Here's why:

* Refraction bends light: As sunlight enters the Earth's atmosphere, it passes through layers of air with different densities. This causes the light to bend, or refract.

* Sun appears higher: This bending effect makes the sun appear higher in the sky than it actually is, especially near the horizon.

* Extended sunrise and sunset: Because the sun appears higher, it takes longer for it to rise completely above the horizon in the morning and longer to fully set below the horizon in the evening.

In short, atmospheric refraction effectively "stretches" the daylight hours by making the sun appear above the horizon for a longer time.