What does the previous 12 months mean

The twelve months and their meanings

Solar calendar and phases of the moon

The Gregorian calendar used internationally today is a solar calendar. So it is primarily based on the length of the solar year and tries to reflect this as precisely as possible. A solar year is the period of time in which the earth completely circles the sun.

The phases of the moon do not play a role in this calendar system. Nevertheless, we divide the year into twelve months - time spans that were originally derived from the length of the lunar cycles, but no longer reflect this today.

Why are there months?

So why are there months in a solar calendar at all? Well, there are practical reasons for dividing the year into smaller time units. A full solar year is a rather cumbersome unit of time. In order to structure the long period of time, there are weeks, days - and even months.

Wolf moon, strawberry moon & Co: Old month and full moon names

Relic from Rome

However, the fact that we use months as the largest unit of time to subdivide the calendar year is due to the history of our calendar system. The month is a holdover from an early version of the Roman calendar and its predecessors. It is assumed that these were lunar calendars - calendars in which the length of the months was actually based on the lunar cycles.

Why is there seven days in the week?

Romans decoupled months from lunar phases

As a calendar concept, months have survived many centuries with countless calendar reforms - from the ancient lunar calendars of the Etruscans and early Romans to the lunisolar calendars of the Roman Empire to the Julian calendar, which was already a pure solar calendar and from the end of the 16th century to today common Gregorian calendar was derived.

In the Roman Empire, however, the length of the calendar months was decoupled from the actual phases of the moon. The first historically proven version of the Roman calendar already had months whose lengths no longer adhered to the duration of the lunar cycles.

No longer starts at the new moon

Today we live with a calendar system that is based on the course of the sun and at the same time is divided into time units that were originally based on the movement of the moon around the earth.

Although the original purpose of the months as the calendar equivalent of the lunar cycles is already in the designation month As can be seen, the months therefore no longer begin with the new moon or full moon. They also no longer reflect the lunar cycles in their length.

Why is there 12 months?

The number of months results from the astronomical conditions. An average lunar cycle, i.e. the period from one new moon to the next, lasts about 29.53 days. An average solar year lasts 365.24 days. This results in about 12.36 lunar months per solar year.

In the Roman calendar, the common year was therefore divided into twelve months (earlier versions only had ten months, although 61 winter days were not taken into account). Leap months were inserted at certain intervals so that it also reflected the solar year as precisely as possible. For this reason, we still add a leap day almost every four years.

Subjects: Time calculation, months, calendar