About a “world” calendar
What is a Calendar?
Every system of calculation which divides time into days, months, years in accordance to the constant, periodic phenomena of the Earth spin round its axis, the Earth revolution round the Sun and the Moon revolution round the Earth, to achieve an organization in public and religious life and to serve different scientific and historical needs. There are lunar/solar/ancient greek/ chinese/ arabic calendars.
Therefore, every calendar is an instrument which classifies past or future events. But, first and foremost, it is a study of the sky(ουρανός->ouranio). The solar, earth and lunar motions are eternal, fixed reference points for the earthly time sense.