Because it takes approximately 88 days to go from maximum alignment of the Moon's orbit to maximum misalignment, then knowing that there was a total lunar eclipse on the evening of January 20/morning of January 21 and that the equinox is on the evening of March 20 (or the morning of March 21) allows you to do that key calculation.There are 59 days between January 21 and March 21, but it takes 88 days to go from maximum alignment to maximum misalignment. So take that measured angular misalignment, divide it by the sin((59/88)*90°) that occurred from the prior lunar eclipse until today's full moon, and that's the tilt of the Moon's orbit!

Because it takes approximately 88 days to go from maximum alignment of the Moon's orbit to maximum misalignment, then knowing that there was a total lunar eclipse on the evening of January 20/morning of January 21 and that the equinox is on the evening of March 20 (or the morning of March 21) allows you to do that key calculation. There are 59 days between January 21 and March 21, but it takes 88 days to go from maximum alignment to maximum misalignment. So take that measured angular misalignment, divide it by the sin((59/88)*90°) that occurred from the prior lunar eclipse until today's full moon, and that's the tilt of the Moon's orbit!

Because it takes approximately 88 days to go from maximum alignment of the Moon’s orbit to maximum misalignment, then knowing that there was a total lunar eclipse on the evening of January 20/morning of January 21 and that the equinox is on the evening of March 20 (or the morning of March 21) allows you to do that key calculation.

There are 59 days between January 21 and March 21, but it takes 88 days to go from maximum alignment to maximum misalignment. So take that measured angular misalignment, divide it by the sin((59/88)*90°) that occurred from the prior lunar eclipse until today’s full moon, and that’s the tilt of the Moon’s orbit!