There’s a total eclipse of the sun coming up on March 20, 2015 – the day of the vernal equinox! EarthSky reader Billy asked:
Does the vernal equinox and the solar eclipse ‘just happen’ to occur on the same day? How often does this happen?
A total eclipse of the sun and the March equinox fell on the same date in 2015: March 20, 2015. The greatest eclipse occurred at 9:46 Universal Time, while the March equinox came to pass some 13 hours later at 22:45 Universal Time.
After this 2015 equinox eclipse, the next solar eclipse at the March equinox will happen on March 20, 2034. Then there will be two more in this century: 2053 and 2072.
Note the spacing of 19 years between these four eclipses of the March equinox sun.
Does that mean there are four solar eclipses coinciding with the March equinox every century? No. If you know anything about astronomy, you might have guessed that – here as in most sky-related phenomena – there are cycles acting within cycles. Want to know more? Keep reading …
A solar eclipse can only happen at new moon. For a solar eclipse to take place at the vernal equinox, therefore, the new moon must come on the equinox date. Of course, a March equinox new moon doesn’t always necessarily guarantee a solar eclipse. Here’s why.
New moons recur on (or near) the same calendar dates every 19 years. This 19-year lunar period is known as the Metonic cycle. Amazingly, you can project this 19-year cycle for centuries into the future (or past) to figure out when the new moon will occur on the March equinox.
For example, 11 Metonic cycles equal 209 years (19 years x 11 = 209 years).
Therefore, 209 years after March 20, 2015, the new moon and the March equinox will both take place on March 20, 2224. However, there won’t be a solar eclipse on March 20, 2224! As we just mentioned … a new moon on an equinox doesn’t guarantee an eclipse.
On the other hand, given any year that does have a solar eclipse on the March equinox – such as the year 2015 – it’s inevitable that this March equinox solar eclipse must belong to a series of four to five eclipses of the March equinox sun.
In other words, a solar eclipse is destined to fall on the March equinox once every 19 years for four or five straight Metonic cycles.
Sure enough, the March equinox solar eclipse on March 20, 2015, initiates a series March equinox solar eclipses that will conclude on March 19, 2072! (In 2072, the solar eclipse and March equinox will actually fall on March 19).
Series of March equinox solar eclipses:
March 20, 2015: Total solar eclipse
March 20, 2034: Total solar eclipse
March 20, 2053: Annular solar eclipse
March 19, 2072: Partial solar eclipse
So, Billy, that’s how we find that four years of the 21st century (2001-2100) feature a March equinox solar eclipse: 2015, 2034, 2053 and 2072.
From the best of our reckoning, there will be no solar eclipses taking place on the March equinox during the 22nd century (2101-2200) and 23rd century (2201-2300). However, there is an eclipse cycle called the Gregoriana whereby we can also expect the recurrence of a March equinox solar eclipse in a period of 372 years. It happens because, in a cycle of 372 years, the phases of the moon recur on (or near) the same weekdays and calendar dates. The eclipses (usually) fall on the same dates as well.
Hence, the next series of March equinox solar eclipses:
March 20, 2387: Partial solar eclipse
March 20, 2406: Total solar eclipse
March 20, 2425: Annular solar eclipse
March 19, 2444: Annular solar eclipse
March 20, 2463 Partial solar eclipse
And the previous series of March equinox solar eclipses:
March 19, 1624: Partial solar eclipse
March 20, 1643: Total solar eclipse
March 20, 1662: Total solar eclipse
March 20, 1681: Hybrid (Annular/Total) solar eclipse
As a side note, we wish to remind you that the year 2015 presented three Friday the 13ths. We find it quite intriguing that one Gregoriana period (372 years) afterwards – in the year 2387 – three Friday the 13ths occur on the same calendar dates as in 2015: February 13, March 13 and November 13.
Bottom line: We find four years of the 21st century (2001-2100) featuring a March equinox solar eclipse: 2015, 2034, 2053 and 2072. But that doesn’t mean that it happens four times in every century.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.