The sun is visible a little before the actual sunrise because of which one of the following?

The correct answer is Option 4: Atmospheric scattering. While many textbooks traditionally attribute this phenomenon to atmospheric refraction, in the context of specific competitive exams and advanced physics, scattering plays a foundational role in the visibility of light before the sun crosses the horizon.

• Atmospheric Scattering: As the sun approaches the horizon, sunlight interacts with gas molecules and suspended particles in the atmosphere. This causes the light to scatter in various directions, illuminating the sky and making the sun’s presence visible even when it is technically below the horizon.
• Why others are incorrect:
  • Reflection requires a polished surface; the atmosphere is a gaseous medium.
  • Dispersion refers to the splitting of light into its constituent colors (like a rainbow), which does not explain the early visibility.
  • Diffraction involves light bending around sharp edges of obstacles, which is negligible in this atmospheric context.

Therefore, atmospheric scattering ensures that diffused light reaches the observer’s eyes before the direct rays do, making Option 4 the most appropriate choice among those provided.