Abstract: By discussing the "the moonlight floats over the wilderness" in an ancient poem, this paper introduces the Tyndall effect in the wild nature and discusses the light scattering phenomena. Furthermore, it analyzes the influence of small particle of different sizes on the light scattering process, which leads to the Mie scattering and the Rayleigh scattering models. It also discusses the application of the Mie scattering and Rayleigh scattering in optical measurements of fluid mechanics, such as the particle image velocimetry and the nano-tracer-based planar laser scattering.