<P> The Vague Year of 365 days is similar to our modern calendar, consisting of 18 months of 20 days each, with an unlucky five - day period at the end . The Vague Year had to do primarily with the seasons and agriculture, and was based on the solar cycle . The 18 Maya months are known, in order, as: Pop, Uo, Zip, Zotz, Tzec, Xuc, Yaxkin, Mol, Chen, Yax, Zac, Ceh, Mac, Kankin, Maun, Pax, Kayab and Cumku . The unlucky five - day period was known as Uayeb, and was considered a time which could hold danger, death and bad luck . </P> <P> The Vague Year began with the month of Pop . The Maya 20 - day month always begins with the seating of the month, followed by days numbered 1 to 19, then the seating of the following month, and so on . This ties in with the Maya notion that each month influences the next . The Maya new year would start with 1 Pop, followed by 2 Pop, all the way through to 19 Pop, followed by the seating of the month of Uo, written as 0 Uo, then 1 Uo, 2 Uo and so on . These two cycles coincided every 52 years . The 52 - year period of time was called a "bundle" and was similar to a modern - day century . </P> <P> While the Gregorian calendar is now in worldwide use for secular purposes, various medieval or ancient calendars remain in regional use for religious or social purposes, including the Julian calendar, the Hebrew calendar, the Islamic calendar, various Hindu calendars, the Zoroastrian calendar etc . </P> <P> There are also various modern calendars that see limited use, either created for the use of new religious movements or reformed versions of older religious calendars, or calendars introduced by regionalist or nationalist movements . </P>

Who invented the calendar system we use today