Navigation using the Epact
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Which treats of the golden numbers of Saros, showing the Epact, and thus the age of the Moon.
It is convenient and necessary for Seafarers to know both the Prime or Golden number, and the Epact, which shows the age of the moon or its change day within 12 hours either way; and by the age of the Moon, you may know at what time it rises, and wherever you know what bearing of Moon makes high water, you will also know when it will reach that bearing, and so reckon the behaviour of the tides at any time of day or night; therefore it is important to know the Epact, and also that which is the Golden number.
The Epact
The Epact is the day of the month where the Full Moon should lie, if it is not overly affected by your longitude, or by the Golden Number, and the change day of the Moon is the day it is New, and is 14 days from the Epact. It decreases by two days for each month from the beginning of summer, and another day for each season change, for the Full Moon occurs every 28 days, more or less. Also it has previously been mentioned that for every 15 degrees you find yourself West of Tycho City an hour is lost, and an hour is likewise gained for every 15 degrees you travel to the East.
- Finding the Epact
| Month | Epact | Change |
|---|---|---|
| -- | Beltane | Samhain |
| Meadow | 28 | 14 |
| Heat | 26 | 12 |
| Breeze | 24 | 10 |
| Fruit | 21 | 7 |
| Harvest | 19 | 5 |
| Vintage | 17 | 3 |
| Frost | 14 | 28 |
| Snow | 12 | 26 |
| Ice | 10 | 24 |
| Thaw | 7 | 21 |
| Seed | 5 | 19 |
| Blossom | 3 | 17 |
The Golden Number
The Golden number is the timing of the dragon Saros, in that he moves the Moon differently each year. The last year with a Golden number of 1 was 793 WK, and the number increments by seven every year, with 18 being subtracted from it each time it grows too high; and therefore 811 WK is the next year with a Golden number of 1. This number is used to look up the value of the Draconic regression and Anomalistic progression of the Moon, from which the Epact is adjusted. The Golden Number works in a complex manner measuring the various epicycles, and it is long and tedious to calculate its influence, so instead I present some prepared tables for each Year, based on its Golden Number.
- Finding the Golden Number
| Year | Golden # |
|---|---|
| 807 | 9 |
| 808 | 16 |
| 809 | 5 |
| 810 | 12 |
| 811 | 1 |
| 812 | 8 |
| 813 | 15 |
| 814 | 4 |
| 815 | 11 |
| 816 | 18 |
| 817 | 7 |
| 818 | 14 |
| 819 | 3 |
| 820 | 10 |
| 821 | 17 |
| 822 | 6 |
| 823 | 13 |
| 824 | 2 |
| 825 | 9 |
To find the time of the Full and New Moon, consult the Epact charts. Below is the Epact Chart for Seagate in 808WK.
- The Epacts for Seagate 808WK
| Date | Time | Sun Alt | Sun Bearing | Moon Alt | Moon Bearing | Distance | Type |
|---|---|---|---|---|---|---|---|
| Beltane | 00:00 | -36°20' | 4°54' | 38°53' | 182°40' | 177°21' | Full Moon |
| 14 Meadow | 18:20 | 5°38' | 291°09' | 5°15' | 290°28' | 0°47' | New Moon |
| 28 Meadow | 00:50 | -28°56' | 15°40' | 32°31' | 196°32' | 177°01' | Full Moon |
| 13 Heat | 05:10 | 5°10' | 64°19' | 0°31' | 65°32' | 4°47' | New Moon |
| 26 Heat | 04:15 | -5°39' | 55°28' | 7°58' | 239°22' | 176°16' | Full Moon |
| 11 Breeze | 05:30 | 5°07' | 67°28' | 0°18' | 71°38' | 6°22' | New Moon |
| 24 Breeze | 05:00 | -2°51' | 64°43' | 4°25' | 249°03' | 176°14' | Full Moon |
| 8 Fruit | 06:05 | 6°20' | 77°39' | 0°28' | 81°49' | 7°12' | New Moon |
| 21 Fruit | 03:15 | -27°15' | 52°13' | 28°35' | 235°27' | 177°35' | Full Moon |
| 5 Harvest | 17:55 | 5°13' | 270°36' | 0°05' | 270°03' | 5°10' | New Moon |
| 19 Harvest | 00:50 | -53°11' | 18°32' | 53°41' | 199°07' | 179°53' | Full Moon |
| 3 Vintage | 17:30 | 1°50' | 259°27' | 0°21' | 259°10' | 1°31' | New Moon |
| 17 Vintage | 01:45 | -55°29' | 50°48' | 54°31' | 228°56' | 178°07' | Full Moon |
| Samhain | 17:00 | 0°48' | 248°13' | 1°58' | 249°36' | 1°49' | New Moon |
| 14 Frost | 06:45 | -2°56' | 113°08' | 0°33' | 291°11' | 176°42' | Full Moon |
| 28 Frost | 16:45 | 0°10' | 241°11' | 3°08' | 244°43' | 4°36' | New Moon |
| 12 Snow | 17:15 | -5°17' | 244°27' | 0°50' | 66°58' | 174°51' | Full Moon |
| 26 Snow | 13:30 | 26°41' | 202°08' | 32°09' | 205°35' | 6°15' | New Moon |
| 10 Ice | 17:20 | -3°53' | 246°23' | 0°26' | 71°03' | 173°50' | Full Moon |
| 24 Ice | 07:35 | 5°42' | 117°45' | 10°16' | 114°29' | 5°35' | New Moon |
| 7 Thaw | 17:40 | -3°26' | 255°15' | 0°15' | 79°28' | 174°16' | Full Moon |
| 21 Thaw | 06:30 | 0°09' | 101°34' | 0°31' | 97°11' | 4°24' | New Moon |
| 5 Seed | 18:05 | -3°56' | 268°26' | 0°19' | 90°08' | 175°50' | Full Moon |
| 18 Seed | 17:45 | 2°07' | 270°16' | 0°04' | 271°01' | 2°12' | New Moon |
| 3 Blossom | 18:25 | -3°16' | 281°41' | 0°08' | 100°29' | 177°08' | Full Moon |
| 16 Blossom | 18:05 | 3°01' | 282°47' | 1°53' | 280°06' | 2°54' | New Moon |
