529: Calendar by David Ewing Duncan
529.3: Duncan, David Ewing. Calendar: Humanity’s Epic Struggle to Determine a True and Accurate Year. New York: Avon, 1998. 241 pp. ISBN 0-380-97528-9.
529 is a curious section in the DDC. 520s are astronomy, but the last section in the division–529–is classed as chronology. This is because for many millennia, cultures have counted their days and nights by the sun and the stars. Long before electric wristwatches and atomic clocks, the hours of the day were tolled out by bell towers and sun sightings.
While Gould’s book (here) was superficial and condescending, David E. Duncan’s Calendar is vast and learned. You can tell just from the first chapter that the author consulted as many sources as is possible for this book. His goal is to track the evolution of the modern 12-month, 365-day (or 366) from its earliest form to the present. Along the way, he weaves a thread through Cro-Magnon bone carvers, Egyptian pharoahs, Indian mathematicians, and Catholic philosophers.
There are far too many details to go through here, but here are my favorite two parts:
1) The names of the 12 months on our calendar have changed very little since the times of Romulus and Julius Caesar. The original calendar, created in the eighth century BCE, started in March, and only had ten months: Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, and December. In 700 BCE, King Numa tacked Januarius and Februarius to the end to bring it to twelve. Julius Caesar changed Quintilis to Julius (because he could); Augustus Caesar, the next emperor, changed Sextilis to Augustus. And now we have the modern month cycle. Luckily the Caesars decided that conquering two months was enough.
2) In order to perfectly calculate the length of a calendar year in relation to the sun and the moon, you need the number zero. Without zero, people had been doing mathematical calculations using Roman numerals or cuneiform combined with fractional components (for instance 24.96 would be written as XXII + 1/2 + 1/4 + 1/20 + 1/100). When the zero was conceptualized and use in math sometime in India in the seventh century CE, only then astronomers could further pinpoint the exact length of a year (which is currently reckoned at 365.242199 days).
All in all, it was a very interesting and detail-packed treatise on how cultures have interacted with time and astronomy.