspective. It is a result of the differing orbital speeds and paths of Earth and the planets, and does not refer to a specific type of body or object like a cloud of dust and gas (A), small body (C), or the mass of an atom (D). Therefore, these options are incorrect in relation to the question about retrograde motion.