Winter

For those who are familiar with the history - or, simply, have read De Vinci Code of Dan Brown - you may know that Christmas was not the original birthday of Jesus. The catholic church adopt the date of Winter Festival of the Roman Empire to celebrate the birth of their god.

And, it is commonly quoted that on this very date, the length of the day was shortest in the northern hemisphere.

But, hold on, doesn't the Chinese say that it is the date of Winter Solstice (冬至) - which is almost always 22nd December - that has the longest night ?

Em ... they are both right, to a certain degree.

You know what, there is a whole week in December each year that has an almost equally short days in the northern hemisphere. They are, generally, from 19th to 25th December.

In other words, the Chinese Winter Solstice is in the middle of this very period, and exactly the time when the Earth's axial tilt is farthest away from the sun.

How about Christmas? It is the end of this period of short day; ancient Romans took it as the day that the Sun reversed its southward retreat and proved itself to be "unconquered".

And, by the way, neither of these dates has the latest sunrise or earliest sunset. The former took place in mid-January, while the latter late November - each around three weeks from the Chinese Winter Solstice.

Merry Christmas.