Time is a strange dimension. Mathematically we can move all around in space, but with time all we can do is follow along as time keeps moving “forward”. We can look back in time through memory, history and scientific methods, but when we go forward we have to make predictions. These can be as good as predicting a solar eclipse years in advance. Or as poor as guessing who's going to be president next year.
While time is real (possibly an effect of the increase in entropy) our measurement of time is a human construct. But we do use some regular cycles to make things fit with the real world. Like we use years as one of our units which is based on the time it takes for the Earth to go around the Sun. And a day is the time it takes for the Earth to turn on its axis. While a month is measured by the phases of the moon. And for millennia people have put all these measurements together into calendars.
One common way of doing this is to use a lunisolar calendar. Months are defined by the moon, with a certain number of days in a month and a certain number of months in a year. And using positions of the sun and phases of the moon, important days are determined. And we have a couple important days coming up.
Chinese New Year is going to be February 8th (New Year's Eve is the 7th). This is the day of the new moon midway between Winter Solstice and Spring Equinox. So that's a combination of solar and lunar events.
As is Easter. Easter is determined by the Sunday following the first full moon after the Spring Equinox. And that determines several dates before it. Including one on the 9th. Mardi Gras which is a foodie holiday if there ever was one. (I'm planning to make beignets this year.)
But things start breaking down since a year isn't a fixed number of days. It is actually 365.37 days long. And the phases of the moon complete in 29.53 days. So over time, without taking some kind of corrective action, calendar months will get out of sync. Some calendars (for example the Hebrew calendar) can in an extra “month” according to a schedule. The Chinese calendar uses a different method for keeping things in sync.
The Gregorian calendar, which is the one we use, has fixed months of varying lengths with one more day added every four years (well, approximately, but it's going to be some time before a year doesn't fit that rule). And this year we get that extra day. February 29th is coming up.
And while time itself doesn't care what method we use to measure it, I think we should all plan on putting that “extra day” to good use. Too bad it's a Monday.