So my proposition is: the original Blue Moons were Full Moons that occured after the actual aequinox, so were the first Full Moons of Spring, and should have been recognised as Easter Moons: but in the reckoning of the ecclesiastic calendar they were the last Full Moons of Winter, and Easter was delayed by a month.
Table 1 below shows the situation in the years that the pamphlet was written.
| Year | Golden Number | Solstice (Jul.cal.) | FM 1 | FM 2 | FM 3 | Aequinox (Jul.cal.) | Belewe Moon? | Easter FM (Jul.cal.) | Ecclesiastic Moon |
|---|---|---|---|---|---|---|---|---|---|
| 1520 | 1 | 12 Dec 1519 | 04 Jan 1520 | 03 Feb 1520 | 04 Mar 1520 | 10 Mar 1520 | 03 Apr 1520 | 05 April | |
| 1521 | 2 | 12 Dec 1520 | 24 Dec 1520 | 22 Jan 1521 | 21 Feb 1521 | 11 Mar 1521 | 23 Mar 1521 | 25 March | |
| 1522 | 3 | 12 Dec 1521 | 13 Dec 1521 | 12 Jan 1522 | 10 Feb 1522 | 11 Mar 1522 | 12 Mar 1522 | 10 Apr 1522 | 13 April |
| 1523 | 4 | 12 Dec 1522 | 01 Jan 1523 | 31 Jan 1523 | 01 Mar 1523 | 11 Mar 1523 | 31 Mar 1523 | 02 April | |
| 1524 | 5 | 12 Dec 1523 | 22 Dec 1523 | 21 Jan 1524 | 19 Feb 1524 | 10 Mar 1524 | 19 Mar 1524 | 19 Mar 1524 | 22 March |
| 1525 | 6 | 11 Dec 1524 | 09 Jan 1525 | 08 Feb 1525 | 09 Mar 1525 | 11 Mar 1525 | 07 Apr 1525 | 10 April | |
| 1526 | 7 | 12 Dec 1525 | 29 Dec 1525 | 28 Jan 1526 | 27 Feb 1526 | 11 Mar 1526 | 28 Mar 1526 | 30 March | |
| 1527 | 8 | 12 Dec 1526 | 18 Dec 1526 | 17 Jan 1527 | 16 Feb 1527 | 11 Mar 1527 | 18 Mar 1527 | 16 Apr 1526 | 18 April |
| 1528 | 9 | 12 Dec 1527 | 06 Jan 1528 | 05 Feb 1528 | 06 Mar 1528 | 10 Mar 1528 | 04 Apr 1528 | 07 April | |
| 1529 | 10 | 11 Dec 1528 | 25 Dec 1528 | 24 Jan 1529 | 23 Feb 1529 | 11 Mar 1529 | 24 Mar 1529 | 27 March | |
| 1530 | 11 | 12 Dec 1529 | 15 Dec 1529 | 13 Jan 1530 | 12 Feb 1530 | 11 Mar 1530 | 13 Mar 1530 | 12 Apr 1530 | 15 April |
| 1531 | 12 | 12 Dec 1530 | 03 Jan 1531 | 01 Feb 1531 | 03 Mar 1531 | 11 Mar 1531 | 01 Apr 1531 | 04 April | |
| 1532 | 13 | 12 Dec 1531 | 23 Dec 1531 | 22 Jan 1532 | 20 Feb 1532 | 10 Mar 1532 | . . . . . . | 21 Mar 1532 | 24 March |
| 1533 | 14 | 11 Dec 1532 | 12 Dec 1532 | 11 Jan 1533 | 09 Feb 1533 | 11 Mar 1533 | 10 Mar 1533 | 09 Apr 1533 | 12 April |
| 1534 | 15 | 12 Dec 1533 | 31 Dec 1533 | 30 Jan 1534 | 28 Feb 1534 | 11 Mar 1534 | 29 Mar 1534 | 01 April | |
| 1535 | 16 | 12 Dec 1534 | 20 Dec 1534 | 19 Jan 1535 | 18 Feb 1535 | 11 Mar 1535 | 19 Mar 1535 | 19 Mar 1535 | 21 March |
| 1536 | 17 | 12 Dec 1535 | 08 Jan 1536 | 07 Feb 1536 | 07 Mar 1536 | 10 Mar 1536 | 06 Apr 1536 | 09 April | |
| 1537 | 18 | 11 Dec 1536 | 27 Dec 1536 | 26 Jan 1537 | 25 Feb 1537 | 11 Mar 1537 | 26 Mar 1537 | 29 March | |
| 1538 | 19 | 12 Dec 1537 | 16 Dec 1537 | 15 Jan 1538 | 14 Feb 1538 | 11 Mar 1538 | 15 Mar 1538 | 14 Apr 1538 | 17 April |
“FM” is Full Moon. Red dates fall between the actual winter solstice and 21 December; blue dates fall between the actual spring aequinox and 21 March: these are the original "Blue Moons". In 1524 and 1535, the real Full Moon fell on 19 March, also between the actual aequinox and 21 March: but the church computed them on 22 and 21 March (column "Ecclesiastic Moon") and thus accepted them as Easter Full Moons, and there was no delay of Easter, so these were not "betrayer" Moons. In 1533 the real Full Moon fell on 10 March, before the aequinox on 11 March, so was a genuine 4th Full Moon in winter.
A moon phase falls on the same calendar date again after 19 years (cycle of Meton), so based on the sequence number of the year in cycle – the so-called Golden Number (see second column) – people can predict the Moon's phases.
We see that within a 19-year cycle, it occurred 4 times (blue dates) that there were 4 Full Moons between the winter solstice and 21 March, in which the fourth Full Moon occurred after the actual spring aequinox – so should be regarded as the first Full Moon of spring – but that the church computation (column "Ecclesiastic Moon") would designate only the next Full Moon as the Paschal (Easter) Moon. So this supposedly "betrayer" (= blue) Full Moon is the real first Full Moon in spring, but was reckoned by the church to still fall in winter because it fell before 21 March and could not be the Paschal Moon.
It is not clear when the winter season was supposed to have started in the (ecclesiastic) calendar: maybe on 21 December, maybe on the 22nd (when the solstice occurs in most years of the Gregorian calendar that we now use), maybe with Christmas on the 25th. In any case these "Blue Moons" as listed in the table were the third in the winter season according to the calendar.
After the Gregorian reform (1582) had fixed the lunar calendar and synchronized the year with the seasons again, there would still occasionally be 4 Full Moons in a season, as is inherent in the 19-year cycle. Folklore in North America and elsewhere would have 12 traditional names for the Full Moons according to the season, but people would start using the term "Blue Moon" for any extra Full Moon. If they kept the traditional names for the Full Moons on either side of the turn of the season (e.g. "Lent Moon" the last Full Moon in winter, and "Easter Moon" the first in spring), then the third Full Moon in a season which has four would be counted as the extra "Blue Moon" – just as the "betrayer Moon" was the third in winter according to the old Julian calendar, and this convention was continued in the Famers' Almanac.