Saros Eclipse Cycle

By Ginger Wentrcek

Every 18 years, 11 days, and 8 hours, a cycle of eclipses, called the Saros Cycle, repeats itself. In that period of time, the sun, moon, and earth's line of nodes will once again be in almost the same positions they were 18 years, 11 days, and 8 hours, or 6585 days, ago. This fact was discovered by Babylonian astronomers about two millennia BC.

You can read a much more detailed explanation about eclipses and the Saros Cycle, how to determine the beginning of a Saros Cycle, and how to determine the location of a given eclipse on NASA's website.

October 14, 2023 - Annular Solar Eclipse

Let's look at the upcoming annular solar eclipse which will occur on October 14, 2023, and check the rule to determine the date of the previous annular solar eclipse in the Saros Cycle.

Using the Date Calculator from TimeandDate.com, subtract 6,585 days from October 14, 2023. The result is October 3, 2005.

Checking records of previous annular eclipses, EclipseWise.com indicates there was an annular solar eclipse on October 3, 2005.

August 21, 2017 - Total Solar Eclipse

Let's check another example.

According to NASA, there was a total solar eclipse on August 21, 2017. From that date, subtract 6,585 days.

Using the Date Calculator from TimeandDate.com , 6585 days prior to that date was August 11, 1999.

NASA verifies that there was a total solar eclipse on that date, exactly 6585 days prior to August 21, 2017.

November 8, 2022 - Total Lunar Eclipse

We'll try one last eclipse to test the rule, but this time, a lunar eclipse example will be used.

According to NASA records, there was a total lunar eclipse on November 8, 2022, and if the rule holds true, there should have been a total lunar eclipse 6585 days prior to that, which would have been October 28, 2004. Using TimeandDate's Date Calculator, that would fall on October 28, 2004. Was there a lunar eclipse on October 28, 2004? Yes, You can read NASA's article here