A star near the horizon appears to be at a position slightly higher than its actual position in the sky. Using the concept of atmospheric refraction, explain why this happens.
Generated by claude-sonnet-4-6 · 2026-06-26 01:09 · grounding rag
Model Answer
When starlight travels from outer space into Earth's atmosphere, it passes through layers of air with gradually increasing density (and refractive index). As the atmosphere bends light towards the normal (from rarer to denser layers), the light rays curve continuously. For a star near the horizon, this bending is more pronounced because light travels through a thicker layer of atmosphere. As a result, the apparent position of the star — where the refracted ray seems to come from — appears slightly higher than its actual position in the sky.
Source: Chapter 10, Section 10.5 – Atmospheric Refraction
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Explanation
- Key concept to state: Atmospheric refraction occurs because air density (and refractive index) increases gradually from top to bottom.
- Direction of bending: Light bends towards the normal as it enters denser layers → overall path curves upward → apparent position shifts higher.
- Why near horizon: Light travels through a greater thickness of atmosphere, so the effect is stronger near the horizon.
- Examiners look for: mention of gradually changing refractive index, bending towards normal, and the conclusion that apparent position is higher than actual. Three clear points = 3 marks.