Happy New Year 404 ME

As the common era carried across the world by European colonialism contracts to its core, everyone is again aware of multiple celebrations of new years. In India different regions have slightly different ways of counting the year, so there are many Indian new years, but there are two major groups: one in the middle of April, another about a month earlier. These traditions are actually wider, being celebrated across much of south and south-east Asia. The Chinese new year falls between the last weeks of January and February. Korea, Vietnam and Tibet have customs similar to this. Parsis and Iranians celebrate the new year on the day of the spring equinox. Several African cultures have a new year during the summer of the northern hemisphere. And there are a whole set of cultures who celebrate new year in autumn. So is the year just a human social construct?

You could treat it as such, but it is also true that the earth has cycles which are independent of humans. The succession of day and night, the slower waxing and the waning of the moon, the even more stately tilting of the axis of rotation which produces seasons, they are all cyclic astronomical phenomena. We base the day on the first, the month on the second, and the year on the third. What we see as the tilting of the earth’s axis is actually due to its pointing in a (more or less) constant direction in space as it takes us on its grand circuit around the sun. So the year is a measure of the time the earth takes to go around the sun. You may think of different cultures of new year as different ways of marking a special point on the earth’s orbit around the sun.

But 404 years ago Kepler opened a way to showing us that one point is really special. He found that the earth’s orbit around the sun is an ellipse, and not a circle as many cultures had concluded. He also discovered that on the day when the earth passes closest to the sun, it is travelling fastest on its orbit. This is the point which the earth reaches today, every January 4. I guess that makes it the true astronomical new year. Today we enter the new year 404 Modern Era.

A happy new year to you.

The one true new year!

Niece Mbili sent The Clan a New Year’s greeting card which shows two aliens puzzled about why humans celebrated yet another turn of their planet around the sun. That’s exactly what a year is: one complete orbit around the sun. The year begins each time you reach a fixed point on the orbit. Which point? Aye, there’s the rub. All calendars in use are too ancient to have made an informed choice.

But not the one true calendar (“One of the two true calendars”, Simplicio interjects). Since the orbit of the earth is an ellipse, and not a circle, there are two points on the orbit which are special: the point at which it is closest to the sun (perihelion), and the one at which it is furthest away (aphelion). The earth comes closest to the sun some time today: January 4. That’s pretty close to what you may have been celebrating, so remember to make that little correction next time (“Easily solved,” Sagredo chides Simplicio). And this naturally gives us a second holiday: mid year on July 4, when the sun is furthest from us.

Another magic of this new year is that it occurs at the same instant around the globe: whether you are in Mumbai or Mombasa, in Madrid or Manitoba or Manila, in Melbourne or Motsomi or atop Monte Darwin. When the earth comes closest to the sun has nothing to do with where on earth you are. So I’m planning a wild New Year’s party at just after noon today. You can check the local time of your party in this calculator, but it will be at the same instant as mine.

Now you might ask whether there is a special meridian on earth, one where the party happens at midnight every year. Very strangely, the answer is no. The length of the day and the length of the year have (almost) nothing to do with each other. As you know, a day is the time that the earth takes to spin around itself once, the year the time to spin around the sun. The word “almost” is important: the year being an exact multiple of the day is forbidden by an interesting piece of physics: resonance. The story seems to be that when two times (such as the day and year, or the month and year) become multiples of each other, the orbits become unstable. So in a solar system which has lasted for billions of such orbits, you’ll never find these “resonances”. It’s an amazing piece of physics, discovered only about seventy years ago (at the height of the cold war) by the Russian physicist Andrey Kolmogorov.

All that for the time of the new year. Now the counting of the year zero. Since the definition of the new year’s celebration depends on the shape of the earth’s orbit, one has to have a special place in the calendar for the date of the discovery of this shape. Johannes Kepler published this discovery 403 years ago. So that’s why the new year, 403 Modern Era, starts today.

A very happy new year to you.

Unfortunately, the universe is also a little more complicated than the pretty picture which gives us calendars. Einstein would have us know that this is all approximate, and that when you try to pin down the time of the new year’s party to an accuracy of a few parts per hundred thousand, the whole idea of a new year, indeed of a cyclic calendar, becomes meaningless. Lucky for us that our senses do not have that accuracy, and we can live generations with the lie called a year.

Year 402, modern era

The eerily empty Park Street in Kolkata heralded the imminent end of the year 401 of the modern era. Usually this street is crowded with party goers in the evenings of the ten days between Newtonmas and Perihelion day. Not this year. We ducked into an old favourite of a coffee shop, nearly a hundred years old now, but still filled with young people. This year the wait for a table was only two minutes, not two hours. The Family’s face was glowing, she’d heard a lot about the street at this time of the year, and she was happy to be there.

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The long nights of this season seem to be made for fairy lights, and in this pandemic year people have put a little extra into them. We decided to come home for the new year. The new year? There are so many different calendars in India, that the arbitrariness of choosing a date to begin a year is obvious. Is there really a special date to celebrate as we roll along around our star? It turns out that there are two such dates: one when we are closest to the sun (perihelion), and another when we are furthest (aphelion). If we want to choose something close to the new year in the common calendar, then Perihelion day, January 4, today, it must be. A different new year’s day deserves a different era to go with it. In the 16th century of the common era, Nicolaus Copernicus first realized that the earth goes around the sun. And then, in the early years of the next century, Johannes Kepler realized that the path of the earth was not a circle, but an ellipse. It is because of the ellipticity that there are special points in the orbit, a perihelion and an aphelion. So this discovery should mark the beginning of the modern era of a rational calendar.

Welcome to the year 402 of the modern era. The last of Kepler’s laws was published that many years ago. The start of the fifth century was traumatic for many, filled with losses. I seem to have spent mine in the safety of my kitchen, judging from my favourite photos of the year. But this is a new year, with new hopes of accommodating this virus without harm to ourselves through a vaccine. This is a year to celebrate careful study of the world around us, and to act on this understanding for the preservation of our place in the world around us. So a happy new year, 402 ME. ☀

The way of the world

That the earth’s axis is tilted around the plane of its orbit was known even to ancient civilizations who had no understanding that the earth moves around the sun. After all, the noontime sun moves polewards in summer and in the opposite direction in winter. As a result, days are longer in summer, and nights longer in winter. Even a layman could see that. It was also fairly easy in the temperate zones of the earth to connect these motions to four distinct seasons. This was the beginning of ancient astronomy, and its off-shoot, which is the modern calendar.

Doubt thou the stars are fire,
Doubt that the sun doth move,
Doubt truth to be a liar,
But never doubt I love.

Hamlet (Act 2, Sc 2) William Shakespeare

But today, as the world begins another mad celebration of the arbitrariness of this calendar, and the decimal system of writing numbers (the end of the year, and, mistakenly, the end of the decade), I was moved to ask whether any special meaning could be given to a calendar. In the Elizabethan era, even as Shakespeare was writing about the fixed nature of the earth as an eternal truth, the earth was displaced from the center of the cosmos. It was realized that the earth orbits the sun, and that the sun was but one out of many stars. It was realized that the earth moves in an elliptical orbit around the sun. The difference between the long radius and the short is just about 1 percent of the radius, so this difference is not easily observed.

It remains that from the same principles we demonstrate the form of the system of the world.

Principia Mathematica (Book 3) Isaac Newton

Small it may be, but the ellipticity is there, to mark special points on the orbit: special dates of the year. There is a date when the earth is furthest from the sun, and one when it is the closest. Between January 3 and 4 the earth comes closest to the sun. I will mark the beginning of a new orbit around the sun, a new year, on the coming Friday. How great a coincidence it is that this will come 12 days after the birthday of Isaac Newton, the man who understood that the reason for a ripe apple falling from a tree is the same as that which forces the orbit of the earth to be an ellipse. And what is special about the coming year is that it ends the 4th century after Johannes Kepler’s discovery (by 1619 CE) of the laws of planetary motion; that’s not the end of a decade, it is the end of the century. 2020 CE may as well be called 401 Keplerian Era.