LunisticeLunistices are the most northerly and southerly moons of the month.
The lunar equivalent of solstices. More. positions on the horizon as measured by the Prehistoric Lunar Calendar
are an indirect pointer to the position of the nodes of the lunar orbit and thus to the time of year
at which a lunar eclipse may be expected to occur, as measured by the Prehistoric Solar Calendar.
In this schematic diagram:
- The 18.6 year lunar nodal cycle is represented by the outer circle and reads clockwise.
Each of its divisions is centred on the appropriate lunar event and represents a period of 1.16 tropical years, about 14 months.
- The annual solar cycle is represented by the inner circle and progresses anti-clockwise.
- During any lunar period, lunar eclipses may be expected to occur only in the months centred on
the events at either end of the adjoining solar axis; i.e. there are two possibly visible eclipses in any year.
- The fact that the "eclipse months" of the Prehistoric Solar Calendar overlap by a quarter-month
at each end is an important feature that allows the system to generally produce the correct answer
even though the natural cycles do not reconcile neatly.
Ancient observers, having solved the problem of knowing when a lunar eclipse might occur, would know from experience that there must either be a total eclipse, a partial eclipse or no visible eclipse. Could they have known which was most likely? Not completely impossible for, timing aside, on study of the data it would appear that eclipses occur in semi-regular patterns of fairly short duration. The typical, underlying, pattern seems to be two seasons of non-visible penumbral eclipses followed by two partials, two totals and then two more partials to end the sequence. Occasionally the penumbrals extend to three seasons in a row or reduce to one. The sequence of six visible eclipses sometimes reduces to five and may contain one, two or three totals, though it always begins and ends with a partial.
The main problem for a naked-eye observer with no theoretical knowledge is that not all visible eclipses can be seen, because they will sometimes occur when the moon is below the horizon. It must be said though that in any sustained period of observation and certainly several times in a human lifetime, eclipses would be observed that had started before the moon rose or were not completed before it set.
Therefore it would be possible to deduce that eclipses can happen when the moon is below the horizon. It was an essential part of these people's methodology that one can change the time and place of a rise or set by changing one's position on the earth's surface and, if desired, the same event may be observed repeatedly at different times from different places. So, while they could not be certain that an eclipse would actually be visible, they probably had a good idea of what to expect and they certainly knew when to expect it. Their methodology could not predict every eclipse perfectly but the overall pattern was mapped very well and it may be that their observational experience would have given better performance than seems immediately obvious to us.
This next diagram is a bit crude but: When lunistices are in the positions shown in the top row then an eclipse may be expected on any full moon that occurs when the sun is within either of the "eclipse months" shown on the bottom row.
Only the rises are shown here but the same is true of sets which are a mirror image.
The megalithic solar and lunar calendars were derived from survey data. After this had been done and further surveys continued to confirm these hypotheses, the big question became "Why did they do it that way?". The answer seems to be this previously unknown and unsuspected method of eclipse prediction. This was finally understood after studying several hundred years worth of prehistoric astronomical data calculated by NASA and relating that to the postulated prehistoric calendars.
- Calculation of general solar system data was done by NASA's Horizons Ephemeris.
- The prehistoric eclipse data came from Fred Espinak's Six Millennium Catalog of Lunar Eclipses
- Another useful link is Fred Espinak's Lunar Eclipses for Beginners.
- Thanks Fred.
With modern science we now know that an "eclipse season" (period within which an eclipse can occur) may vary between 31 & 38 days in width. This modern technical precision includes penumbral eclipses that are not visible to the human eye.