Lunar New Year kicked off Tuesday as one of the most important holidays in Vietnam, South Korea, China and other Asian countries. Typically, it starts on the second new moon after winter solstice.

On the Gregorian calendar, the civil calendar used in most countries, including the United States, the Lunar New Year changes every year, as do the dates of holidays like Rosh Hashana, Diwali and Ramadan.

It can be easy to think of a calendar as a scientific given, or a reflection of the laws of the universe. In fact, as these holidays remind us, there are as many ways to track time as there are cultures and languages. Each calendar reveals something about how the people who created it relate to the world around them while also preserving rich cultural identities and memories.

Most time-keeping traditions track the movement of the sun, moon and stars. Others consider seasonal events, like the autumnal swarming of sea worms, used to orient each year in the Trobriand Islands off New Guinea, or the flowering of immortelle trees into hundreds of tiny vermilion flames, which marks the start of the dry season in Trinidad.

Many ancient calendars, like the Chinese and Mesoamerican ones, build in fortunetelling, with prescriptions for when to build a house, get married, have a funeral and other life events. Similar calendars provide structure and comfort to people today. Britt Hart, an astrologer based in Philadelphia, said she thinks people can be drawn to horoscope-based calendars because they’re seeking a grander sense of time and order in the universe.

In the context of history, staying connected to an alternative calendar can also be a form of resisting the mainstream, or maintaining an identity outside of it. When a calendar is imposed on a society, it usually has to do with politics and power. The ability “to say when the year will start, or decide that a religious festival should be celebrated at a particular time, can be quite useful for a politician,” Dr. Stern said.

The Gregorian calendar has only been used as a global standard for about a century, and is “very much a reflection of European commerce and colonialism,” Dr. Birth said. It has now been built into computer architecture, but that doesn’t mean another calendar couldn’t one day become dominant.

A Hijri calendar from the Gregorian year 2014 hangs in Dr. Birth’s office. On it, Christmas falls on 3 Rabi al-Awwal, the third day of the third month.

He loves the reminder that, “holidays you think are stationary actually move, and those you think move are actually stationary.” It shows “how cultural these things are, rather than natural,” he said.