Thread by @krishashok

This year, there’s a good chance that (some of) your parents or grandparents have been furiously reaching out to “experts” on WhatsApp, YouTube and TV to find out if Pongal/Makar Sankranti was to be celebrated on Jan 14 or Jan 15.

The confusion stems from the fact that this year, the Sun enters the zodiac sign of Capricorn in the afternoon of the 14th, and since people like to celebrate their festivals in the morning, some “experts” have been recommending celebrating Pongal on the 15th

At this point, people who believed that they were born with the sun sign of Capricorn are going “Eh? What do you mean the sun is casually ambling into Capricorn on Jan 14th afternoon? I was born on Jan 4 and was told I’m Capricorn!"

"How can I be Capricorn if the sun is ringing the Capricorn house doorbell on Jan 14th afternoon?”. I have some news for you. I mean, not you Capricorn folks. The Sankranti/Pongal date debate folks.

But before I deliver the aforementioned news, I have to preface it with a longish story.

Some 5000 years ago, the Egyptians felt a need to measure time accurately enough to be able to predict when the Nile will flood every year because, well, their civilisation depended on it

Every civilisation invented its own calendar system to keep track of the seasons. It is also estimated that some 3000 years ago, the Vedic calendar that is the basis for most traditional calendars in India was instituted

But before we proceed further, let’s understand that there are 2 ways to measure a year - the sidereal year and the tropical year.

If you take a fixed point in the sky (say, perhaps a particular star) and then measure a year on the basis of when the earth returns to the exact same reference point, you get a sidereal year.

The tropical year is measured by measuring the time elapsed between 2 spring (or autumn) equinoxes. Equinoxes are days when the day and night are roughly the same all over the planet.

As you might imagine, the tropical year is more likely to be in actual sync with the seasons, but to understand why we have to dig a little deeper.

Around 200 BCE, the Greeks observed that the Babylonian/Sumerian calendar from 2000 years before the Greeks seemed to be out of sync with the Greek calendar, but to understand why, we have to go back to high school science.

In school, we are all taught about 2 kinds of movement that our planet 🌎 engages in

1. It revolves around the sun in a slightly flattened circular orbit once in 365 and a quarter days
2. It rotates on its axis every 24 hours.

We also know that this axis isn’t perpendicular but tilted (in reference to the plane of the sun and the earth) by 23.5 degrees

And this tilt is why we have seasons. For instance, when the northern hemisphere is tilted towards the sun, it receives more heat from the sun and thus it’s summer.

PS: It's not because the earth is closer/farther to the sun. In fact, the sun is closest to the earth in January

Now that we have the basics of how the earth moves in these 2 ways (rotation and revolution), let’s understand the third kind of motion. The earth wobbles. (Picture for representation only)

Yes. It wobbles on its axis. It’s not a championship ice skater pirouetting with precision around the rink. It’s a 4.5 Billion-year-old, drunk, retired ballerina. Every ~25,000 years, its axis changes from its current angle all the way to the other side

This wobble is called the precession of the equinoxes. In simpler teams, the days of the year when it’s the longest day/night (solstices) or equal day and night (equinox) keeps changing as the earth wobbles over the centuries

Now let’s back to the Egyptians, Greeks and ancient Indians. The thing is - the Greeks discovered that the older Babylonian calendar was out of sync with theirs and since their calendar was based on the Egyptian tropical calendar, they made adjustments

And in fact, the Gregorian calendar we use today around the world is derived from the Greek (and by extension, the original Egyptian) calendar.

For some reason, the Indians did not make these adjustments. Surprisingly, brilliant folks like Aryabhatta and several others knew of the wobbling phenomenon but were still unable to get the calendar fixed!

Heck, we even have technical terms like Sayana and Nirayana to describe the distinction between sidereal and tropical year measurements but the sidereal calendar remains the de facto calendar for religious use

As recently as 1957, no less than a Meghnad Saha (and the government) helped fix the traditional (sidereal) Vedic calendar so that it accounted for the earth's wobble and ensured that the calendar was in actual sync with the seasons. Only problem - no one cared.

What may have been a feat of observational science 3000 years ago ended up becoming ridid orthodoxy over time.

It’s tempting to wonder why the Greeks and Egyptians fixed it and Indians did not. <opinion>Perhaps the fact that those defining calendars here didn’t exactly do stuff like agriculture and therefore didn’t have skin in the game. </opinion>

And this brings us to Pongal and Sankranthi. The term Sankranthi literally refers to the movement of the sun into a specific constellation of the zodiac, in this case - Makara (Capricorn, Mountain Goat, Lord Emperor of Insane Mountain Climbing Skillz)

And for those who care about the astronomical basis of festivals, Pongal has always been celebrated on Winter solstice - the day of the year with the longest night (and shortest day) in the northern hemisphere

So, back to our opening debate - is Jan 14 winter solstice or Jan 15 winter solstice this year? LOLJK - it’s neither

The problem with calendars not adjusting every once in a few centuries for the earth's wobble means - we celebrate Pongal in mid-January, a full 24 days after the actual winter solstice (Dec 21). In fact, 500 years from now, we will celebrate Pongal around Jan 21.

The earth will keep wobbling and our religious calendar apparently is the guy in the party who refuses to be pulled into a dance

In fact, the current difference between the Vedic calendar and the actual seasons can be used to calculate when they were both last in sync. It turns out it was 285 AD when Pongal and the actual winter solstice were in sync the last time around

So, for those who seriously believe in the astronomical significance of festivals, a 24-day belated Happy Sankranthi/Pongal/Glorious Entry of Our Lord Sun Into Mountain Goat Territory

And for the vast majority who are quite happy celebrating Pongal/Sankranthi consistently in mid-January and not worrying about solstices and wobbly earths, Happy Pongal!