Tag: Johannes Kepler

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.

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.