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.