Sunsets look red and orange because sunlight travels through much more atmosphere than at midday.

This phenomenon is primarily caused by Rayleigh scattering, named after the British physicist Lord Rayleigh who published his findings in 1871. As sunlight enters the Earth's atmosphere, it collides with gas molecules and scatters in all directions. Blue light has a shorter wavelength and scatters more easily, which is why the sky appears blue during the day.During sunset or sunrise, the sun is at a low angle, forcing the light to travel a much longer path through the atmosphere to reach an observer. In fact, the light may pass through up to 40 times more air mass than when the sun is directly overhead. This extended journey filters out almost all the blue and violet light, leaving the longer-wavelength reds and oranges visible.The intensity of these colors can be further enhanced by Mie scattering, which occurs when larger particles like dust, pollen, or water droplets are present. These particles are particularly effective at scattering light toward the red end of the spectrum. Volcanic eruptions, such as the 1883 explosion of Krakatoa, have historically produced some of the most vivid sunsets ever recorded due to the massive injection of aerosols into the stratosphere.