🚀 go-pugleaf

In article <2A6DEF17.1804@ics.uci.edu> bvickers@ics.uci.edu (Brett J. Vickers) writes:
>peterk@public.sub.org (Peter Kittel) writes:
>>Is it only me or does the sky beneath a rainbow also appear lighter
>>to others than the sky above a rainbow (or wait, was it the other way
>>around?)? But anyway, for my eye there is definitely a jump in
>>brightness of the background sky (normally rain clouds) from beneath
>>to above the rainbow. Any explanation for this?
>
>Optical illusion?  Two fields of the same color, separated by a line
>of a brighter or darker color, give the optical illusion that one half
>is lighter than the other.  The trick is to cover the line and see that
>they are the same.  I've never tried this with a rainbow.
>
>--
> ___            _    _     _  _        _
>(  _) ___ ___ _( )__( )_  ( )( ) o  __( ) _  ___  ___  ___
>(___)(_) (__=) (_)_ (_)_   (__) (_)(_((_)(_'(__=)(_) _(_)
>Brett Vickers (bvickers@ics.uci.edu)

	It is not an illusion, actually it is even more pronounced
	on a photography of rainbows. A set of rays impinging on
	a raindrop and reflected once inside the drop is "bunched"
	in a certain angle, giving rise to the primary rainbow.
	Rays reflected twice inside the drop give rise to the
	secondary rainbow and so on, as explained in earlier posts.
	With this in mind it is then not too hard to understand
	why there is a dark band between the primary and the
	secondary rainbow.

	For this handwaving explanation of the rainbow it is
	not necessary to assume that the raindrops are spherical.
	I read somewhere that raindrops actually are shaped more
	like hamburgerbuns. It would be an interesting problem
	to try to calculate the shape of a raindrop from a given
	rainbow, then again inverse scattering isn't my strong side.

					Cheers, mw
-- 

-----------------------------------------------------------------------------
	Mattias Waldenvik			Phone:	intl.+46 18 303674
	Swedish Institute of Space Physics	Fax:	intl.+46 18 403100
	Uppsala Division
	S-755 90 Uppsala, Sweden		mw@irfu.se
-----------------------------------------------------------------------------