Golden numbers
A golden number is a number assigned to each year
A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....

 in sequence to indicate the year's position in a 19-year Metonic cycle
Metonic cycle
In astronomy and calendar studies, the Metonic cycle or Enneadecaeteris is a period of very close to 19 years which is remarkable for being very nearly a common multiple of the solar year and the synodic month...

. They are used in the computus
Computus is the calculation of the date of Easter in the Christian calendar. The name has been used for this procedure since the early Middle Ages, as it was one of the most important computations of the age....

 (the calculation of the date of Easter
Easter is the central feast in the Christian liturgical year. According to the Canonical gospels, Jesus rose from the dead on the third day after his crucifixion. His resurrection is celebrated on Easter Day or Easter Sunday...

) and also in the Runic calendar
Runic calendar
A Runic calendar is a perpetual calendar based on the 19 year long Metonic cycle of the Moon. Runic calendars were written on parchment or carved onto staves of wood, bone, or horn. The oldest one known, and the only one from the Middle Ages, is the Nyköping staff, believed to date from the 13th...

. The golden number of any Julian
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...

 or Gregorian
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...

 calendar year can be calculated by dividing the year by 19, taking the remainder, and adding 1. (In mathematics this can be expressed as (year number modulo
Modulo operation
In computing, the modulo operation finds the remainder of division of one number by another.Given two positive numbers, and , a modulo n can be thought of as the remainder, on division of a by n...

 19) +1.)

For example, divided by 19 gives , remainder . Adding the number before to the number that you are using gives a golden number of .

The term golden number is first documented in Hildegard of Bingen
Hildegard of Bingen
Blessed Hildegard of Bingen , also known as Saint Hildegard, and Sibyl of the Rhine, was a German writer, composer, philosopher, Christian mystic, Benedictine abbess, visionary, and polymath. Elected a magistra by her fellow nuns in 1136, she founded the monasteries of Rupertsberg in 1150 and...

's Ordo Virtutum
Ordo Virtutum
Ordo Virtutum is an allegorical morality play, or liturgical drama, by Hildegard of Bingen, composed c. 1151...

(ca. 1151) and in the computistic poem Massa Compoti by Alexander de Villa Dei in 1200. Later, a scribe added it to tables originally composed by Abbo of Fleury
Abbo of Fleury
Abbo of Fleury , also known as Abbon or Saint Abbo was a monk, and later abbot, of the Benedictine monastery of Fleury sur Loire near Orléans, France....

in 988.
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