Saros-Inex Panorama Kyler Olsen

The Saros-Inex Panorama is an unique graph that shows the cyclical nature of eclipses. The cyclical nature of eclipses arises from the conditions required for an eclipse. For a solar eclipse, first the Moon must be near the New Moon phase. The Moon's orbit however is inclined relative to the ecliptic of the Solar System, so second, the Moon must be passing through the ecliptic. Furthermore, the Moon's orbit is not a perfect circle, leading to some eclipses being an annular eclipse, with others being a total eclipse. Each of these can be tracked using a different lunar month.

Synodic Month The average time between one Moon phase and the same Moon phase in the next lunar cycle (29 days, 12 hours, 44 minutes).
Lunar Nodes The two points in the Moon’s orbit where it intersects the ecliptic of the Solar System.
Draconic Month The average time it takes the Moon to orbit from one node to the same node (27 days, 5 hours, 6 minutes).
Apsis A point of extreme in an orbit, ie. the closest or furthest point of the Moon from the Earth.
Anomalistic Month The average time it takes the Moon to orbit from one apsis to the same apsis (27 days, 13 hours, 19 minutes).

Each of these lunar months have a different period. An eclipse happens when specifically the synodic and draconic months line up. If the anomalistic month also lines up, we then know that it will be the same type of eclipse. Unfortunate they don’t perfectly line up, but they do come close every 6 synodic months, which is about 6 1/2 draconic months. This is the amount of time that occurred between the October 2023 Annular Eclipse and the April 2024 Total Eclipse. This is not exact, so a solar eclipse won’t happen every six months.

Even closer, every 223 synodic months is just under 242 draconic months and just under 239 anomalistic months. This period of time is called a saros. This means if a solar eclipse happens on a given date, one saros later, a similar solar eclipse will likely happen again some where on Earth. This isn’t exact, but you can expect about 70 eclipses, each 223 synodic months apart, in what is called a saros series. Every saros during the series, the draconic and less so the anomalistic months will drift, with the first and last several being only partial eclipses visible in the polar regions. Multiple saros series will be progressing at any given time.

There are many other eclipse cycles, but the second most interesting, especially when talking about the saros is the inex. Every 358 synodic months is very close to 388 1/2 draconic months. Also an eclipse one inex later will be in the next saros series, and vise versa, making it straight forward to graph, creating the saros-inex panorama.

Data Source

The primary data source for my interactive saros-inex panorama is NASA's Five Millennium Catalog of Solar Eclipses. The images shown in the corner are also from NASA's Eclipse Website when available. I hope to in the future increase the number of eclipses included and generate my own images.

Other cycles in the Saros-Inex panorama

An interesting thing also begins to occur when you look at certain multiple combinations of saros and inexes. For example if you subtract 8 saros from 5 inexes, you will get 6 synodic months.

$5 \times 358 - 8 \times 223 = 1790 - 1784 = 6$

This means that if you find the October 2023 eclipse on the panorama, go to right 5 columns, then up 8 rows, you will find the April 2024 eclipse. You can find other formulas for other eclipse cycles on Wikipedia.