[Tfug] Another OT Optics Question

[Jeremy D Rogers]

[snip]
>> And, the apparent "diameter" of the rainbow is a function
>> of how far the water is from the observer?  E.g., a rainbow
>> thrown from the mist of a gargen hose would appear to have a much
>> smaller diameter than one from water vabor many miles distant.
>
> I think that the *angular* diameter remains the same, tho, obviously,
> the actual refraction-reflection-refraction is occurring much closer
> than if the drops were from a distant rainstorm.  And, because the sun
> is presumably 'way above the horizon, the the arc of the spraybow would
> be less than a semicircle.  In fact, if the sun is more than 42 degrees
> above the horizon, a rainbow is impossible (because its "center" is more
> than 42 degrees below the horizon.)

I think Hu's right, but just to be clear, if the 'angular' size is
always ~40deg, then it always appears the same size. Looking at a
rainbow formed by the mist of your garden hose (which could be a full
circle since the mist can be between you and the horizon), you might
be fooled into thinking it looks smaller because the stuff next to it
is closer, but in terms of angles, it's the same.

>> (I'm not looking for "6 decimal places", here... just a crude
>> understanding of the geometry involved  :>  )
>>
>> Thx!
>> --don
>>
>>
> Regds,  Hu Bath
>
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