This question relates to the exact meaning of "optical". I would normally say that optics refer to phenomena caused by the behavior of light through different media, like reflection, refraction, diffusion, and so on.

However, I recently read about auroras being referred to as an optical phenomenon. I thought that strange, since auroras arise due the interaction of cosmic particles and air, simply emitting light at the right places, and is pretty much entirely unrelated to any breaking of the light.

But I couldn't really protest since I'm not sure that my naïve understanding of "optics" is correct. What say you?

  • 1
    Sounds like they were using optical to mean visual. This is sometimes done, as in optical illusion (which is really a neurological effect in the visual areas of the brain, not something related to the light itself).
    – Barmar
    Commented Nov 4, 2014 at 17:11
  • 2
    Aurora are more commonly referred to as an atmospheric phenomena. Commented Nov 4, 2014 at 17:16
  • Well, it generally counts as a phenomenon, and without the optics of your eyes you would not see it. It is not, however, an "optical illusion". But scientifically there are probably several other "phenomena" it would probably classify under sooner.
    – Hot Licks
    Commented Nov 4, 2014 at 17:32

1 Answer 1


Here are relative prevalences in Google Books for some different possible associations...

aurora "electromagnetic phenomenon" 96 hits
aurora "visual phenomenon" 99 hits
aurora "solar phenomenon" 320 hits
aurora "optical phenomenon" 588 hits
aurora "atmospheric phenomenon" 1100 hits

I think what that tells us is that regardless of any distinction OP may draw between visual and optical, most writers prefer the latter when referencing aurora.

Personally I don't recognise OP's distinction as meaningful anyway. Obviously optical illusions don't usually involve "the behavior of light through different media", but as this GoogleFight shows, they wipe the floor with visual illusions.

  • Thanks for an interesting answer. However, I don't really think a popularity contest answers the question, as people are at times known to be wrong. :) I cannot help but suspect that this is rather a mistaken conflation of "optical" and "atmospheric" phenomena due to the fact that so many of the latter are of the former kind.
    – Dolda2000
    Commented Nov 4, 2014 at 20:34
  • The point about optical illusions is certainly interesting, however, but it rather leads me to think that a more proper distinction is that optical phenomena are those that makes you see things that aren't real (though the phenomenon is still objective, unlike eg. hallucinations), and that the field of optics might then rather refer to the study of the causes of such phenomena.
    – Dolda2000
    Commented Nov 4, 2014 at 20:34
  • Well, terms like electromagnetic, atmospheric are "orthogonal" to visual, optical in the first place - I only listed so many to show that there are a variety of different usages out there. But as regards what seems to be your substantive point (you think people should refer to aurorae as visual rather than optical phenomena) I think an almost 6:1 preference against it has to carry the day. If that large a majority people are "wrong", you have to redefine your concept of right/wrong. Commented Nov 4, 2014 at 21:25
  • I never did say anything about "visual". My question only pertained to whether "optical" is appropriate. :)
    – Dolda2000
    Commented Nov 4, 2014 at 21:26
  • Sorry - I must have seamlessly moved from your text to @Barmar's comment, then I got carried away because (as I expected) it was so easy to establish a strong preference for optical over visual in respect of illusions. On the semantic front, I think you're attaching too much significance to the specialised domain-specific noun usage optics = the branch of physics that deals with the properties and phenomena of light. That's from the OED definition, btw, which continues with ...sometimes esp. in relation to sight. Imho, it's "appropriate" in your context. Commented Nov 4, 2014 at 21:40

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