
24. The Calendar
As far back as 30,000 years ago, The phases of the Moon have been used as a timepiece. Bones with the notches on them to indicate the Moon phases, known as tally sticks, are thought to be the first evidence of a calendar.
The 30-day month calendar is based on the cycles of the Moon. Since ancient Greece, the Moon has been used as a marker of the month. Many cultures have used this sighting of the crescent Moon to determine the start of a month. The contrast to the lunar calendar is the solar, or Gregorian, calendar which is the standard calendar used around the world.