Julian Calendar:
- Until 45 BCE, the Roman calendar was 12 months and spanned 355 days, with the occasional addition of a ‘mensis intercalaris’, an extra 27 or 28 day month between February and March
- Julius Caesar sought to change this as the politicians responsible for deciding if there would be an extra month could abuse the power they had to lengthen a magistrate’s term in office
- With knowledge from his recent time spent in Egypt and the help of Greek mathematician and astronomer, Sosigenes of Alexandria, the Julian calendar was created
- Lunar months were tweaked to closer fit a 365.25 day orbit of the Sun, with leap years successfully incorporated every 4 years, meaning no human intervention was needed
- Julian calendar remained in place until Pope Gregory XIII made minor adjustments in 1582 CE that stated centenary years wouldn’t be observed as leap years unless they were divisible by 400
- This change corrects the 3.1 days the Julian calendar gains every 400 years and gave us the Gregorian calendar
Egyptian Solar Calendar:
- Having measured the length of a solar year accurately to within 11 minutes and 14 seconds of the true value by 300 BC, the Decree of Canopus unsuccessfully attempted to integrate the use of leap years in 238 BCE
- The Egyptian calendar was adopted in around 3000 BCE and like many others, its main purpose was to accurately predict an important natural event
- For the Egyptians, the new year began in what is now July, marked by the helical rising of Sirius, the Dog Star
- Using the star’s reappearance at sunrise as a fixed point for the solar year to begin, they could accurately predict the annual flooding of the Nile River
- The surge of water flooded the desert valley and replenished the soil with much needed nutrients imperative for successful farming
Thai Buddhist Calendar:
- The Thai solar calendar, similar to the Gregorian calendar, has been used for legal and commercial reasons since 1888 CE and allowed them to fix the date of the traditional Thai new year’s celebration in April, which drifted under previous calendars due to irregularity between the Moon’s cycle and the Sun’s
- However, years in Thailand are still widely measured in BE (Buddhist Era), not a calendar as such but a year numbering system beginning when Buddha attained nirvana
- For the Thai calendar, this was set at 543 BCE, putting Thailand 543 years ahead of Western civilisations
Celtic Moon Calendars:
- Celts split their year into a dark half and a light half – the year began at the dark half with Samhain at the late October full moon, and the light half began at Beltane in early May
- Followed a lunar calendar but noticed months would drift into other seasons
- The Coligny calendar is an inscribed bronze plaque which demonstrates that, by the 2nd century CE, they had established a five year cycle with an intercalary month inserted every 2.5 years to course correct based on the Metonic Cycle
- This is a larger lunar cycle originally discovered by the Babylonians in around 500 BCE, whose name comes from Meton of Athens who rediscovered it in the 5th century BCE
- It spans 235 lunar cycles, (approximately 19 years) at which point the Moon’s phases begin to recur on the same days
Prehistoric Calendars:
- Built in around 2000 BCE, Stonehenge is perhaps one of the most visually impressive early calendars ever found which takes into account the path of the Sun, Moon, and also specific constellations of stars
- Using concentric circles of holes, pillars and archways it marks solstices and equinoxes with the help of the sunrise
- Predating Stonehenge by 6,000 years and the Mesopotamian calendars by nearly 5,000 years, the Warren Field Mesolithic Calendar is the earliest calendar found so far
- Discovered in Aberdeenshire on 2004, the calendar is made up of 12 pits representing lunar months which align with a prominent nearby topographic point at sunrise on the winter solstice to act as a fixed point
