Thank you Doug, thank you naturerecordists, and especially those who
responded to my plea.
janet lowry has certainly come up with the important information I wanted,
in her quote from the New Scientist web site.
Chris Owen's suggests "St Elmo's fire", and it is likely that was the name =
I
read long ago, but it seems that it really refers to a different kind of
phenomenon - electrical discharge rather than light diffraction.
J. Young, in nominating St Elmo says "Remember Moby Dick?" I do remember
that as the name of a famous book - which I've never read, alas.
So I don't have a Saint's name for the green flash, but now I do know what
it is, and how it is caused. And it seems reasonable to assume that in fac=
t
it does not have a Saint's name at all, or New Scientist would have used it=
.
Again my sincere thanks to all.
Syd
(The internet is gradually turning humankind into one gigantic brain with
virtually limitless potential ... if said brain can cure certain malignant
tumours before being destroyed by them!)
> From: jplanet10 <>
> Reply-To:
> Date: Fri, 13 Feb 2004 14:57:30 -0800 (PST)
> To:
> Subject: [Nature Recordists] Re: Saint Who's fire?
>
> I don't have any old issues of Sky and Telescope
> handy, but I did find the following article on the New
> Scientist web site.
>
> Cheers,
>
> janet lowry
>
> "Question
>
> Whatever happened to the famous but rare "green flash"
> we used to hear about so often twenty or so years ago?
> Observers reported a momentary but brilliant green
> appearance of the Sun as it sank below the horizon,
> usually over the sea in tropical climates. Sometimes
> the whole sky turned green as well. Was this green
> flash real, and if so, what caused it? Why is it so
> rare, has it been recorded on film and where are the
> best places for seeing it?
> Tim Conway , Upwey Victoria Answers
>
> The green flash is caused by different amounts of
> refraction in the Earth's atmosphere. Rays of blue
> light are bent more than green, rays of green are bent
> more than yellow, and rays of yellow are bent more
> than red.
>
> This refraction raises the apparent altitude of a
> celestial object such as the setting Sun, because the
> difference between red and green rays is about a
> minute of arc at the horizon. Therefore the upper part
> of the setting Sun has a green fringe. If the air is
> very clear and the horizon is sharply visible, the
> green fringe will be all that is visible of the
> setting Sun for a second or two as the Sun vanishes
> over the horizon, causing the distinct green flash
> referred to above. The flash can also be seen at
> sunrise if you know exactly where the Sun will appear.
>
> The air must be completely free of haze and cloud
> between the observer and the setting Sun in order to
> witness the phenomenon, a condition that is rarely
> met, which is why few people have seen the flash.
>
> Under very favourable conditions, the even rarer blue
> flash can be seen in which the green shade appears to
> slide swiftly up the spectrum into a pale blue speck
> just before the Sun disappears completely over the
> horizon. Blue light is bent more than green light and
> so this phenomenon is witnessed immediately after the
> green flash and just before the Sun vanishes.
>
> I saw several green flashes in 1995, either from a
> mountain-top observatory (where a momentary blue flash
> was visible) or from sea level looking out over the
> ocean. Reports that the whole sky turned green are
> unlikely to be true; the flashes are not especially
> bright, and afterimages from the dazzling pre-flash
> setting Sun can make it hard to see the flash well.
>
> The total light from the green flash itself has been
> estimated to be about the same as from the planet
> Jupiter at opposition.
>
> Green flashes are reported more frequently in tropical
> regions or coastal areas because this is where the
> likelihood of a long clear air path is the greatest.
> But, given the right weather conditions, they can be
> seen anywhere.
>
> A few years ago volcanic dust from the Mount Pinatubo
> eruption reduced the clarity of the atmosphere to such
> an extent that green flashes were rarely seen, but
> most of the dust has since dispersed and they are
> visible once again.
>
> Taking photographs of the green flash requires some
> special camera equipment, such as a telephoto lens and
> a tripod, but not many people bother and this explains
> why photographs of the phenomenon are rare. An example
> was published in the astronomy magazine Sky and
> Telescope in 1994, and I have also found a number of
> earlier ones.
>
> Mike Dworetsky , Department of Physics University
> College London"
>
>
> _______________
>>
>> Message: 16
>> Date: Fri, 13 Feb 2004 20:36:00 +1000
>> From: Syd Curtis <>
>> Subject: Saint Who's fire?
>>
>>
>> Doug,
>>
>> Please grant me the indulgence of one
>> off-topic question.
>>
>> In my posting about Lord Howe Island and its so
>> friendly birds, I mentioned
>> seeing St Anthony's Fire from a LHI restaurant.
>> Martyn Stewart very rightly
>> asks,
>>>
>>> Lastly, what the hell is St Anthony's fire? Is
>> this the equivalent of our
>>> northern Lights?
>>>
>> I confidently turned to my Scientific Dictionary to
>> give him an
>> authoritative answer only to find that I've got the
>> wrong name. The
>> Dictionary refers to something completely different
>> for St Anthony's fire.
>> And worse there was no indication of the right name
>> among the Saints.
>>
>> Somewhere years ago, I read of the phenomenon of a
>> flash of green light,
>> just at the moment when the upper edge of the sun
>> finally disappears below
>> the horizon at sea. My recollection is that one had
>> to be in fairly high
>> latitudes to get this, and therefore I was both
>> surprised and delighted when
>> watching the sun setting from the restaurant at
>> Capella South on LHI to see
>> a very definite green flash.
>>
>> Now it will annoy me until I can find the right
>> name. PLEASE, someone on
>> naturerecordists, which Saint's name should I have
>> been using? And if you
>> can tell us what causes it, so much the better.
>>
>> TIA
>>
>> Syd Curtis (Brisbane, Australia)
>>
>>
>>
>
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