Deciphering the heart of Saros cycles

Unravel the essence of Saros cycles by looking at their intensity peak. Discover how to access the heart of Saros cycles and why it matters.

What is a Saros cycle ?

Exactly 223 synodic months after an eclipse, a near similar eclipse will occur at the same place in the zodiac, a fact that has been known for more than two millennia. These two nearly identical eclipses occurring 18 years apart are said to belong to the same saros cycle (a saros being the time interval between two nearly identical eclipses). If you consider the chain of eclipses separated by 223 synodic months (a saros), they are said to belong to the same saros cycle (a Saros cycle can be about solar or lunar eclipses).

Every lunar and solar eclipses belong to a Saros cycle that spans throughout more than a millennium. At the very beginning of a Saros cycle, the sun, moon and earth are poorly aligned, resulting in partial eclipses. As time progresses, the Saros eclipses become more spectacular as the sun, moon, earth alignment improves and eclipses become total. Intensity reaches its climax when the three bodies are perfectly aligned. This is what I define as the culmination of the Saros cycle. Then, the perfect alignment relative to one Saros cycle gradually vanishes, its eclipses become partial again, then cease. This process, the rise, culmination and retraction of a Saros cycle spans over a millennium of years, and generally comprises 71-73 eclipses (figure 1).

saros intro fig 1

Figure 1. Saros 133 and the evolution of sun-earth-moon alignment (gamma) over time. Each point represents an eclipse. A value of gamma equals to zero means perfect alignment. This saros cycle spanned over 450’000 days (more than 1’200 years).

Bernadette Brady’s approach

Bernadette Brady, in her seminal work, recognised the potency and the magic of Saros cycles, and invited astrologers to interpret eclipses in the light of their corresponding Saros cycle. But how do you derive a chart for a Saros cycle ? She answered this question by looking at the signature chart of the very first eclipse of a Saros cycle, which can be seen as corresponding to the birth of the Saros cycle (figure 2).

saros intro - fig 2

Figure 2. Bernadette Brady’s approach is to take the first eclipse of a saros cycle (green circle), and compute the corresponding chart, said to represent the birth of the saros cycle.

After reading her above mentioned book (which I strongly recommend) and while listening to her podcast with Chris Brennan (also strongly recommended), something clicked within. I felt she successfully conveyed the magic and potency of Saros cycle. I could feel that something substantial was transmitted as she was talking. However, this feeling wasn’t present for me when I looked at the Saros signature she derived f(rom the first eclipse of a saros cycle) regarding my own natal eclipse. Similarly when Trump’s case was discussed in the podcast. I felt the substance was gone.

The heart of Saros cycles

This drove me to reconsider whether the substance of a saros cycle lied in its very first eclipse. While I understand the logic applied (the first eclipse can be seen as the birth of the saros cycle), I feel this can be debated in a number of ways. First, the sun, moon, earth alignment of the first eclipses is relatively variable across saros cycle, and in some cases, it might even be relatively subjective to classify them as eclipses or not. Second, on a more intuitive note, when you actually observe an eclipse, the core of the phenomenon seems to lie during its culmination (maximum occultation). Similarly with Saros cycle, I would argue that their essence lies when they culminate, i.e. when the sun, moon, earth are perfectly aligned and the eclipses are the most spectacular (figure 3).
saros intro - part 3

Figure 3. My approach is to estimate the point in time where the gamma value of a saros cycle equates zero (i.e. perfect sun-moon-earth alignment), thus denoting its culmination. The corresponding time estimate is highlighted in the green box (7 Feb 1856, Gregorian calendar, 9:43:43 UTC). The line in red is the gamma as a function of time function inferred by regression.

Reinterpreting eclipses using the culmination of their related saros cycles provided invaluable insights, including in the case Donald Trump’s famously born during a lunar eclipse, which will be partially discussed in an upcoming article. Meanwhile, all the culmination dates of Saros cycles (including the methodology to derive them, the related programming scripts, the guidelines to interpret them alongside examples and Donald Trump’s full case study is available here.

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