The blue appearance of the sky and the crimson hue of the Sun at sunrise and sunset are direct consequences of the **Scattering of light** by atmospheric gas molecules. According to **Rayleigh's Law of Scattering**, the intensity of scattered light is inversely proportional to the fourth power of its wavelength ($I \propto \frac{1}{\lambda^4}$). Blue light has a significantly shorter wavelength ($\approx 400\text{ nm}$) than red light ($\approx 700\text{ nm}$), scattering nearly 10 to 16 times more effectively across the daytime sky. At sunrise and sunset, sunlight travels through a much thicker layer of atmosphere; shorter blue wavelengths are scattered away from the line of sight, leaving primarily the unscattered longer red wavelengths to reach our eyes.