Why does the color of the moon change? What makes the moon look red sometimes?
Dear Eric, The atmospheric optics rules that you know about for the sun also apply to the moon (and any other object at great distances from the observer) – the sun is just a lot brighter than anything else. The tiny aerosol particles that float in the air are of such a size that they preferentially scatter shorter (“blue”) wavelengths of light out of the line of sight between an observer and an object, compared to longer (“red”) wavelengths. The longer the path through the atmosphere and/or the heavier the load of aerosols, the more scattering that takes place, causing the object to appear more red and less blue. When the object is directly overhead, the path through the atmosphere is as short as possible, and it gets progressively longer as the object sinks toward the horizon. Heavier aerosol loading can be caused by blowing dust, fires, ordinary pollution, and so on, as well as humid conditions that tend to plump up several classes of aerosol particles. So, just as with the sun, you
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