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Uma forma pioneira portuguesa de navegar pela altura do Sol
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Orientador(es)
Resumo(s)
Esta dissertação de mestrado estuda as tábuas solares dos chamados Almanaques
Portugueses de Madrid (Ms 3.349), preservados na Secção de Manuscritos da
Biblioteca Nacional de Espanha.
Formula-se a hipótese de que as informações ali registadas, em dois enunciados
distintos de “tavoas da altura do Sol”, podiam ser utilizadas para determinar grosso
modo uma posição em latitude, numa forma primeva de navegação astronómica em
alto-mar.
Essa determinação da posição seria possível sem fazer qualquer operação matemática
complexa, e necessitando apenas de alguns conhecimentos astronómicos
básicos: bastaria dispor de uma daquelas tabelas, saber o dia do ano, utilizar o
quadrante - o mais simples dos instrumentos de navegação astronómica - e fazer
uma conta de somar ou subtrair.
Faz-se a demonstração teórica da viabilidade desta forma de navegação em altomar,
fora da vista de terra. A precisão das mencionadas tabelas é analisada por
confronto com os resultados de um programa de simulação astronómica e avaliada
por métodos estatísticos.
Também se comprova que tais tabelas da altura do Sol não têm precedentes nos
guias náuticos anteriores, de origem árabe, mediterrânica, hebraica ou ibérica, e que
as mesmas não têm qualquer outra utilidade astrológica ou astronómica conhecida,
a não ser para a navegação marítima.
Uma vez que o referido códice, Almanaques Portugueses de Madrid, já foi datado
por Luís de Albuquerque como tendo sido escrito provavelmente entre 1321 e 1339,
fica assim demonstrado que o conhecimento português de navegação astronómica
em alto-mar era muito anterior (possivelmente até em mais de um século), ao que
atualmente se dá como cientificamente comprovado (c. 1460).
Analisam-se ainda as instruções náuticas, precisas e fáceis de aplicar, para encontrar
uma distância em relação a Lisboa, à Madeira, ou a qualquer outro local para
o qual existissem tábuas da altura do Sol, tal como foram posteriormente impressas
no Reportório dos tempos, de Valentim Fernandes.
Actualmente só se conhece uma única primeira edição incompleta do Reportório.
Data de 1518. Foram, no entanto, depois impressas várias reedições daquela obra,
utilizando matrizes tipográficas anteriores. O livro completo mais antigo que hoje se conhece, uma edição de 1552, retém as instruções para se quiserdes saber quanto
contra ho navio polla altura do Sol.
Conclui-se - embora apenas indiretamente se comprove - que a navegação astronómica
pelo Sol, depois desenvolvida e utilizada de forma pioneira pelos navegadores
portugueses no Atlântico para a torna-viagem, (a volta do mar largo ou volta do mar
da Baga), estava em uso muito antes do que é atualmente dado como conhecimento
adquirido.
Tal navegação pioneira pelo Sol já havia sido sugerida por vários historiadores,
como Jaime Cortesão, António Barbosa, Gago Coutinho, Fontoura da Costa, Eva
Rimington Taylor ou Avelino Teixeira da Mota.
Teria sido pois uma simples, mas eficaz, navegação por alturas, que na aurora
dos Descobrimentos precedeu em muitas décadas uma determinação mais exata da
latitude pela declinação do Sol.
This thesis intends to study the solar tables of the so-called Portuguese Almanacs of Madrid – the codex Ms. 3.349, preserved in the Manuscripts Section of the National Library of Spain. The hypothesis presented is that the information recorded there, specifically in two distinct tables of the height of the Sun, could be used to roughly determine a position in latitude in relation to Lisbon, in a primeval form of astronomical navigation on the high seas. Thus without any complex mathematical operation, requiring only some basic astronomical knowledge: it would suffice to have one of those tables, to know the day of the year, to use the quadrant, the simplest of the astronomical instruments, and to do just one addition or subtraction. A theoretical demonstration of the feasibility of this earlier form of high seas navigation is made. The accuracy of the aforementioned tables is analyzed by comparison with the results produced by an astronomical simulation software and a statistical evaluation made. It is also established that such tables of Sun height are unprecedented in known earlier nautical guides of Arab, Mediterranean, Hebrew or Iberian origin, and that those tables have no other known astrological or astronomical utility. Since that codex was already dated by Luís de Albuquerque as having been written most likely between 1321 and 1339, it is thus proposed that the Portuguese knowledge of astronomical navigation on the high seas was much earlier (possibly more than a century), to what is presently accepted as scientifically proven (c.1460). The thesis also analyses the precise, step by step and easy-to-apply nautical instructions to find a distance in range from Lisbon, Madeira, or any other location by the Sun‘s height tables were afterwards also printed in the Repertory of the times, by Valentim Fernandes. At the present day, only a single incomplete first edition of the Repertory is known. It was printed in 1518. However, they remain several reprints, which used older typographical plates, and the earlier complete book known, the 1552 edition, retains the instructions on how to proceed “if you wish to know how the ship counts by the height of the Sun”. This thesis concludes - albeit only indirectly proves – that astronomical navigation by the Sun, later on used pioneerely by the Portuguese navigators in the Atlantic for the return voyages, were in use long before what is at present accepted as acquired knowledge. A pioneer navigation by the Sun meridien height had already been suggested by several historians, such as Jaime Cortesão, António Barbosa, Gago Coutinho, Fontoura da Costa, Eva Rimington Taylor or Avelino Teixeira da Mota. It would have been a simple navigation by heights, which in the dawn of the age of the Discoveries preceded in many decades a more accurate determination of latitude by the declination of the Sun.
This thesis intends to study the solar tables of the so-called Portuguese Almanacs of Madrid – the codex Ms. 3.349, preserved in the Manuscripts Section of the National Library of Spain. The hypothesis presented is that the information recorded there, specifically in two distinct tables of the height of the Sun, could be used to roughly determine a position in latitude in relation to Lisbon, in a primeval form of astronomical navigation on the high seas. Thus without any complex mathematical operation, requiring only some basic astronomical knowledge: it would suffice to have one of those tables, to know the day of the year, to use the quadrant, the simplest of the astronomical instruments, and to do just one addition or subtraction. A theoretical demonstration of the feasibility of this earlier form of high seas navigation is made. The accuracy of the aforementioned tables is analyzed by comparison with the results produced by an astronomical simulation software and a statistical evaluation made. It is also established that such tables of Sun height are unprecedented in known earlier nautical guides of Arab, Mediterranean, Hebrew or Iberian origin, and that those tables have no other known astrological or astronomical utility. Since that codex was already dated by Luís de Albuquerque as having been written most likely between 1321 and 1339, it is thus proposed that the Portuguese knowledge of astronomical navigation on the high seas was much earlier (possibly more than a century), to what is presently accepted as scientifically proven (c.1460). The thesis also analyses the precise, step by step and easy-to-apply nautical instructions to find a distance in range from Lisbon, Madeira, or any other location by the Sun‘s height tables were afterwards also printed in the Repertory of the times, by Valentim Fernandes. At the present day, only a single incomplete first edition of the Repertory is known. It was printed in 1518. However, they remain several reprints, which used older typographical plates, and the earlier complete book known, the 1552 edition, retains the instructions on how to proceed “if you wish to know how the ship counts by the height of the Sun”. This thesis concludes - albeit only indirectly proves – that astronomical navigation by the Sun, later on used pioneerely by the Portuguese navigators in the Atlantic for the return voyages, were in use long before what is at present accepted as acquired knowledge. A pioneer navigation by the Sun meridien height had already been suggested by several historians, such as Jaime Cortesão, António Barbosa, Gago Coutinho, Fontoura da Costa, Eva Rimington Taylor or Avelino Teixeira da Mota. It would have been a simple navigation by heights, which in the dawn of the age of the Discoveries preceded in many decades a more accurate determination of latitude by the declination of the Sun.
Descrição
Palavras-chave
Biblioteca Nacional (Espanha) - Manuscrito. Ms. 3349 Almanaques portugueses - Madrid (Espanha) Navegação - Idade Média - História Astronomia medieval - Portugal - História Navegação astronómica - Idade Média - História Astronáutica na navegação - Idade Média - História Arte e ciências navais - Idade Média - História História naval - Idade Média - História Teses de mestrado - 2020