I have read the article by Andrew Young about the green flash – Zenit June '99 p. 249 et seq. – with particular interest, because I have often listened to the therein mentioned and cited Dr. P. Feenstra Kuiper when he appeared as speaker for the Alkmaar division of the NVWS, in the '50s. One of his lectures there was devoted to the green flash, although he himself called it ‘the green ray'. This was the subject of his doctoral dissertation. Young mentions that this thesis added hundreds of observations of the green flash to the available literature, without there being one observation of Feenstra Kuiper's own. That may be so, but lest this give rise to the suggestion that Feenstra Kuiper never observed a green flash or green ray himself, the following can serve as a correction.
In his lecture before the Alkmaar division, he said that during the First World War he had been mobilized as a serviceman in the Coast-guard at Callantsoog. On guard at the locally well-known Lookout Dune post, he had repeatedly observed the green ray. Many years later, with company present at a local restaurant, he told that to his dinner guests, who reacted somewhat incredulously. Whereupon they resolved to ‘put the sum to the test’ and climbed the Lookout Dune together as sunset approached, seeing as the weather conditions were favorable for the observation of the green flash or ray. And indeed: the company saw what Feenstra Kuiper had seen there repeatedly. ‘I was the hero of the day,’ according to Feenstra Kuiper during his lecture in Alkmaar.
According to Young, Feenstra Kuiper concluded in his thesis ‘that a high humidity in general is conducive to the phenomenon'. Possibly here he alluded to observation of the green ray instead of the flash, as the green ray arises by ‘forward scattering by haze particles’ as Young describes on page 254. Feenstra Kuiper emphasized during his lecture at Alkmaar that the green ray appears when the Sun sets as a yellow disk. I think that this is the case when relatively little moisture is found in the atmosphere at the place of observation. Feenstra Kuiper also said at Alkmaar that the phenomenon of the green ray can appear during rising and setting of the full Moon, if the relevant horizon were formed by the sea surface.
En passant he mentioned further that Jules Verne has devoted one of his books to the green ray, but that the original title Le Rayon Vert in the Dutch is mistakenly translated as De Wonderstraal [“The miraculous ray”]. Which indeed it is. The adventurers in the book, in order to be able to behold the ‘Wonderstraal’, act so that at the crucial moments the observation, by circumstances, always fails. In my personal case is that also so. There were the always the wet air and a ‘dirty’ horizon which have withheld from me the phenomenon of the green flash or green ray. But the lecture of Dr. Feenstra Kuiper is for me unforgettable. That compensates for the loss.
Cor Booy, De Rijp.
I am delighted to hear that my suggestion that Feenstra Kuiper had never seen a green flash has been corrected. It's a great story! There are many cases known of green-flash observations that were skeptically received by people who themselves had never seen one. So it is good to hear that there are also cases in which the flash appeared ‘on command.’ That this has happened under the supervision of Feenstra Kuiper is really splendid.
Translations © 1999, 2005, 2006 Andrew T. Young