Re: [Leica] Measured Reaction Time / Marvin / Alf / Dave

[Dennis Painter <dwp@deltanet.com>]

Alan,

I dropped the following into excite search:

 "green flash" sun

The first url that came up was:

http://www.phy.mtu.edu/apod/ap970909.html

This is "The Astronomy Picture of the Day" and an explaination of "The
Green Flash"

Isn't the web great! ;-)


Dennis


Alan Hull wrote:
> 
> Ted and Donal,
> I spent a week capturing the mythical green flash, from a beach in the
> Carribean.  My technique used the curvature of the earth to assist reaction
> times.  I only tried it with sunsets, in fact I didn't know it was also
> present at sunrise.  Apart from that, my yacht and the beach were on the
> west side of the island, so sunsets were what I had.  From the beach, if
> you sit on the sand, the horizon is about one mile away.  if you stand up
> the horizon is over two miles away.  Thats the key.  Set the camera up on a
> high tripod,  then sit on the sand (a chair is more comfortable).  When you
> see the green flash, release the shutter.  You can calculate the difference
> in time if you want to make your head hurt,  refraction complicates the
> equation, or you can experiment.  Wait for the rim of the sun to kiss the
> horizon then stand up and count the seconds until it happens again.
> 
> Did I succeed.  Dont know.  Because of the humidity I stored the film in a
> tin surrounded by dry tea leaves.  That tin and a whole heap of tinned food
> was stolen from the boat a few days later.  I was lucky because the cameras
> and radio gear were not even disturbed.
> 
> When I discussed this with a boffin in a white coat with his top pocket
> full of pencils he told me the green flash was only a sensory thing caused
> by the sudden removal of a bright red sun from the retina of the eye,
> causing a neuron backlash.
> 
> One day I will try again.  Dont forget the ND filters over your eye.  I
> used sextant shades.
> 
> Alan Hull


- -- 
Experience is a tough teacher. It gives the test before the lesson.
- -unknown