Tag: anomalistic month

The Best Eclipse Cycle

The anniversary of the Octon (4 eclipse years in 47 lunar months) did not provide similar eclipses and so, by counting more than four, the other motions of the Moon could also form part of that anniversary. This is especially true of the anomalistic month, which changes the changes the apparent size of the Moon within its phase cycle, recreate the same type of lunar eclipse after nineteen eclipse years. This 18 year and 11 day period is now taken as the prime periodicity for understanding eclipse cycles, called the Saros period – known to the Babylonian . The earliest discovered historical record of what is known as the saros is by Chaldean (neo-Babylonian) astronomers in the last several centuries BC.

The number of full moons between lunar eclipses must be an integer number, and in 19 eclipse years there are a more accurate 223 lunar months than with the 47 of the Octon. This adds up to 6585.3 days but the counting of full moon’s is obviously ideal as yielding near-integer numbers of months.

We noted in a past post that the anomalistic month (or AM), regulating the moon’s size at full moon, has a geometrical relationship with eclipse year (or EY) in that: 4 AM x pi (of 3.1448) equals the 346.62 days of the eclipse year as the circumference. Therefore, in 19 EY the diameter of a circle of circumference 19 x 346.62 days must be 4 x 19 AM so that , 76 AM x pi equals 223 lunar months, while the number of AM in 223 lunar months must be 239; both 223 and 239 being prime numbers.

Continue reading “The Best Eclipse Cycle”

The Strange Design of Eclipses

We all know about solar eclipses but they are rarely seen, since the shadow of the moon (at one of its two orbital nodes) creates a cone of darkness which only covers a small part of the earth’s surface which travels from west to east, taking hours. For the megalithic to have pinned their knowledge of eclipses to solar eclipses, they would have instead studied the more commonly seen eclipse (again at a node), the lunar eclipse which occurs when the earth stands between the sun and the moon and the large shadow of the earth envelopes a large portion of the moon’s surface, as the moon passes through our planet’s shadow.

This phenomenon of eclipses is the result of many co-incidences:

Firstly, if the orbit of the moon ran along the ecliptic: there would be a solar eclipse and a lunar eclipse in each of its orbits, which are 27 and 1/3 days long.

Secondly, if the moon’s orbit was longer or shorter, the angular size of the sun would not be very similar. The moon’s orbit is not circular but elliptical so that, at different points in the lunar orbit the moon is larger, at other points smaller in angular size than the sun. This is most visible with solar eclipses where some are full or total eclipses, and others eclipse less than the whole solar disc, called annular eclipses.

Thirdly, the ecliptic shape of the moon’s orbit is deformed by gravitational forces such as the bulge of the earth, the sun and planets so that its major axis rotates. When the moon is furthest away (at apogee), its disc exceeds that of the sun. And when the moon is nearest to the earth (at perigee), its disc is smaller than that of the sun. This type of progression is called the precession of the lunar orbit where the major axis travels in the same direction as the sun and moon. This contrasts with the precession of the lunar nodes which also rotate (see later).

Continue reading “The Strange Design of Eclipses”