The Lunar solstice.

The lunar solstice was a term given by Alexander Thom to the observation that the azimuth of the rising Moon at the solstice, varies by roughly 20 degrees in 9 years.

This is because the moon travels around the earth on a path very close to the ecliptic, but the moon's path is angled by 5 degrees to the ecliptic.The time taken for the moon to travel from maximum height above the ecliptic to minimum and then back to maximum again is 27 days 5 hours and 5 min 35.8 s. As this does not correspond to one complete circuit around the earth, the crossing points- called 'nodes'- shift backwards each month. It takes 6793 days (18.631 years) for the nodes to return to their original position.

This means that for part of each month the Moon's path in the sky is 'higher' than the ecliptic, and then 'lower' than the ecliptic.


The ecliptic (created by the axial tilt of the Earth)  is 23.4 degrees above the east-west line on the earth, at midsummer and 23.4 degrees below the equator (the east-west line) at midwinter.

At the equinox, the sun is exactly on the east-west line, so the sun's angle to the equator (solar declination) is zero.

It takes one year for the earth to go around the sun.

It takes one month for the moon to go around the earth.

One month.
A node occurs when the moon crosses the ecliptic.

One earth year.
Not all months shown!

Due to precession of the lunar orbit, the two crossing points per month, the nodes, slowly move backwards around the ecliptic, taking 18.6 years, the nodal period, to complete one cycle.

The maximum angle the moon can be to the equator is (angle of ecliptic + or minus angle of Moon's inclination to ecliptic) 23.4 + 5 = 28.4 degrees. The Moon may be up to 28.4 degrees above, or below the ecliptic.

According to Alexander Thom the angle of the ecliptic in 1800 BC was 23.91 degrees and the angle of the moon to the ecliptic: 5:15 degrees.
( + or - 29. 06 degrees).

The last 'extreme' was in 2006.
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