The American Church Dictionary and Cycopedia
The Golden Number is that which marks the position of any given year in the Lunar Cycle, which is a period of nineteen years. Meton, an Athenian philosopher, discovered that, at the end of every such period, the new moons take place on the same days of the months whereon they occurred before its commencement. This discovery was considered to be so important, it became the custom to inscribe the rule for finding the moon's age on a tablet in golden letters and placed in the market-place at Athens; hence arose the term Golden Number. The Golden Number may be found by adding one to the year of our Lord, and dividing the sum by 19, when the remainder, if any, is the Golden Number. If there be no remainder, the Golden Number is 19. One is added to the year of our Lord because the first year of the Christian era was the second of the Cycle. The time of Easter may be found by means of the Golden Number. (See Tables in Prayer Book.)
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Miller, William James. Entry for 'Golden Number'. The American Church Dictionary and Cyclopedia. https://www.studylight.org/dictionaries/eng/acd/g/golden-number.html. 1901.