As 2023 becomes 2024, time is briefly on our collective minds.
To astronomers, time is a fundamental quality woven into the fabric of the universe, so much so that they refer to space as spacetime.
Time in the abstract significantly differs from our ways of quantifying its passage, an inconvenient kluge cobbled together over millennia.
The year, for example, is determined by a single orbit of the Earth around the sun, about 365.25 days.
The “moonth,” or “month,” as you Earthlings call it, was initially measured by the moon’s orbit around Earth. A set of lunar phases, the ancient way of determining a month, takes about 29.5305882 days. The trouble comes because 29.5305882 doesn’t divide evenly into the 365.25-day year.
We simply can’t have months of equal days. Furthermore, what do we do with that pesky .25 day when we measure a calendar year?
Moreover, Earth’s orbit is seamless. We’ll find no convenient tick mark to tell us when the new year begins. So why do we start in the middle of the blessed winter?
The logical time to initiate the calendar year is the first day of spring — when the world comes alive again after its winter dormancy. The ancient Romans, from whom we inherit our current calendar, started the year in March.
The Roman calendar was only 355 days long, i.e., 12 months of, on average, 29.58 days each — pretty close if all you care about is the length of the month. Unfortunately, that left the problem of that 365.25-day solar year.
The priest-astronomers in charge of the calendar occasionally added an extra month after Feb. 23. However, they often did so for purely political reasons. If some favored bureaucrat wanted to lengthen his term in office, the priests added a month.
By 46 BCE, the calendar year was a couple of months out of sync with the solar year. Their March happened during our modern January.
Astronomers advised Julius Caesar, the Roman dictator at the time, to add 67 days to November that year, essentially stopping the motion of the calendar for two months. Voilà! The year began in January, but at least spring began in March again.
To reduce future difficulties, Julius set the year at 365.25 days, adding a leap day every four years. But there was another problem. The solar year is actually 365.242199 days. Julius’s year was 11 minutes and 14 seconds too long.
The extra 11 minutes may seem trivial, but they added up over the centuries. By 1582, spring’s first day was 10 days removed from the traditional date of March 21.
So Pope Gregory XIII decreed that years beginning centuries, like 1900, would not be leap years. Exceptions would be made for years divisible by 400. Consequently, the year 2000 was a leap year.
Additionally, Gregory removed 10 days from October 1582 to synchronize the calendar with the seasons. The pronouncement caused considerable consternation, especially among folks who had to pay an entire month’s rent for an October that lasted only 21 days.
Even your clocks are wrong when measured against the astronomical motions they are based on. Local noon is supposed to happen when the sun reaches its highest point. But the sun reaches its highest point at different times for every location measured from east to west on the planet.
We can’t have all our clocks measuring different times. We thus invented time zones to even out the differences a bit.
However, if you are on the eastern edge of a time zone, astronomical noon is at 12 p.m. If you live in central Ohio, noon happens at about 12:35 p.m. because we are about halfway into the time zone.
And then there’s that weird governmental intrusion called Daylight Saving Time. For most of the year, noon here is at 1:35 p.m.
The clock and calendar are constant reminders that we live on a rotating planet revolving around a star. Our measurement problems happened because Earth doesn’t take an even number of days to orbit the sun, and the moon takes an uneven number of days to orbit the Earth.
Here’s something to think about as the ball drops Sunday night. Our time-measuring methods are necessary fictions, imperfect human inventions.
Tom Burns is the former director of the Perkins Observatory in Delaware.
