11/21/2022 0 Comments Horizon zero dawn map meridian city![]() ![]() The method is described in the Sûrya Siddhânta, a Sanskrit treatise on Indian astronomy thought to date from the late 4th century or early 5th century CE. Īncient Hindu astronomers were aware of the method of determining longitude from lunar eclipses, assuming a spherical earth. Given the difficulties of astronomical measures of longitude in classical times, most if not all of Ptolemy's values would have been obtained from distance measures and converted to longitude using the 500 value. Luccio (2013) has analysed these discrepancies, and concludes that much of the error arises from Ptolemy's underestimate of the size of the earth, compared with the more accurate estimate of Eratosthenes – the equivalent of 500 stadia to the degree rather than 700. Thus from Ptolemy's tables, the difference in Longitude between Gibraltar and Sidon is 59° 40' 0', compared to the modern value of 40° 23'0', about 48% too high. : 551–553 Apart from the difficulties in estimating rectilinear distances and directions, the most important of these is a systematic over-estimation of differences in longitude. While Ptolemy's system is well-founded, the actual data used are of very variable quality, leading to many inaccuracies and distortions. No maps (or manuscripts of his work) exist that are older than the 13th century, but in his Geography he gave detailed instructions and latitude and longitude coordinates for hundreds of locations that are sufficient to re-create the maps. : 543 : 90 For large area this leads to unacceptable distortion, and for his map of the inhabited world, Ptolemy used projections (to use the modern term) with curved parallels that reduced the distortion. Until then, all maps had used a rectangular grid with latitude and longitude as straight lines intersecting at right angles. Ptolemy, in the 2nd century CE, based his mapping system on estimated distances and directions reported by travellers. Ptolemy's map of the Mediterranean superimposed on a modern map, with Greenwich as the reference longitude But the method is sound, and this is the first recognition that longitude can be determined by accurate knowledge of time. : 11 This method was not very accurate, given the limitations of the available clocks, and it was seldom done – possibly only once, using the Arbela eclipse of 330 BCE. He also proposed a method of determining longitude by comparing the local time of a lunar eclipse at two different places, to obtain the difference in longitude between them. ![]() : 31 So longitudes could be expressed as degrees east or west of the primary meridian, as we do today (though the primary meridian is different). ![]() By the 2nd century BCE Hipparchus was using a systematic coordinate system, based on dividing the circle into 360°, to uniquely specify places on Earth. His prime meridian (line of longitude) passed through Alexandria and Rhodes, while his parallels (lines of latitude) were not regularly spaced, but passed through known locations, often at the expense of being straight lines. Eratosthenes in the 3rd century BCE first proposed a system of latitude and longitude for a map of the world. ![]()
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