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The Secret To Predicting Total Solar Eclipses — Saros Cycle Explained

The total solar eclipse on April 8, 2024 comes hot on the heels on one in 2017, but it will be the last in the contiguous U.S. states until 2044 and 2045. Is there a pattern?

Look at a map of upcoming and recent solar eclipses (above) and they appear to occur randomly across Earth’s surface.

It’s an illusion born of the fact that humans have short lives. Solar eclipses are entirely predictable and occur in a strict, but complex pattern.

Mighty Pattern

There is a mighty pattern to solar eclipses that sees a very similar-shaped moon shadow projected onto Earth every 18 years, 11 days and eight hours as the sun, moon and Earth come into an almost identical alignment. It’s a period of time called a Saros—“the repetition.”

Two eclipses separated by a period of one Saros share a very similar geometry, according to EclipseWise, but over a long period of time produce partial, total and annular solar eclipses.

Eclipse Families

A Saros is a family of solar eclipses that are precisely 223 synodic months (synodic being the length of one orbit of the moon around Earth) or 6,585.3 days apart, according to NASA.

The total solar eclipse on April 8 in North America is part of Solar Saros 139, which last produced an event on March 21, 2006 that began in south America, crossed the Atlantic to North Africa, crossed the Mediterranean Sea to Turkey then passed through central Asia to end in Mongolia. The next one will occur on April 20, 2042 in southeast Asia.

It terms of the length and width of the path and the total totality time, the total solar eclipses of 2006 and 2024 are virtually identical.

MORE FROM FORBES18 Years Ago Today A Total Solar Eclipse Amazed Africa. It Repeats In 11 Days

Saros Cycle

There are approximately forty different Saros series in progress at any one time. Each solar eclipse resulting from the same alignments is a member of the same Saros.

The paths of all the eclipses in this same Saros resemble each other, but occur in different parts of the world. However, every third solar eclipse within the same Saros occurs in a very similar region of the world, with the path merely shifted north or south (depending on the Saros).

Paths Less Traveled

From the 18 years, 11 days and eight hours between each eclipse in the same Saros it’s that eight hours that pushes the path a third (120º) of the way around the globe traveling west.

Each Saros last many centuries, but begins and ends as a partial solar eclipse at the north or south pole, with the intervening period producing partial and central eclipses, both total and annular.

The Saros cycle was first discovered by the Babylonians, according to Sky and Telescope, and is partly how solar eclipses and the exact location of the path of totality can be predicted. Other factors include the erratic rate of Earth’s rotation.

For the very latest on the total solar eclipse—including travel and lodging options—check my main feed for new articles each day.

Wishing you clear skies and wide eyes.

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