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Analysis of the Astronomical Information in Tachard: “Voyage to Siam in the Year 1685”
... You Gislén, (2004), Gislén et al. (2018) and Orchiston (2016) have all written about this Thai eclipse, only Cassini mentioned Promontorium Somnii. ...
... Also the method of measuring lunar distances (de Grijs, 2020) from reference stars could be used but there is no indication the this method was ever used by the French Jesuits in China. The French Jesuit Guy Tachard (1651Tachard ( -1712, determined the longitude of Cape Town timing the eclipse of the Jovian moon Io in the night of 2 June 1685 and of Lop Buri in Siam (present-day Thailand) using the lunar eclipse of 11 December 1685 (see Gislén, 2004;Gislén et al., 2018;Orchiston et al., 2016;Tachard, 1981). An even rarer event of this kind is documented in the records, the transit of Mercury on 10 October 1689, which was observed and timed from Canton, China, by Father Jean de Fonteney (1643-1710 at about 3 o'clock in the afternoon (Anonymous, 1729: 825). ...
... Other papers in the series attempt to provide an overview (Orchiston, 2021b), or discuss solar and lunar eclipses visible from Lop Buri and Ayutthaya between 1681 and 1688 (Orchiston et al., 2019;c.f. Smithies, 2003), but especially the lunar eclipses of 22 February 1681 (Orchiston et al., 2021a) and 11 December 1685 (Gislén et al., 2018;Orchiston et al., 2016; c.f. Gislén, 2004). After providing suitable background material, this paper focusses on the solar eclipse of 30 April 1688, which was visible as a partial event from Siam. 1 But before examining this particular eclipse we need to meet King Narai, who made possible the introduction of scientific astronomy in Siam at this time. ...
... A lunar eclipse looks the same for all observers on the Earth where the Moon is above the horizon and the eclipse events are simultaneous for all observers and can because of this fact be used to determine geographical longitude differences between locations. It was an important tool for the French Jesuits who visited Siam in CE 1685 when they determined the longitude of Lopburi using the lunar eclipse of 11 December 1685 (Gislén, 2004;Gislén et al., 2018). Figure 6 shows the situation at the time of a geocentric conjunction between the Sun and the Moon. ...
Many of the calendrical records in Southeast Asia contain information on the longitudes of the Sun, the Moon and the planets – something that is valuable for the dating of these records. Both the Burmese and the THai use calculations schemes for these longitudes that are almost identical to the original Suryasiddhanta schemes.After the change to the Thandeikta calendar the Burmese changes some of the paramaters involved, in general following those of the modern Suryasiddhanta.
... But first, they need a reliable time source, just as the Jesuit astronomers did back in 1685. Gislén (2004) has already reviewed the clocks that the Jesuits had in Lop Buri. There was a ‗Great pendulum' and a ‗Little pendulum', and ...
On 18 February 1679 Paris Observatory astronomer Jean Dominique Cassini presented a new map of the Moon to the Academy of Sciences in Paris, and this then became the standard reference work for French astronomers who carried out selenographical observations. Among these was a contingent of Jesuit missionary-astronomers who sailed from Brest on 3 March 1685, bound for China. En route they were forced to spend some months in Siam (present-day Thailand) and used the map when they observed the lunar eclipse of 11 December 1685. In this paper we examine the creation of the 1679 Moon map and its use by the French Jesuit missionary-astronomers in Siam in 1685.
... But first, they need a reliable time source, just as the Jesuit astronomers did back in 1685. Gislén (2004) has already reviewed the clocks that the Jesuits had in Lop Buri. There was a ‗Great pendulum' and a ‗Little pendulum', and ...
On 18 February 1679 Paris Observatory astronomer Jean Dominique Cassini presented a new map of the Moon to the Academy of Sciences in Paris, and this then became the standard reference work for French astronomers who carried out selenographical observations. Among these was a contingent of Jesuit missionary-astronomers who sailed from Brest on 3 March 1685, bound for China. En route they were forced to spend some months in Siam (present-day Thailand) and used the map when they observed the lunar eclipse of 11 December 1685. In this paper we examine the creation of the 1679 Moon map and its use by the French Jesuit missionary-astronomers in Siam in 1685.
The methods and quality of seventeenth century timings of immersions and emersions of the Galilean satellite Io were studied. It was found that the quality of the observations was very good but that in the cases where these observations were used for longitude determinations, the results were impaired by the inaccuracy of Cassini's ephemerides that were used.
L'auteur explique les methodes de calcul et de predictions des eclipses utilisees en Asie du Sud-Est et demontre le degre de precision de ces calculs ainsi que l'interaction entre astronomie et astrologie existant a l'epoque et motivant la recherche de ces donnees.
The Earth, in its diurnal rotation, acts as a remarkably accurate timekeeper. However, small variations in the length of the day occur at the millisecond level. Historical eclipse observations, recorded by various ancient and medieval cultures, enable changes in the Earth's spin rate to be monitored with fair precision as far back as around 700 BC. Although lunar and solar tides are the main causes of long-term changes in the length of the day, the early observations reveal that non-tidal mechanisms are also important. In this paper I review both the historical development of this subject and recent advances.
A relation of the Voyage to Siam
- Guy Tachard
Guy Tachard, ''A relation of the Voyage to Siam'', White Orchid Press, Bangkok 1981. ISBN 974-89393-6-4. Also relevant parts of the French original have been consulted.
Historical Eclipses and Earth's Rotation'', Cambridge Univer-sity Press
- F Richard
- Stephenson
F. Richard Stephenson, ''Historical Eclipses and Earth's Rotation'', Cambridge Univer-sity Press, 1997, ISBN 0-521-46194-4.
Annales cé du dix-septième siècle'' (reprint Paris
- A.-G Pingré
A.-G. Pingré, ''Annales cé du dix-septième siècle'' (reprint Paris 1901, ed. M. G. Bigourdan).
http://www.moshier.net/ 5. Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac. London, Her Majesty's Stationery Office
- Computamaps Hyland
- Cape Town
- South Africa
Generously provided by Justin Hyland, ComputaMaps, Cape Town, South Africa.
4. http://www.moshier.net/
5. Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac. London, Her Majesty's Stationery Office, 1961. ISBN 0-
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