Solar eclipses in the same saros series repeat every 18 years 11 days 8 hours - and that extra 8 hours marches each eclipse's ground track about 120 degrees west of the last one. Step through the series below to watch the pattern.
Published figures: saros period 6,585.32 days (18 years 11 days 8 hours); each step shifts the ground track about 120 degrees west; a triple saros (exeligmos, 54 years 34 days) cancels the 8-hour remainder and returns the track near the same longitude (NASA GSFC eclipse catalog, F. Espenak).
Drag to orbit Earth and scroll or pinch to zoom. Step through the series with the slider or Play stepping, toggle all tracks at once, or jump straight 3 steps to see an exeligmos return.
Saros Cycle Eclipse Explorer 3D
This browser explorer steps through a saros series - the family of solar eclipses that repeat every 18 years 11 days 8 hours - and shows why each one's ground track lands about 120 degrees west of the last. Drag to orbit Earth, scroll to zoom, and scrub the slider to watch the pattern march around the globe.
The shift comes from that extra 8 hours: it means Earth has spun about a third of a turn further by the time the next eclipse in the series happens, so the shadow lands on a different part of the world. Step forward three times (an exeligmos, 54 years 34 days) and the three 8-hour remainders add up to about 24 hours - almost exactly one Earth rotation - so the track returns close to where it started.
- Step through up to 11 eclipses in a series with the slider or Play stepping
- Watch the ground track shift about 120 degrees west with every step
- Jump 3 steps at once to see an exeligmos return near the starting longitude
- Toggle all previous tracks at once to see the full westward march, or isolate just the current one
- Read the live facts panel for elapsed time, cumulative shift, and series length
- Runs fully in the browser with the vendored three.js engine - no account, no upload
| Figure | Published value |
|---|---|
| Saros period | 6,585.32 days = 18 years 11 days 8 hours |
| Westward shift per eclipse | about 120 degrees |
| Exeligmos (triple saros) | 54 years 34 days - returns near the same longitude |
| Eclipses per series | 69 to 87 |
| Series total lifespan | about 1,226 to 1,550 years |
| Source | NASA GSFC eclipse catalog (F. Espenak) |
Every saros series starts small near one of Earth's poles, grows into long central paths across the globe for many centuries, then shrinks and ends near the opposite pole as the geometry slowly drifts - this page focuses on the westward-stepping pattern within that long run, not the full multi-century growth-and-decay story. For a single eclipse's shadow-cone geometry and umbra path, see the Solar Eclipse 3D Explorer. For why eclipses group into two "seasons" a year in the first place, see Lunar Nodes & Eclipse Seasons.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached.
This is an educational approximation - every ground track on this page uses the same illustrative arc shape, rotated by the real longitude shift. It is not a reproduction of any single historical eclipse path or a live ephemeris.
Frequently Asked Questions
What is a saros cycle?
It is the period of about 18 years 11 days 8 hours after which the Sun, Moon and Earth return to nearly the same relative geometry, so a very similar eclipse happens again. Eclipses that repeat this way belong to the same numbered series.
Why does the eclipse path shift about 120 degrees west each time?
The saros period is not a whole number of days - it is 18 years 11 days and an extra 8 hours. In that extra 8 hours Earth keeps spinning, so the next eclipse in the series happens after the planet has turned about a third of a rotation further, landing the shadow about 120 degrees to the west.
What is an exeligmos?
It is a triple saros: three saros periods, or 54 years 34 days. Three of the 8-hour remainders add up to about 24 hours - almost exactly one full Earth rotation - so the eclipse track lands back near the same longitude it started from.
How long does a saros series last?
A single series typically produces 69 to 87 eclipses spread over roughly 1,226 to 1,550 years before Earth's slowly shifting geometry carries the series off the planet's disk entirely, per NASA's eclipse catalog.
Does this show a specific real eclipse's exact path?
No. Every ground track on this page uses the same illustrative arc shape, rotated by the real longitude shift between eclipses. It teaches the genuine westward-stepping pattern, not a reproduction of any single historical eclipse's precise path.
How is this different from the Solar Eclipse explorer?
The Solar Eclipse 3D Explorer teaches one eclipse's shadow-cone geometry - how the Moon's umbra sweeps a path across Earth during a single event. This page teaches the multi-decade pattern across many eclipses in the same series.