Why does the sky appear red and yellow during sunsets.
1. The reds and yellows are caused by the Sun's light having to pass through dust particles near closer to the horizon than when the Sun is higher in the sky.

2. At sunset the prismatic effect of the atmosphere at low angles produces longer red and yellow wavelengths.

3. At sunset blue light is scattered by air molecules at higher altitudes. The longer red and yellow wavelengths must travel further through the atmosphere when the Sun is near the horizon. At some point the reds and yellows finally scatter in the lower atmosphere causing the reds and yellows.

4. The red and yellows are appear at sunset because the light must pass through more atmosphere which slows down the wavelength frequency turning it to slower red and yellow frequencies.