Andy sends a tine gift book to Nathan Lawson, age 14, of White Plains, N.Y., for his question:
WHEN WAS THE FIRST CALENDAR USED?
A calendar is a system of measuring time, by dividing tame into days, weeks, months and years. Calendars go back to ancient times. The early Babylonians had one thousands of years ago that was based on 12 lunar months of 30 days each.
The variations among the many calendars in use from ancient to modern times have been caused by the inaccuracy of the earliest determinations of the year, together with the fact that a year cannot be divides evenly.
The earliest calendars based on lunar months failed to agree with the seasons. The ancient Babylonians added extra months when necessary to keep the calendar in line.
The ancient Egyptians were the first to replace the lunar calendar with a calendar based on the solar year. They measured the solar year as 365 days, divided into 12 months of 30 days each, with five extra days at the end.
About 238 B.C. King Ptolemy II ordered that an extra day be added to every fourth year, similar to the modern leap year.
In ancient Greece a lunisolar calendar was in use, with a year of 354 days. The Greeks were the first to insert extra months into the calendar on a scientific basis, adding months at specific intervals in a cycle of solar years.
The original Roman calendar, introduced about the 7th century B.C., had 10 months with 304 days a year that began with March. Two more months, January and February, were added late in the 7th century B.C., but because the months were only 29 or 30 days long, an extra month had to be inserted approximately every second year.
The Roman calendar became hopelessly confused when officials to whom the addition of days and months was entrusted abused their authority and prolonged their terms of office.
In 45 B.C., Julius Caesar decided to use a purely solar calendar.
Caesar's calendar, known as the Julian calendar, fixed the normal year at 365 days and the leap year every fourth year at 366 days. The Julian calendar also established the order of the months and they days of the week as they exist in present day calendars.
In 44 B.C. Julius Caesar changed the name of the month Quintilis to Julius (July), after himself. The month Sextilis was renamed Augustus (August) in honor of the Roman emperor Caesar Augustus, who succeeded Julius Caesar.
Some authorities maintain that Augustus established the length of the months we use today.
The Julian year was 11 minutes and 14 seconds longer than the solar year. This discrepancy accumulated until by 1582 the vernal equinox occured 10 days early and church holidays did not occur in the appropriate seasons. Ten days were dropped. To prevent further displacement, the Gregorian calendar (named for Pope Gregory XIII) provided that century years divisible evenly by 400 should be leap years. The Gregorian calendar is used today throughout most of the world.