9) Venus Calendar

Calendar on Venus

Reference courtesy --- 


  The orbit of Venus is nearly a perfect circle, and the planet has no axial tilt, so it has no seasons. Any point along the orbit is essentially indistinguishable from any other one, and return to it has no special meaning. Thus, there is no solar calendar on Venus. Instead, from the very beginning of the human settlement, the universally accepted calendar on Venus has been a geo calendar, based on the motion of Venus relative to Earth. The period of 584 days between the closest approaches (the inferior conjunctions) is termed a vear. Five vears are almost equal to eight Earth years.

            It takes 13/5 of a turn around the Sun for Venus to arrive at the next conjunction, and 8/5 of an Earth year for Earth to do the same. Hence, there was a debate about which calendar to adopt, a 13-month calendar or a 16-month calendar. In the 13-month calendar, one month is equal to the average amount of time it takes Venus to pass from one point of its pentagon to the next one along the orbit: approximately, 45 days. The thirteen months are named after the Mayan zodiac constellations: Balam, Coz, Batz, Xibkay, Kutz, Mo’an, Keh, Dzec, Zotz, Aak, Tzub, Kan, Pek. They have 45 days each, except for the first one (Balam), which has 44 days.

Due to the difference between the 584-day calendar and the synodic period of Venus (583.92 days), one day must be subtracted every 12.5 vears. This was done as follows: one day was subtracted from the middle month (Keh) every 13th, 38th, 63rd vear, etc. (in periods of 25), and one day was subtracted from the last month (Pek) every 25th, 50th, 75th vear, etc. But this calendar didn’t gain wide usage.

            The 16-month calendar, which eventually won, is based on the average amount of time it takes Earth to travel from one point of its conjunctions pentagon to the next one. This way, the middle of the vear corresponds to the superior conjunction, when Earth faces Venus across the Sun. Each 73-day period is divided into two months. The intercalation is similar to the 13-day calendar: one day is subtracted from the 8th month every 13th, 38th, 63rd vear, etc. and one day is subtracted from the last month every 25th, 50th, 75th vear, etc. The first vear began 12 hours earlier than the true time, so that the deviation from the true time does not normally exceed 12 hours in either direction. 

Long count ---



 Long Count

Main article: Mesoamerican Long Count calendar

Since Calendar Round dates repeat every 18,980 days, approximately 52 solar years, the cycle repeats roughly once each lifetime, so a more refined method of dating was needed if history was to be recorded accurately. To specify dates over periods longer than 52 years, Mesoamericans used the Long Count calendar.

The Maya name for a day was k'in. Twenty of these k'ins are known as a winalor uinal. Eighteen winals make one tun. Twenty tuns are known as a k'atun. Twenty k'atuns make ab'ak'tun.

The Long Count calendar identifies a date by counting the number of days from the Mayan creation date 4 Ahaw, 8 Kumk'u (August 11, 3114 BC in the proleptic Gregorian calendar or September 6 in the Julian calendar). But instead of using a base-10 (decimal) scheme like Western numbering, the Long Count days were tallied in a modified base-20 scheme. Thus is equal to 25, and is equal to 40. As the Uinal unit resets after only counting to 18, the Long Count consistently uses base-20 only if the tun is considered the primary unit of measurement, not the k'in; with the k'in and Uinal units being the number of days in the tun. The Long Count represents 360 days, rather than the 400 in a purely base-20 (vigesimal) count.

 Diagram courtesy---