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Dear mailing list members!
The Danzig display reported by Hevelius in his "Mercurius in Sole visus"
is propably the most famous halo displays of all. One of the reasons is
that he describes a 90 deg. Halo, which is still unexplained. Propably
the 90 deg. Halo was a subhelic arc in reallity.
Some weeks ago I found a book in the Herzog August library of
Wolfenbuettel (Germany) titeled " Siebenfaeltiges Sonnenwunder oder
sieben Nebensonnen, so in diesem 1661 Jahr den 20. Februar neuen Stils
am Sonntage Sexagesima um 11 Uhr bis nach 12 am Himmel bei uns sind
gesehen worden". In English this means : Seven suns seen on Feb/20/1661
from 11-12 o`clock at our sky. The book was published in March 1661 only
one month after the display. It contains a sermon of the Danzig priest
Georg Fehlau. Fehlau preached the text on March 6th in the Danzig
cathedral. This was only 14 days after the halo display. My first
expectation was that this is a so far unknown independent observation of
the Danzig halo display which may solve Hevel`s halo.
Unfortunatly I was wrong. The discription of the display given by Fehlau
is nearly totally similar with Hevel`s. I was wondering first, because
Hevel`s book was published in 1662 about one year after Fehlau`s
publication. Fehlau gives credits in his book to Hevelius and says that
he visited him on March 3th 1661 to observe a comet with Hevel`s
telescope. Probably Hevel showed him his notes of the halo observation
on this day. This means that Hevel wrote down his observation
immedeately after the halo display.
Fehlau describes the 90 deg halo based on Hevel with these words: "...
On this circle (comment: parhelic circle) stood three silver suns. One
in the northwest opposite of the sun, one in the northeast and one in
the southwest. Through the two last gone a piece of a white circles arc,
comming from the top. So that it seemed that there was a white cross
going through the two white parhelia. This cross was very marvelous and
was visible for 1 1/2 hours."
Hevel also mentioned that the pieces of the circle formed a cross with
the parhelic circle. A subhelic arc cuts the parhelic circle under a
small angle and can`t look like a cross. This is an argument against the
opinion, that Hevels halo was a subhelic arc.
Fehlau writes that the whole city talked about the sky appearance in the
last 14 days, still talkes about it and will talk about it in future. At
the end of his writing a drawing of a halo display can be found. He did
not mention this drawing in the text. So it is unsure if this is a
drawing of the Danzig display. It is different form Fehlau`s description
of the phenomenon. I make this drawing temporary available for you on
this site: http://members.tripod.com/~regenbogen/hevel.jpg .
Regards,
Mark Vornhusen
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