Note: This post was published originally in Spanish in this same blog. In an effort to ease enjoyment to English-speaking readers, I decided to translate it to my best ability into English. If there are grammar or lexicographical errors, please be kind to me.
I started my previous entry congratulating my friends Carolina Vólquez and Vicky Ledesma, as they (along with nearly 20 million other people around the globe) will have a birthday on August 21st. As most of you already know (and if you don’t, shame on you, shame! shame! shame!) in just six weeks we’ll experience a Total Solar Eclipse that will sweep the United Stated from coast to coast.
That got me thinking “how many solar eclipses had happened on my own birthday, May the 23rd?” One of the biggest advantages of astronomy is that we can go back and forth in time with extraordinary precision. Once you know the Moon and Earth orbits (and the position of the Sun), it only takes some number-crunching on those equations to determine facts that happened even when nobody was there to document them.
So I checked the immense and wonderful dataset Five Millennium Canon of Solar Eclipses: From -1999 to +3000, published by Fred Espenak and Jean Meeus for NASA. This resource offers a plain-text ASCII table that you can easily import into a data manager (you can use Excel, but bear in mind that it doesn’t play well with dates before the year 1900 or after year 2199).
This dataset contains detailed information on every single solar eclipse happening between 2000 BC and AD 3000 and they are exactly 11,898 eclipses! Here you have a summary of them all.
[table id=1 /]
Your Birthday Eclipses
So, I created a data visualization that focuses on your birthday date. Just choose your birthday month and day in the left-most upper boxes and the whole thing will update to show everything about that date. The map will show the exact point of “Greatest Duration” (the place where the eclipse lasted the longest). The right-most table will list every Total, Annular or Hybrid eclipse happening on that particular date, including a link to more detailed information at nasa.gov. Also, a breakdown of how many eclipses happened in each of the five millennium covered and a distribution per type.
You may select more than a month and more than a day, or none at all. Just keep in mind that the more ample the range, the more complex the visualization becomes. Also, at any time you may click in a bar in the millennium or the doughnut chart to focus on what you picked.
Would you please do me a favor? Share this post and show your friends your eclipses. I hope this could be a way to create awareness on astronomy and on our own planet. You may check the visualization on PowerBI clicking here (it’s in Spanish but you will get around easily).
In five millennia you have about 1.8 million days. If in that lapse only 11,898 eclipses will occur, means that only on the 0.651% of those days some kind of solar eclipse happened. What about Total Solar Eclipses? Just 0.1737% of the days over five millennium will see one. And this doesn’t account that most of those will happen in rural zones or in the middle of the ocean. Do you see how total solar eclipses, while considered common, are actually quite rare?
We should also have a word or two about calendars. The calendar system we use nowadays, called Gregorian Calendar, has only a little over 400 years in use, as it was first introduced on October 1582. Not wanting to enter the very interesting factoids that differenciate the Gregorian from its predecesor, the Julian Calendar, we should still note that dates before October 1582 are not computed exactly the same in History books due to the discrepancy between the two systems.
And so, it’s time for an anecdote: Isaac Newton, undoubtedly one of the brightests brains ever, was born in England on January 4th, 1643. Nevertheless, that date was computed in the Julian Calendar, as England didn’t adopt the Gregorian Calendar until 1752. That’s why on December 25 of 2014, Neil deGrasse Tyson joked a little saying on his Twitter feed: “On this day [Chistmas] long ago, a child was born who, by age 30, would transform the world. Happy Birthday Isaac Newton b. Dec 25, 1642”. January 4, 1643 in Julian equals December 25, 1642 in Gregorian.
Apart from these small facts, we still face a problem. Neither the Gregorian nor the Julian calendars included the “Year Zero”, and so Year 1 of our time is preceded by Year 1 before this era. This is awkward for time computations, and so Astronomers and other scientists use a different notation: The years should be preceded by a plus or minus sign, depending if they are in this side of the “Common Era” or before it, and thus, this notation included a Year Zero. So, using this system, the year AD 500 is +500 (or simply 500), while the year 500 BC equals the Year -499 in astronomical calculations.
So, the Canon uses both calendars with the astronomical notation. For eclipses that happened before October 15, 1582, dates are in the Julian Calendar. The rest are expressed using the Gregorian Calendar. The last eclipse registered under the Julian calendar was a Total, on June 20, 1582, crossing China. The first one under Gregorian calendar happened on Christmas Day of the same year, passing just South of Indonesia.
My final words are simple: Get into science! As the great Carl Sagan once said, “Astronomy is a humbling and character-building experience”. I urge you to join your local science or astronomy groups. You will learn huge amounts of wonderful stuff!