The xochicalco solar zenith tube (10 pts). xochicalco is an ancient city in central mexico at latitude 19 degrees n, and was populated by 20,000 or more people in the years 700-900 ad. a vertical shaft in the ground lead to an underground chamber, and on certain dates the sun shines directly down the "zenith tube. a) on how many days each year will this happen? what is the declination of the sun on these days? explain your reasoning. b) use the rectangular star charts at the end of the starbookto estimate on which dates the sun will shine directly down the tube. explain your answer center of the two charts is the celestial equator note: for question 2b, the straight line across the above ond below are the declination grid lines. note that the two charts end-to-end cover the full sky between +50 and -60 declination. the round charts cover the celestial poles (not needed here). the curved line above and below the equator is the ecliptic and it is marked with the dates of the sun's position. you may wish to print out the chart and use a ruler to estimate the zenith dates