科学素养与现象阐释·英语30篇（5）

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为什么彩虹常出现在雨后

Rainbows form when sunlight undergoes internal reflection and dispersion inside spherical water droplets suspended in the atmosphere.
Post-rain conditions provide the optimal combination: abundant falling droplets and concurrent sunlight—usually from a clearing sky.
Droplet size distribution determines rainbow sharpness: uniform 0.5–2 mm spheres yield vivid arcs; mist creates broad, washed-out glows.
The primary bow appears at 42° from the antisolar point—requiring observer, sun, and rain to align precisely in three-dimensional space.
Secondary rainbows form from two internal reflections, appearing fainter and reversed in color sequence at 51° elevation.
Urban light pollution suppresses rainbow visibility, making them rarer in megacities despite frequent showers.
Aerosol loading from pollution or wildfires scatters light, reducing contrast and often eliminating the supernumerary fringes.
Polarization measurements confirm rainbow light is partially linearly polarized—evidence of its reflection-dominated origin.
Mountainous terrain enhances occurrence by triggering orographic lift and localized convective showers.
Meteorologists now use rainbow geometry in lidar calibration to validate atmospheric particle sizing algorithms.
Its transient beauty masks a rigorous optical geometry—governed by Snell’s law and ray tracing mathematics.
Recognizing this phenomenon cultivates attention to light–matter interaction as a daily observable physics lesson.