SSC Stenographer 2026 PYQ — Question 2

Solution: The correct answer is Relative planetary motion.
Explanation:
☛ Apparent retrograde motion is the temporary, observed backward motion of a planet across the night sky relative to background stars.
☛ This phenomenon is an optical illusion caused by relative planetary motion, due to differences in orbital speeds and distances from the Sun.
☛ For example, because Earth has a shorter orbit and travels faster than outer planets like Mars, it periodically overtakes them; as Earth passes Mars, Mars appears to reverse its direction against the background stars.
☛ Nicolaus Copernicus successfully explained this phenomenon in the 16th century using his heliocentric (Sun-centered) model.
Extra Exam-Relevant Facts:
☛ Precession: Refers to the slow, continuous change in the orientation of an astronomical body's rotational axis, taking about 25,772 years for Earth (precession of the equinoxes).
☛ Gravitational lensing: Occurs when a massive celestial body's gravitational field bends light from a distant source, as predicted by Albert Einstein's General Theory of Relativity.
☛ Orbital resonance: Occurs when orbiting bodies exert regular, periodic gravitational influences on each other, often having orbital periods in small integer ratios (e.g., Pluto and Neptune have a 2:3 resonance).
☛ Epicycles: In the ancient geocentric system, Ptolemy incorrectly used mini-circles called epicycles to explain retrograde motion.
Important One-Liners for Upcoming Exams:
☛ Who formulated the three laws of planetary motion? → Johannes Kepler
☛ Which astronomer first used epicycles to explain retrograde motion in a geocentric model? → Ptolemy
☛ Which planet has the shortest orbital period around the Sun? → Mercury (about 88 Earth days)
☛ What is the phenomenon called when an inner planet passes directly between Earth and the Sun? → Planetary Transit
☛ Which law states that a planet sweeps equal areas in equal intervals of time? → Kepler's Second Law (Law of Equal Areas)