Green Phenomena at Sunrise and Sunset
green flash , green ray , green dot , green shift , green segment , green glow
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Updating the preliminary page which formerly appeared here has
already taken too long to complete .
So , this temporary , intermediate page is now here to make
several important points and provide a link to the previous ,
preliminary version .
Compared to the usual confusing and commonly utterly inaccurate
accounts found in reports of observations , respected textbooks ,
and on a variety of wonderful and mediocre websites , the account
here makes several important points , apparently never previously
seen together .
( a )
The Green Flash is an exceptional , mind-boggling , rare ,
poorly-understood sight of Sunrise and Sunset .
The true and legendary Green Flash seems as bright as a flashbulb
and has the same momentarily disturbing effect on vision .
It has been compared to a lightning strike .
Hypothetically , there may be different types of green flashes .
It is so rare that I am unaware of any image which captures it .
( b )
That's about it for the definite article "the" .
Well , not really , but one of the persistent myths is that all the
various green phenomena seen at Sunrise and Sunset are minor
variations of the same basic phenomenon .
That's not true .
Prof. Andrew Young has documented on hundreds of pages at :
http://mintaka.sdsu.edu/GF/
that a number of quite different optical , atmospheric and
meteorological mechanisms combine in various ways to produce
effects of various types , events of different character .
In particular , referring to the whole subject or the range of
phenomena as "the green ray" or "the green flash" or
"le rayon-vert" or "der grne Strahl" is horribly misleading .
And produces a very troublesome ambiguity .
It is a major disservice to beginners .
And a real discouragement to photographers and imagers who may want
document the various phenomena .
There is a clear need for high quality documentation .
Mea culpa : I've previously made this same mistake like everyone
else ; and editing out the inappropriate definite articles will
be an important task .
( c )
A caution .
Don't be fooled into confusing the green flash with the "ordinary"
bright green dot displays , including the green shift =
green segment = green glow .
Green dots and the green flash are both bright and remarkable
sights .
There is a difference between green dots and the green flash .
Green dots are , roughly , of normal photospheric brightness .
The green flash is an immensely brighter burst ,
seemingly 10 or 100 times brighter .
The experience of observing a green flash is qualitatively
different than the much more common experience of observing green
dots .
James G. Wood recognized this point in
"The Green Flash" , "Symons's Meteorological Mag." V53p99 , 1918 :
"If we are to arrive at a satisfactory explanation, we must
carefully distinguish the two phenomena."
Mulder repeatedly emphasized the various types then known in his
book in 1922 .
Indeed , the mechanism which produces the green shift is utterly
incapable of producing a green flash .
Mathematical nomenclature : A chord cuts off an arc from a circle
and , simultaneously , cuts off a segment from the disk enclosed by
the circle .
Application : Ideally , a spherical sun rises above a horizontal ,
linear horizon to expose a segment of itself .
Reality : Atmospheric chromatic differential refraction , ACDR ,
splits this ideal sun near the horizon into a range of suns of
different spectral colors , conventionally , the red sun below the
orange sun below the yellow sun below the green sun below the blue
sun below the violet sun , although actually , a much larger
range , a more or less continuous range , is present to a certain
extent on various occasions .
At Sunset , after the yellow sun sets , the remaining
segment of the photosphere may be revealed as a surprisingly bright
green color .
( d )
Lack of continuity of the spectrum .
In the phrase above , "a more or less continuous range , is present
on various occasions" , the key phrase is "on various occasions" .
I have seen the first bright bit of the Sun vary widely in color ,
from far over toward red to far over to blue .
Sometimes 2 or more colors are visible from the Sun during the same
Sunrise .
What I have not seen , and have not seen reported , is a continuous
spectrum .
See the spectra on p. 61 of Minnaert's book ,
"The Nature of Light and Colour in the Open Air" .
There seems to be , at the very least , a strong tendency toward a
few discrete colors , and not a smearing , not a continuous
spectrum , not even a continuous spectrum spread out during an
interval of time . Solar spectra taken as higher altitudes are
substantially continuous , so this discreteness must arise from
atmospheric modification along the long horizontal path .
For more details on various colors at Sunrise or Sunset , take the
link near the bottom of this page .
( e )
Green rays , as described by Mulder in his book in 1922 , pp. 3-6 ,
10 , 17 , 21 , 36-37 , 94 and 96 , especially pp. 4 and 96 ,
and by Young ,
http://mintaka.sdsu.edu/GF/observing/greenray.html
apparently are a distinct , exceptional phenomemon which is rare .
( f )
Immediate , dramatic color change at the chromosphere
Often , the color of the first bright bit of a Sunrise will vary
immediately and dramatically .
2 or 3 colors may be seen .
E.g. , see the blue Sunrise infra .
These change too rapidly to be timed by stopwatch .
Mulder's mention , p9 , of the chromosphere leads me to suspect
that these rapid changes may well be due to the very brief
appearance of the chromosphere , seen mixing through various
meteorological modifications .
( g )
It seems clear that between the publication of Mulder's book in
1922 and Young's contributions beginning in the '90's , very few
worthwhile publications on the green phenomena appeared .
About 3/4 of a century was mostly lost .
2 more recent observations .
Blue Sunrise .
I've seen a few blue Sunrises .
One stands out .
There was a 3 degree "radius" orange glow about the orient
just before Sunrise on the morning of 2009-09-19 .
The horizontal haze seemed to be light , but the glow implies
moderate .
Like nearly all my observations , the following were made using
7x35 binoculars .
2 minutes prior to Sunrise , a part of the sky ~2 ' high , very
low , ~10 ' left of orient , ~8 ' wide was tinged greenish ,
very pale , weak , but a great contrast to the usual variation of
orange .
The Sun rose behind a distant hill ;
actually the Earth rotated me .
The first bit was a whitish-blue , which instantaneously became
bluish-violet , which immediately became a brilliant "blue-blue"
patch of intense brightness , quickly too bright to look at ,
spreading horizontally with extremely little green .
Green was virtually unseen , the whole event being blue .
Later a tiny speck of green was momentarily seen at the right end .
The blue ended ~7 or 8 seconds after the first bit .
This was a truly spectacular event which revealed that a segment
of the blue sun can be bright enough to overwhelm and force me to
look away .
I looked long enough that it took ~2 minutes afterward for my
central vision to recover .
Usually the extremely bright , overwhelming light which forces me
to look away is yellow or orange .
This was blue , truly a blue Sunrise .
I think when the atmospheric aerosols are sufficently weak this
produces a sufficiently clear path for the blue sun to be seen .
If the aerosols aren't interfering , the blue sun is very bright .
This event was a blue segment , not a blue flash .
The first bit , whitish-blue , appeared 2009-09-19 111433.02 ,
personal equation estimated at .25 seconds not applied .
Large green patch.
This is a phenomenon I don't recall seeing before in any of
many hundreds of observed Sunrises from this location ,
-81.8637 , 41.3735 , 256 m :
2014-03-07 , 2 % cloud cover ,
haze very difficult to judge as cloudiness and
haze varied greatly on a very small scale .
In the 1/2 minute prior to Sunrise , the immediate vicinity of
the orient was very bright orange ;
hard to monitor w/eyeball ; haze at orient may have been moderate
but was possibly as thick as light cloud .
SunRise , behind trees , some nearby some on the far ridge
[ the /3/ , /4/ and /5/ infra denote stopwatch splits ;
I have suppressed the debriefing of the watch and give
only the resulting UTC ,
personal equation estimated at .25 sec not applied
]
/3/ first bit pale yellow 11 55 3.45
[ had green been seen in here , it would have been separately
timed ( as /4/ )
]
/4/ large bright green patch began , ~ 4' high , ~ 6' wide ,
an oval , fairly bloomed outward from a center where there had
been nothing , above brightening orient ,
centered ~ 3' above the top of the Sun ,
green perhaps slightly yellow , but a luminous green , seemingly
"photospherically" bright ,
definitely greenward of yellowish-green .
+11.35 11 55 14.80
/5/ yellow overwhelmed + 3.98 11 55 18.78
The large green patch was whiter near its periphery , i.e. , not as
saturated .
The separation of the green patch and the Sun wasn't anything like
those caused by leaves or branches .
It seemed nothing like a detachment , seeming to be free-standing ,
highly symmetric and smooth , though it didn't have a precise ,
definite edge .
The link :
The preliminary version of this page has been moved to
http://upforthecount.com/astro/greenprelim.html
Prologue
More high-quality data is desperately needed .
Walter Nissen
preliminary posting : 2013-05-08
minor update : 2013-05-11
this intermediate page installed : 2014-03-24