Atmospheric Monitoring with Arduino

Chapter 6. Using the LED Photometer

One of the oldest bits of weather lore is "Red sky at night, sailor’s delight. Red sky in morning, sailors take warning." The sky is often red, or reddish orange, at sunrise and sunset. Reds, pinks, and oranges dominate at these times of day because the distance from your eye to the sun is greater at these times than when the sun is directly overhead. When sunlight travels through the atmosphere—and especially when it travels that extra distance from the horizon—an effect known as Rayleigh scattering takes place.

The British physicist John William Strutt (the third Baron Rayleigh) explained in 1871 that air molecules are so small they interfere with and scatter photons of light. The various molecules that make ...