Astronomical calendar

An astronomical calendar is a calendar that is not defined by arithmetic rules (→ arithmetic calendar ), but by astronomical events such as the phases of the moon , the positions of the sun , the rising and setting of celestial bodies or their positions, the autumn or spring equinox or a combination thereof .

Solar calendar

The solar calendars are based on the course of the earth, which means that, for example, every beginning of the year coincides with the same position of the earth in the solar system. The calendars are called solar calendars (and not earth calendars) because the sun seems to be moving on the ecliptic while the earth is actually moving. A solar calendar is determined by the observation of the 4 years of data vernal equinox (spring day-and-night same ), the summer solstice , the fall point (Autumn day and night are equally), winter solstice determined. An essential question with the individual solar calendars is the determination of the beginning and end of the year. ( see also solar year , solar cycle )

Examples:

• Zoroastrian calendar
• Julian calendar
• Gregorian calendar
• French Revolutionary Calendar (from August 24, 1795 , based on the Gregorian calendar)
• Soviet revolutionary calendar (based on the Gregorian calendar)

Lunar calendar

Synodic lunar calendar

In contrast to the solar calendars, the synodic lunar calendars are based exclusively on the phases of the moon . The months are coordinated with the phases of the moon, which are particularly easy to perceive. However, since a year cannot be divided by a number of phases of the moon, a year in a lunar calendar is too short or too long. That means, the beginning of the year shifts with the years.

In principle, however, the observation of the phases of the moon with their period of 29.53 days is difficult, because the phase can only be precisely determined visually with a crescent moon (this is where the month began in the Celtic calendar ). Even the full moon is difficult to make out to the exact day. The new moon (also black moon ) is inherently unobservable. The first "sickle" (ancient times called this "new moon" or " new light ", here the Persians let the month begin) only shows up one or sometimes two days after the new moon, so that it is not suitable for determining the exact day from Not to mention the visibility conditions of the weather. In ancient Babylonia , Jerusalem and Rome, the determination of the “new moon” was consequently the responsibility of special priests and was proclaimed with horns and trumpets. In ancient Egypt , the beginning of the Egyptian lunar calendar (despite the name not a pure lunar calendar) was based on the last old light sighting.

Examples:

• Roman calendar
• Islamic calendar (civil)

Sidereal lunar calendar

In a very early period, presumably as early as the Paleolithic Age , the position of the moon in front of the respective fixed star sky ( zodiac sign ) was used as a basis. Because the moon shows its position against the background of the starry sky to the day. Corresponding to the sidereal period of rotation of 27.32 days, the ancient Chinese and Arabic astrology, in the oldest parts of the ancient Indian Rgveda from the 2nd millennium BC , was already familiar . Called "houses", 27 different positions, according to which each day of the lunar month could be precisely determined. A 28th day came late. From this the sidereal lunar year of 355 days and 13 months of 27 days, which in turn was divided into 3 weeks of nine days, was formed. This lunar year does not correlate with the solar year, the sidereal month does not correlate with the phases of the moon. The seasons shift gradually, which is not a problem for nomadic peoples such as the hunters and gatherers in the Paleolithic. The sidereal lunar calendar is the oldest form of calendar ever and represents a pure lunar calendar.

The sidereal lunar calendar lives on especially among nomadic peoples and in the astrological calendars of the ancient peoples.

Examples:

• Rigveda
• Chinese astrology
• Arabic astrology

Lunisolar calendar

In the lunisolar calendar (Luna = moon, Sol = sun), as in the lunar calendar, the months are based on the phases of the moon . However, so that the annual data does not shift, leap months are inserted according to certain rules .

Examples:

• Jewish calendar
• Thai lunar calendar
• Tibetan calendar
• Chinese calendar
• Hindu calendar

Stellar calendar

The following paragraph is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.

So far there is no evidence for “stellar calendars”. There are, however, lunistellars.

With the stellar calendar, the annual dates are based on the position of the stars . In this calendar form, the sun and moon play subordinate roles and are seasonally adapted to the respective star positions.

Examples:

• Egyptian Sothis calendar - year begins with the heliacal rising date of Sirius
• Coptic calendar
• Mayan Calendar

See also

• List of calendar systems

Web links

Wikibooks: Astronomical Calculations for Amateurs / Calendars  - Learning and teaching materials

Individual evidence

1. ↑ Joachim Friedrich Quack: Between the sun and the moon - time calculation in ancient Egypt , original publication in: H. Falk (ed.), From the ruler to the dynasty. On the nature of continuous calculation of time in antiquity and the present , Bremen 2002, p. 38, pdf.