Photo credit: Oliver Floyd
There’s a total eclipse of the sun coming up on March 20, 2015 – the day of the vernal equinox! EarthSky reader Billy asked:
A total eclipse of the sun and the March equinox do fall on the same date this year: March 20, 2015. The greatest eclipse occurs at 9:46 Universal Time, while the March equinox comes to pass some 13 hours later at 22:45 Universal Time.Does the vernal equinox and the solar eclipse ‘just happen’ to occur on the same day? How often does this happen?
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 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 …
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A total solar eclipse is nature’s grandest spectacle. This composite image is the total solar eclipse of August 1999 by eclipse master Fred Espenak.
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.
Why aren’t there eclipses at every full and new moon?
A total solar eclipse can be seen only along a narrow pathway across Earth’s surface. In the case of the March 20, 2015 eclipse that pathway cuts east of Iceland, across the North Atlantic. Click here to learn more about the total eclipse. Map via Fred Espenak
Contrasting a total solar eclipse (A) annular eclipse (B) and partial solar eclipse (C). Image credit: Wikimedia Commons
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 March equinox solar eclipses.
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:
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.March 20, 2015: Total solar eclipse
March 20, 2034: Total solar eclipse
March 20, 2053: Annular solar eclipse
March 19, 2072: Partial solar eclipse
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 the same calendar dates. If an eclipse is involved, the eclipse will (usually) fall on the same date 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
Parts of the world will see a partial eclipse on March 20, 2015. Click here to learn more about the partial eclipse. Map via Fred Espenak
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.
Solar eclipses: 2001 to 2100
Phases of the moon: 2001 to 2100
Solstices and equinoxes: 2001 to 2100
Equinox and solstice calculator
Thanks to: http://earthsky.org