Forrest Mims' Science Experiments

Chapter 10 Build a Twilight Photometer, part 1

Have you wondered why some sunsets are so spectacular and others so drab? This ultra-sensitive photometer project will allow you to tease out the secrets of twilight, and even do serious science by finding the altitude of the dust, smoke, and air pollution that influence the colors of twilight.

With this project you can detect the tiny particles and droplets known as aerosols from 3km (around 10,000 feet) high to well above the top of the stratosphere at 50km (165,000 feet). While the photometer will not detect aerosols below 3km, many of those particles eventually float high enough to be detected. For example, from my Texas site I’ve measured the altitude of smoke from distant fires, haze caused ...