Red moons

[Mister Emu]

What exactly causes a red moon?

 

[Circle_One]

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 see a dim, red moon on the horizon in conditions of gunky, humid air, and a bright, whitish moon well overhead on clear winter nights. By the way, the optics rules also let the moon create the same optical phenomena as the sun, including rings around the moon, "moon dogs," and rainbows. However, since the moon is much dimmer than the sun, all of these optical effects are much dimmer.

I notice that this is in Science vs. Religion. This is a scientific answer to the question, though there are many different religious meanings for the Red (Blood) Moon. Is that what you want? Or are you looking for a bit of both?

 

[Mister Emu]

Thanks.

I was wondering the scientific reasons.