EPATTA. - From the Greek ἐπάγειν (to add), it is the number that indicates, from year to year and at a given moment, the excess in days of the solar year over the lunar year.
This excess increases by 11 units each year: thus the same new moon falls 11 days earlier after 1 year, 22 after 2 years, 33 after 3, and so on. In practice, however, every three years the difference is partly cancelled by the subtraction of 30 days, which form an intercalary month (endolionale [v]), so that the coincidence between solar year and lunar year is restored after 19 years. On the basis of this principle, the e. is related to the golden number and indicated in certain tables, which nevertheless do not have perpetual validity, since the excess mentioned above is not exactly 11 days. From 1900 until the end of 2199, the following table is in force:
| golden number | epact | golden number | epact |
|---|---|---|---|
| 1 | 20 | 11 | 19 |
| 2 | 10 | 12 | null epact |
| 3 | 21 | 13 | 11 |
| 4 | 2 | 14 | 22 |
| 5 | 13 | 15 | 3 |
| 6 | 24 | 16 | 14 |
| 7 | 5 | 17 | 25 |
| 8 | 16 | 18 | 6 |
| 9 | 27 | 19 | 17 |
| 10 | 8 |
The calculation of the e. is generally made to begin on 1 Jan., so that the relevant figures apply throughout the year; however, some computists reckoned it from another date, especially from 1 Sept. V. PASQUA.