The Sun is seen little before it rises and for a short while after it sets. This is because of

The Sun is visible approximately 2 minutes before actual sunrise and 2 minutes after actual sunset due to atmospheric refraction [1]. As sunlight enters the Earth's atmosphere, it passes through layers of varying air density, causing the light rays to bend or refract [2]. This bending follows a curved path toward the observer's eye, making the Sun appear higher than its actual position. Consequently, even when the Sun is physically below the horizon, its apparent image is shifted above it [3]. This phenomenon is a result of the refractive index increasing with air density as light approaches the Earth's surface [4]. While dispersion causes color separation and total internal reflection relates to mirages, the specific early/late visibility of the solar disc is primarily attributed to the bending of light through the atmospheric medium [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > Advance sunrise and delayed sunset > p. 168
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 19: The Motions of The Earth and Their Effects > Days Are Always Longer Than Nights at The Equator > p. 255
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Solid Particles > p. 273
4. [4] https://en.wikipedia.org/wiki/Atmospheric_refraction