EPATTA. — From the Greek ἐπαγγελών (adding), it is the number that year by year and at a fixed moment indicates the excess of days in the solar year over the lunar year.
This excess increases by 11 units each year, so that the same new-moon cycle comes to fall 11 days earlier after one year, 22 days after two years, 33 after three, and so on. In practice, however, every three years the discrepancy is partly offset by the subtraction of 30 days, which form an extra (embolismic [v.]) month, so that the coincidence between the solar year and the lunar year is restored after 19 years. On this principle the epact is related to the golden number and is shown in certain tables, which, however, are not of perpetual validity, since the excess in question is not exactly 11 days. From 1900 to 2109 the following table is in force:
| 1 | 20 | 11 | 19 |
The computation of the epact generally begins on 10 January, so that the figures apply throughout the year; some computists, however, reckoned it from another date, especially from 10 September. V. PASQUA.