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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A noon sight conundrum
From: Wolfgang K�berer
Date: 2004 Mar 3, 15:32 +0100
From: Wolfgang K�berer
Date: 2004 Mar 3, 15:32 +0100
Dear George, I am following my tendency to make nitpicking remarks again. In December you commented on early declination tables as follows: "Early navigators went by a set of declination tables that were the same for each year, and accepted the inaccuracy. It was Pedro Nunez in about 1530 who recognised that he could make a more accurate declination table for leap years, another for leap years +1, leap years +2, and leap years +3, and that would be all that was needed, for many years. They became semi-permanent." This is not historically correct: Although the earliest printed navigation manual that we know, the "Regimento do Astrolabio" (ca. 1509) contains tables for the declination of the sun only for one year, the next manual, the "Tractado da Spera" ( ca. 1516) has tables for the leap year and the following 3 years which were probably prepared for the circumnavigation of Magellan. The fact that one has to take into consideration the fact that a solar year does not have exactly 365 days was therefore well known before Nunez to the anonymous author that constructed these tables on the basis of Zacuto`s "Almanach Perpetuum" (Leiria 1496). The most thorough study of the Portuguese manuals can be found in Luis de Albuquerque`s "Guia N?utico de Munique e Guia N?utico de Evora" (Lisboa 1991) and "Astronomical Navigation" (Lisboa 1988). In comparison to these manuals Nunez` works are of a purely theoretical nature; their tables do not contain solar declinations for every day but positions of the sun in the zodiac; one then has to consult a separate table "Tavoa das declinacoes" to find the declination of the sun (cf. Nunez "Tratado da sphera..." Lisboa 1537 fol. E IIII). This was standard astronomical practice for some time by then - Zacuto uses it as well as Regiomontanus. Early last month you remarked in another post: "I have a modern reprint of Matthew Bourne's "A Regiment for the Sea", which, two centuries before the Nautical Almanac, provided Sun declination tables for each day at noon over a four-year cycle starting 1574: taken, I suppose, from Pedro Nunez." William (not: Matthew) Bourne`s "Regiment for the Sea" does contain declination tables for the sun over a four-year cycle as does about every navigation manual in Portuguese, Spanish, French, Dutch, German and English as well as almost all Portuguese Portolan Atlases produced after 1520. It is highly unlikely, though, that Bourne`s tables were derived from Nunez; Bourne certainly knew the English translation of Matin Cortes` "Arte de Navegar", but there is no indication that he read or even knew the works of Nunez - they were printed in Latin and Portuguese. Apart from that Nunez gives as the maximum of the sun`s declination a value of 23 degrees 30 minutes (Nunez "Tratado da sphera..." Lisboa 1537 fol. E IIII), whereas the tables of Bourne`s "Almanacke for three yeares" (London 1571) and "Regiment for the Sea" give a maximum declination of 23 degrees and 28 minutes. It should be fun to compare the values of the different tables to develop some kind of lineage; I have done this for the oldest German navigation manual of 1578 and found out that they are derived from the Portuguese "Tractado da spera" of ca. 1516. Best regards, Wolfgang Koeberer Life member of TINSTAARG (There is no such thing as a responsible gun) TOTTCHAIAUITPOBIAGW (The only thing that Charlton Heston and I agree upon is that Patrick O`Brian is a great writer) CSSTHOBIEMAATNCTKA (Can`t somebody stop this habit of broadcasting in e-mails memberships and allegiances that nobody cares to know about)