The Moon and Sky

The other night, Kim noticed that the moon was huge and orange on the horizon.  I wanted to take some photos, but by the time I was able to get to a location with a low enough view of the horizon, the hugeness and orangeness were gone.  I snapped a few photos anyway, and I don’t think they’re great, but here are 3 of the best ones.

These are all unedited except for lossless cropping, and all were taken with my Sony DSC-S85 set to 3x optical zoom, and with my Kenko Tele Converter KUT-500 5x zoom lens attached.

The moon appears to be orange when it’s right on the horizon because the light is travelling through more air than when the moon is high in the sky.  When the light collides with molecules in the air, the molecules steal some of the light’s energy, and this happens most readily at the blue/violet end of the spectrum because of an obscure inverse-quad law.  Anyway, when the moon is overhead, its light isn’t passing through enough air to strip out all of the blue energy, so the light that makes its way to us still appears white.  But when the moon is on the horizon, its light has to travel through a lot more air to get to us, so many more collisions take place causing much more blue energy to be stripped out, leaving mainly the orange/red hues to reach our eyes.  This phenomenon also explains why you can get sunburn during the day but not around dusk or after: ultra-violet light, being at the short-wavelength end of the spectrum, is the first to be stripped out.

(And it also explains why sunset skies are red and orange.  It is a myth that pollution causes pretty sunsets -- in fact, pollution diminishes the vibrancy of such colorful skies.)

But all that to say this: why isn’t the moon huge and orange on the horizon every night?  Or is it so, and I just don’t see it?  I definitely don’t see the moon every night, nor indeed that often at all, but I can only recall a handful of times that I’ve seen it huge and orange.

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