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.