The Venus calendar seems to have taken form in the sixth century B. C. on the basis of heliacal risings of the planet as morning star in sets of five making an eight year cycle. The dates in the Mayan calendar especially emphasized in connection with Venus are 19 Xul, 18 Kayab, 12 Yax, 6 Zip, and 5 Kankin standing exactly 584 days apart, while the corresponding dates in the Gregorian calendar are April 12, November 17, June 24, January 29, and September 5. When these sets of dates, one in a fixed and the other in a vague calendar are carried back to a common focus they are found to correspond very closely with the proper astronomical phase of Venus. The maximum difference of the true positions of Venus from the positions in the Venus calendar is then only two days, plus or minus.
The coincidences of the 8 day period of obscuration of Venus at inferior conjunction with the following round numbers in the day count was memorialized by important monuments:—
| 9.14.0.0.0, | 6 Ahau 13 Muan, | Feb. 4, 452 A. D. | Venus rises as morning star |
| 9.17.0.0.0, | 13 Ahau 18 Cumhu, | Mar. 27, 511 A. D. | Venus invisible during conjunction |
| 10.0.0.0.0, | 7 Ahau 18 Zip, | May 17, 570 A. D. | Venus invisible during conjunction |
| 10.3.0.0.0, | 1 Ahau 3 Yaxkin, | July 6, 629 A. D. | Venus about to set as evening star |
The Venus table in the Dresden Codex, the introductory page of which has been explained in an earlier section (see [Plate XXIV]) emphasizes the same Mayan and Gregorian positions of Venus as the ancient monuments but this table was evidently intended to be used between the Tenth and Thirteenth centuries A. D. The point of departure for the table is 9.9.9.16.0, 1 Ahau 18 Kayab, April 12, 363 A. D., which does not coincide with an heliacal rising of the planet, although April 12 and 18 Kayab occur in other connections at the time of the inauguration of the Venus calendar in the Sixth century B. C. But in the Lunar table we find 10.19.6.1.0, 4 Ahau 18 Kayab, November 20, 950, which does reach an heliacal rising of Venus as morning star.
Summary of Mayan History.
A brief summary of Mayan history is given below:—
Protohistoric Period
613 B. C. to 176 A. D. 7.0.0.0.0 to 9.0.0.0.0
The counting of days apparently began on August 6, 613 B. C. and the civil calendar in perfected form was inaugurated about 580 B. C. when 0 Pop coincided with the winter solstice, while the Venus calendar emerged half a century later. The calendarial inventions, the numerical notation and the hieroglyphic system may, perhaps, be credited to the genius of one man afterwards deified as Itzamna. The earliest contemporary Mayan date occurs on a jade statuette from San Andres Tuxtla, and is May 16, 98 B. C. The next earliest one is on the jade tablet known as the Leyden Plate and is November 17, 60 A. D., having reference to the Venus calendar. This is followed almost immediately by several contemporary dates on monuments at Uaxactun which also are of astronomical import. The design on the Leyden Plate shows that the characteristic details of Mayan drawing had already been developed and we may surmise that during the protohistoric period the early carvings were on wood instead of stone and that the peculiar religion of the Mayas was even then beginning to crystallize around the serpent, the jaguar, etc.