Chinese New Year is observed this year on Saturday, Jan. 28.

China adopted the Gregorian calendar in 1912, but celebrations worldwide of the traditional calendar remain an important part of Chinese culture.

The beginning of the traditional Chinese calendar always falls between Jan. 21 and Feb. 20. Last year it fell on Feb. 8, next year it will be on Feb. 28.

Why the variation?

The traditional Chinese calendar is a lunisolar one, incorporating both the phase of the moon and the yearly progression of the sun through the sky (tropical year). Generally speaking, Chinese New Year falls on the second new moon (the lunar part) following the winter solstice (the solar part).

This is a pretty good rule, but it fails when a leap month is required. This last happened in 1645 and it will not happen again until 2033.

But the new moon isn’t a daylong event as the calendar hanging on your refrigerator or app on your phone might suggest. It is an event which occurs at the moment of lunar conjunction, where the Earth, Moon, and Sun form a straight line.

The January 2017 new moon occurs on Jan. 27 at 7:07 p.m. raising the question, why aren't Chinese New Year celebrations on Sunday instead of Friday this year?

Dr. Helmer Aslaksen, professor of Mathematics at the National University of Singapore had similar questions about the rules used to determine the start of the traditional Chinese calendar.

The answer lies in China’s adoption of a standard time zone based on 120ºE longitude in 1929, where the January new moon occurs at 8:07 a.m. CST Jan. 28.

The challenge with any calendar is that the 365.242188792-day tropical year (time between solstices) and the 29.530588-day synodic month (time between new moons) do not line up very well.

For this reason, calendars, traditional Chinese included, insert leap days or months periodically to reduce this drift and better align with the seasons.

Celebrations around the world welcome the year of the rooster begin the New Year’s Eve anyway, concluding 15 days later in the Lantern Festival.

The Triangle Area Chinese American Society of North Carolina plans a festival from 10:00 a.m. to 5 p.m. at Dorton Arena, with cultural performances (including lion and dragon dances), merchandise and food. Tickets are available on the organization’s website and at the door.

Coworkers tell me characteristics associated with the Year of the Rooster include “Trustworthy, with a strong sense of timekeeping and responsibility.”

Now to just keep myself from writing Monkey on all my checks.