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Authors
Abstract(s)
Nos séculos passados, a única forma de se calcular a posição do navio era
através dos astros. Ao longo dos tempos, foram vários os autores que tentaram
desenvolver os métodos de cálculo do ponto astronómico. O Sol era o astro mais
utilizado, porque permitia o cálculo da latitude pela passagem meridiana. Entretanto, face às limitações desse processo, foram criados métodos de cálculo dessa
coordenada por extrameridianas. No final do século xviii e ao longo do século xix,
calculava-se a longitude pelo ângulo horário, graças ao aparecimento do cronómetro,
e a latitude pela passagem meridiana, em momentos diferentes do dia.
Posto isto, o trabalho que se segue apresenta um estudo do desenvolvimento
histórico dos métodos de cálculo da latitude por extrameridianas do Sol e expõe
matematicamente dois desses processos, o de Cornelis Douwes e o de James Ivory,
simplificado por Edward Riddle. De seguida, aplica-os a dados de observações reais,
em simultâneo com o cálculo da longitude pelo ângulo horário, já que não foram
encontrados registos de nenhuma experiência semelhante. Com o objetivo de avaliar
a fiabilidade desses métodos e procurar justificações para a falta de registos da sua
aplicabilidade, os resultados são comparados com posições GPS (Global Positioning
System), registadas no momento das observações. Finalmente, aponta os motivos
que poderão ter levado os pilotos dos séculos xviii e xix a rejeitar os métodos de
cálculo da latitude por extrameridianas — tendo em conta a quantidade de literatura que os expunha — continuando a preferir o cálculo da latitude pela passagem
meridiana, quando possível, e o da longitude num instante diferente, cientes do erro
que o resultado pudesse trazer.
In past centuries, the only way to calculate the ship’s position was through the stars. Over time, several authors have tried to develop methods to calculate the astronomical point. The sun was the most used star, because it allowed the calculation of latitude by meridian passage. However, given the limitations of this process, methods of calculating this coordinate by extrameridians were created. At the end of the 18th century and throughout the 19th century, the longitude was calculated by the hour angle, thanks to the appearance of the chronometer, and the latitude by the meridian passage, obtained at different times of the day. Having said this, the following paper presents a study of the historical development of the methods of calculating latitude by extrameridians of the Sun and mathematically exposes two of these processes, that of Cornelis Douwes and James Ivory, simplified by Edward Riddle. Then, applies them to data from real observations, simultaneously with the calculation of longitude by the hour angle, since no records of any similar experiment were found. In order to evaluate the reliability of these methods and seek justifications for the lack of records of their applicability, the results are compared with GPS (Global Positioning System) positions recorded at the time of observations. Finally, it points out the reasons that may have led 18th and 19th century pilots to reject the methods of calculating latitude by extrameridian — taking into account the amount of literature that exposed them — continuing to prefer the calculation of latitude by meridian passage, when possible, and that of longitude at a different instant, aware of the error that the result could bring.
In past centuries, the only way to calculate the ship’s position was through the stars. Over time, several authors have tried to develop methods to calculate the astronomical point. The sun was the most used star, because it allowed the calculation of latitude by meridian passage. However, given the limitations of this process, methods of calculating this coordinate by extrameridians were created. At the end of the 18th century and throughout the 19th century, the longitude was calculated by the hour angle, thanks to the appearance of the chronometer, and the latitude by the meridian passage, obtained at different times of the day. Having said this, the following paper presents a study of the historical development of the methods of calculating latitude by extrameridians of the Sun and mathematically exposes two of these processes, that of Cornelis Douwes and James Ivory, simplified by Edward Riddle. Then, applies them to data from real observations, simultaneously with the calculation of longitude by the hour angle, since no records of any similar experiment were found. In order to evaluate the reliability of these methods and seek justifications for the lack of records of their applicability, the results are compared with GPS (Global Positioning System) positions recorded at the time of observations. Finally, it points out the reasons that may have led 18th and 19th century pilots to reject the methods of calculating latitude by extrameridian — taking into account the amount of literature that exposed them — continuing to prefer the calculation of latitude by meridian passage, when possible, and that of longitude at a different instant, aware of the error that the result could bring.
Description
Keywords
Latitude por Extrameridianas Cornelis Douwes James Ivory Edward Riddle Longitude pelo Ângulo Horário