Mayan Calendar

42 The solar zeniTh tubes and alignments The dates for sowing and harvesting were, and still are, fixed by the Maya at the two annual zenith passage days of the sun, when the sun is directly overhead, when a gnomon casts no shadow at noon. At some Mesoamerican sites, such as Xochicalco and Monte Alban, there are buildings in which a zenith tube projects a vertical sunbeam onto the floor at midday below. In the Yucatan, bottleshaped underground chambers called chultunes may have served the same purpose. There are two seasonsrainy and dry, starting in AprilMay and November. The onset of the rainy season coincides with the first zenith passage in May for much of the Maya area, and maize corn is planted shortly after. At the second solar passage a second maize crop is planted. At higher altitudes, maize and beans are planted in March and harvested 260 days later in December. The solar nadir dates when the sun passes directly underfoot are spaced six months from the zenith passage dates and the November solar nadir coincides with the beginning of the dry season. Zenith tubes may also have been used to observe the zenith passage of important constellations. There is evidence suggesting the Aztecs interpreted the conjunction of the Pleiades with the zenith sun as a signal for the end of one era and the start of the next. midsumme r sunrise Pollux r ising Castor r ising C a n o p us r is i ng Ac her na r set tin g Fomalha ut settin g Venus sou thernmos t setting midwinter sunset equinox sunset zeni th p assa ge s unse t Ven us nor the rn mos t se tting Chichen Itza, Mexico Alignments from the Caracol Observatory Built 600850 ad, remodeled 8001200 ad after Aveni , Gibbs Hartung The solar year, equinoxes, and solstices were determined by alignments, as here at Chichen Itza. The Central Mexican yearsign may represent an instrument that projects a cross on the zenith passage days after Jenkins. Sun directly overhead shines down a vertical zenith tube at Monte Alban after Hartung.