Science (086) — AI-generated practice question

Stars twinkle because of atmospheric refraction of starlight. As starlight enters the earth's atmosphere, it passes through layers of air with continuously changing refractive indices (due to varying temperature and density). This causes the path of light to keep shifting slightly.

Since stars are extremely distant, they act as point-sized sources of light. Even a tiny shift in the light path causes the amount of starlight reaching our eye to fluctuate — making the star appear sometimes brighter and sometimes fainter. This flickering is perceived as twinkling.

Source: Chapter 10, Section 10.5 — Atmospheric Refraction

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Examiners look for three specific points (one per mark):

1. Cause — atmospheric refraction through layers of varying refractive index/density.
2. Effect — continuously changing path of starlight → fluctuating amount of light reaching the eye.
3. Nature of stars — point-sized (very distant) sources, so no averaging-out occurs (unlike planets).

Avoid writing too much about planets unless specifically asked — it wastes time. The phrase "point-sized sources" is key terminology the examiner expects.