Besides clouds, what factors reduce atmospheric transparency on seemingly clear nights?
Answer
High humidity, airborne dust, wildfire smoke, or industrial haze
Atmospheric clarity, or transparency, is essential because even on a moonless night, poor air quality can negate the darkness. When conditions are seemingly clear of clouds, transparency issues still arise from various microscopic or macroscopic contaminants suspended in the air. These include high levels of humidity, fine airborne dust particles, smoke originating from wildfires, or generalized industrial haze. All these elements contribute to scattering the light traveling from distant stars and planets, which consequently diminishes contrast and blurs the fine details visible through observation.
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