Twenty minutes after we arrived, we headed to the roof of the dome of the resort. (John has built stairs, which make it accessible. You may just be able to make out the table which is centered at its apex). We settled down with our drinks (rum and coke) from the bar (the arches just below the dome is the restaurant and bar) and waited. We chatted, recounting the day's events, and waited for the Green Flash.

The green flash is a phenomenon that occurs sometimes when the sun sets over a body of water, just as the top of the sun disappears below the ocean. It's not known what causes it, but it is real and it can be photographed. It lasts for about one-half second. We were very lucky to observe it just half an hour after our arrival at John's resort. We named the top of the dome the 'Green Flash Lounge'.

For several days afterwards, we congregated at the top of the Green Flash Lounge at sunset in hopes of seeing it. But we never saw it again, in its full splendor. There was some difference of opinion amongst us as to whether it occurred again. But the first time was real. and it was strong. We would talk about it many times after that. During other days, we often sat in the Green Flash Lounge, observing the birds, the whales and the ships passing by on the horizon.

What causes it?          ~~~ Email ! ~~~ 

Sender: aty@aty486.sdsu.edu

Date: Fri, 06 Sep 1996 21:56:56 -0700
From: "Andrew T. Young" 
To: INFO@NOWSCAPE.COM
Subject: green flash

Nice to see your green-flash report.  Maybe the one you saw lasted 
half a second; the average of several hundred timed observations is
about 2 seconds.  The first time you see one, it's hard to judge,
because the appearance is so startling.

It's actually known what causes the flash, but the causes are complex.
First, refraction in the Earth's atmosphere separates read and green
rays slightly near the horizon.  The intermediate colors (yellow and
orange) are largely absorbed by ozone; and blue is scattered out by the
air itself (that's why the sky is blue).  The red image sets first,
leaving the green.  The separation of the two images depends on the
thermal structure of the lower atmosphere, which is why the flash
sometimes appears and sometimes does not.  Mirage conditions favor the
flash.

There's also a physiological effect in the eye that enhances the green
color at sunset, after you've stared at the red setting Sun for a minute
or two.  That causes a yellow flash that commonly precedes the green one
to appear green, itself.  That's why many photographs jkust show yellow
and not green.  And even the best photographs don't show the glorious
green you see with your eye.

There are additional minor details I could go into, but those are the
main effects.  I'm trying to find financial support for the work I'm
doing on green flashes, but I can't seem to get a nibble from the
standard funding organizations like the National Science Foundation.
Want to sponsor some research?

		-- A.T.Young	  (aty@mintaka.sdsu.edu)

        ----------------------------------------------------------


There's a picture I took that's posted on the Web at

	http://www.isc.tamu.edu/~astro/research/sandiego.html

which was scanned in by George Kattawar's student Dan Bruton.  You probably
should ask for their OK before posting a copy.  Kattawar is

	 kattawar@silly.tamu.edu

and Bruton is

	 WDB3926@acs.tamu.edu

You can tell them I said it's OK.  If you want to go to higher resolution
and scan in a good photographic print or transparency yourself, then I'd
ask for some payment for the use of an earlier-generation copy.

There's a lot of work that can be done with the existing published
sources.  Pieter Feenstra Kuiper's thesis contains hundreds of
observations, with the date and place of each.  He thought he'd detected a
(weak) correlation of the visibility of flashes with atmospheric water
vapor; but in fact the major absorber in the important spectral region is
ozone.  There are good models available that describe the latitude and
seasonal dependences of the ozone thickness; so I think it would be useful
to try to relate the observations to ozone, using the ozone models to
estimate the likely ozone thickness from times and dates.

There's also good evidence that the physiological adaptation effect I
mentioned is important in affecting the colors reported by visual
observers.  This is a slightly touchy area, because a different
physiological effect (afterimages) has been repeatedly proposed, and
repeatedly refuted by (a) observations of flashes at sunrise, and (b)
color photographs.  Furthermore, many physical scientists are upset at the
thought of such "subjective" effects, especially when the visual
impression is so striking.  Nevertheless, this adaptation effect has been
known for over a century in the physiological optics literature, and is
easily demonstrated by staring at a bright red light for a minute or two,
until its color appears orange rather than red.  Then the monochromatic
yellow-orange low-pressure sodium-vapor street lights we have around here
(San Diego) appear a striking yellow-GREEN!  It's clear that this
adaptation effect has influenced many of the green-flash reports in the
literature, and accounts for yellow-orange color photos of flashes that
appeared bright green to the photographer's eye.

I need to spend some time collecting the published evidence and writing it
up, in this case, for publication in a journal like "Applied Optics" which
covers the optics of vision as well as physical optics).  Unfortunately,
I'm practically unemployed (San Diego State pays me 0.2 of a salary for
teaching one course at present), so I'm trying to dig up enough money to
live on while I do the work.

My sunset photography has been supported for the last year or two by
working as a consultant to George Kattawar on a Navy contract.  The Navy
wants us to use the photographs to determine the thermal structure in the
lower atmosphere.  I don't think they are interested in green flashes;
I've come across a lot of interesting information on the flashes as a
by-product of this consulting work, but I'd like to be able to send a
considerable amount of time on the problem and do it right.

If you're interested, I can send you a preprint of a paper we have at
Appl.Opt. in the refereeing process right now.  In it, we describe the
optics of one type of green flash that was previously unrecognized.
However, the green flash is just mentioned in passing in this manuscript.
It deserves a good paper (or a series of papers) on its own.

		-- Andrew T. Young