Comparative Navigational Practices

The importance of the stars in navigation is attested in all seafaring cultures. The use of the rising or setting points of stars as horizon markers seems to be universal in all such groups where we have adequate data. This involved a de facto recognition of latitude, not necessarily formally conceptualized. The ecliptic as the path of the Sun, and the broader surrounding path of the Moon and planets, both seem to have been recognized widely and probably universally by seafarers. The limits of the path of the Sun at the Tropics of Cancer and Capricorn usually seem to have been formalized. Evidence of a conceptualization of the equator is also widespread. The conception of longitude was formally recognized in all areas influenced either by China or by the Hellenistic culture. Techniques of determining the actual longitude of a particular place, whether on land or sea, were limited to direct measures of distance on land or very rough estimates of distance traveled on the sea and to the technique of simultaneous observation of lunar eclipses from different places. Pingree thinks that this technique is the only one that could have been used to get the difference in longitude of Alexandria and Ujjain with the precision with which it is given in the Panchasiddhantika (see §9.1.3). Islamic mariners made extensive use of this technique in creating maps, but some of the errors are larger than would be expected. See §4.1.1.2 for the relationship between longitude and time, and Harley and Woodward (1994) for a fuller discussion of problems in determining longitude.

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