A Method of Measuring Shadow of the Sun by 10 Poles

It is described in the Yi language literature《Astronomy in the Yi nationality of Yunnan》that the establishment of 10—month solar calendar was based on astronomical ob-servations. One method was setting up 10 poles to datermine length of the year, solstices and equanoxes by measuring shadow of the sun and the Big Dipper. The relative positions of 10 poles and practical observation are discussed in the paper. The necessary conditions for 3 ob-serving points are calculated quantitatively with modern observational data.