Does Anybody Really Know What Time It Is?

By Mark Dahmke

This paper was presented at the Tom Carroll Lincoln Torch Club, September 15, 2025.

I decided to revisit my very first Torch Club paper, presented in March, 1987. The first paper came about because of an editorial in the Lincoln Star by Bill Dobler, advocating in favor of permanent daylight saving time. This brought a reply from a reader who preferred that we stay on “God’s Time.”

That triggered a reply from me, pointing out that even on standard time the reader is not on “God’s Time” because time zones were established by man in the 1880s as a way of simplifying the coordination of railroad schedules. I have since learned that this is not entirely accurate.

Dobler replied, noting my comment about God’s time being defined only by sunrise and sunset, but pointed out that the reader could have been right about God giving us Time, but wrong about which time He gave us. “The story of creation just didn’t go into that much detail,” Dobler wrote, and went on to say that what he liked about God’s Time was that it seemed to be less demanding than man’s. “His only measure of time was a lifetime and we remain uncertain as to when that starts and mercifully in the dark as to when it might end.”

Back to the reader’s letter: she complained that daylight saving time was confusing. “I can’t understand why man has to try to improve and change things he has no business messing with. Why can’t the people who like it so much just get up an hour earlier and let those of us who don’t like it get up with the standard time?” and “I feel God did a good job – why do people have to mess it up?”

If she really wanted to be on “God’s Time” she would need to use local apparent time. The easiest way to measure one solar day is to measure the position of the Sun at local apparent noon or high noon on two consecutive days. But since the Earth’s orbit is slightly elliptical, an apparent solar day can be 20 seconds shorter or 30 seconds longer than a mean solar day. Long or short days occur in succession, so the difference builds up until mean time is ahead of apparent time by about 14 minutes near February 6th, and behind apparent time by about 16 minutes near November 3rd. The equation of time is this difference.

The real problem is that for most of history the rotation of the Earth was our clock, but it only tells time in units of one solar day. When we needed greater precision, we had to find ways to break it down into hours and then minutes and seconds. When we had the ability to precisely measure seconds we ran into a big problem– the Earth is not an accurate clock. The length of the day varies for a variety of reasons that I’ll get into later. Much of this paper is about the work-arounds we use to live on a clock that doesn’t keep time very well, and the work-arounds we employ to live on a spinning globe.

The rotation of the Earth defines the length of a day, but is there a more consistent and accurate way of determining the length of a day? The stars are so far away from us that their position appears to be constant for very long periods of time. What if we measure the day by observing the position of a bright star? The time it takes for a star to return to the exact position it held the previous night is called the Sidereal day and is 1436.09 minutes long.

 

This diagram shows the movement of the earth around the sun. Each day, it moves about one degree in its orbit. The stars, seen at midnight on successive nights will appear to shift westward as the Earth moves counterclockwise in its orbit. A star will arrive at the same location three minutes and 56 seconds earlier each night.

We can just as easily measure the time it takes for the Moon to return to the same position in the sky. This way of measuring time is extremely useful when it comes to predicting high and low tides. The lunar day is 1490 minutes long because the Moon drifts eastward against the stellar background thirteen times faster than the sun does, completing an orbit in only 29 and 1/2 days. With respect to the stars, we have to wait an additional 54 minutes each night for the moon to pass overhead again. Lunar time isn’t good for much, other than keeping track of tides because it rapidly gets out of step with solar time.

Source: Wikipedia. Author: James O’Donoghue. Creative Commons Attribution 3.0 Unported license.

Originally, the length of the hour, minute and second were defined as fractions of the tropical year, but in modern times, precise measurements have shown that the rate of rotation of the Earth and the length of the year change gradually for various reasons. The tidal drag of the Moon is slowing the rotation of the Earth, and changes in the Earth’s magnetic field and in the liquid core of the planet cause it to speed up and slow down in unpredictable ways.

To solve this problem, one second is now defined by the oscillations of the Cesium 133 atom, instead of being one 86,400th of a solar day. This is known as atomic time. Because the length of a second is now decoupled from the rotation of the Earth, we occasionally have to add or drop leap seconds to keep atomic clocks in sync with the solar day. More about that later.

Assuming that we use solar time as the basis for dividing the day into parts, we have to contend with the variations of the earth’s orbit, its axial tilt, and other factors. As I mentioned earlier this is the equation of time. What is shown here represents the gain and loss from the Earth’s elliptical orbit, but there are other factors that also require small adjustments.

This image shows the position of the Sun at Noon – Standard time in the winter and Daylight Saving time in the summer. Because of the combined effects of the equation of time and daylight saving time, on July first the Sun isn’t directly south until 1:30pm central daylight time.

Prior to the industrial revolution, the system of local apparent time served us well since the average speed at which you could move from place to place was about 4 miles per hour. With the invention of the steam engine and railroads, it suddenly became possible to cover vast distances in a matter of hours, and more importantly, it could be done on a fairly reliable schedule.

Source: Stellarium. Composite image by Mark Dahmke.

Suppose you board a train in Lincoln at 12:30 PM Local Apparent Time. This is based on the position of the sun at local apparent noon in downtown Lincoln. You travel to Omaha at a speed of 25 mph and arrive at 2:07 PM according to your pocket watch. The longitude of downtown Lincoln is 96 degrees, 42 minutes West and Union Station in Omaha is 47 minutes of Longitude east of Lincoln. Each degree of longitude corresponds to 4 minutes of time, so the time of local apparent noon in Omaha is 3 minutes, 8 seconds earlier than it was in Lincoln. When you arrive in Omaha, it will be 2:03:52 pm local time. If we consider a trip from Omaha to Des Moines, the difference increases to 9 minutes and 40 seconds, or enough to cause serious scheduling problems.

Credit: Mark Dahmke

Timekeeping on North American railroads in the 19th century was complex. Each railroad used its own standard time, usually based on the local time of its headquarters or most important terminus, and the railroad’s train schedules were published using its own time. Some junctions served by several railroads had a clock for each railroad, each showing a different time. Because of this a number of accidents occurred when trains from different companies using the same tracks mistimed their passings. [Source: wikipedia]

Several attempts were made to standardize, but none were universally accepted by the railroads. Finally the Chief Meteorologist at the US Weather Bureau divided the US into four zones for consistency among weather stations and in 1883 convinced the railroads to adopt the same time zone system.

Source: https://chicagology.com/transportation/timeconvention/

Naturally there were those who did not appreciate the change.

On November 23, 1883, the Sidney Journal reported: “We will turn the clock back just 28 minutes. And what will become of the 28 minutes? That will be lost, dropped out of existence as though it had never been. We will be 28 minutes younger than we were.” The Cleveland Evening Post states: “Radical changes, no matter how reformatory, which break up old customs, almost sacred because of their antiquity, are never submitted to without grumbling.”

Not long after the introduction of standard time, long distance telephone service became available between New York and Chicago, extending to Denver by 1911. Later still, radio and television programs and news broadcasts had to be recorded and timeshifted to accommodate east and west coast prime time reception.

Daylight saving time was first enacted in the US in 1918 in the interests of adding more daylight hours to conserve energy, and was implemented again during World War II. It was never popular with farmers who actively lobbied against it due to its impact on farming. Every few years another bill is introduced to switch us to permanent daylight saving time or permanent standard time, but in my view that doesn’t really address the larger issue. Also, technology has changed dramatically in the past forty years as has our need for much more precise timekeeping and coordination.

Time shifting in the jet age becomes complex when you fly across the international date line, sometimes arriving before you left, based of course on what clock you’re looking at. Ever since there have been time zones there have been people complaining about living near a boundary line. Especially if your city happens to be on the boundary.

This is one of my favorite xkcd cartoons. It’s the edge cases that cause most of the angst. In this case Emily was born exactly at the north pole, in every time zone at once, on February 29th and the airline was in the process of changing ownership between countries.

For convenience and political reasons, time zone boundaries have taken some unusual twists and turns over the past century. I would even go so far as to say that time zones are now as politically charged as language and cultural identity.

In my 1987 paper, I offered a possible solution. Arthur C. Clarke once suggested that we could switch to four six hour continental time zones. However looking at the current map and noting where some of the lines are drawn, it’s probably best to just do away with the idea of trying to make nice orderly one hour zones and let each country do its own thing. China is geographically wide enough to span five zones but the entire country follows Beijing Time or zone 8. Malaysia is spread across two time zones but the entire country also uses zone 8. Cambodia, Thailand and Vietnam are directly between China and Malaysia but chose zone 7.

Credit: XKCD. This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License.    https://xkcd.com/2549/

The international date line and associated time zones are a confusing mess. Samoa and American Samoa are just 50 miles apart but are a full day apart because of the international date line.

The nautical date line, which is not the same as the IDL, is a de jure construction determined by international agreement. It is the result of the 1917 Anglo-French Conference on Time-keeping at Sea, which recommended that all ships, both military and civilian, adopt hourly standard time zones on the high seas. The United States adopted its recommendation for U.S. military and merchant marine ships in 1920. This date line is implied but not explicitly drawn on time zone maps. It follows the 180° meridian except where it is interrupted by territorial waters adjacent to land. In theory, ships are supposed to adopt the standard time of a country if they are within its territorial waters, then revert to international time zones as soon as they leave. In practice, ships use these time zones only for radio communication and official purposes. For ship-board purposes, such as work and meal hours, they use a time zone of their own choosing. [Source: Wikipedia]

Since the initial concept of nice orderly 15 degree longitudinal zones has been thrown out the window due to geographic and political boundaries, and since we now use GPS and computers to navigate and tell time, I think the more feasible option would be to adopt “my time” or “circadian time” which means we all have multiple clocks: one synced to our circadian rhythm, another for official local time and one for Universal time. Your clocks and Internet-connected devices can keep track of the time zones for you.

In the Internet era, the world effectively runs on Universal Time. The actual standard is called Coordinated Universal Time or UTC and is within one second of Mean Solar Time at 0 degrees longitude, or in other words, Greenwich Mean Time.

If you work the night shift, you could set your watch so that your Noon is 2am standard time, or if you’re an airline pilot, your watch would display your circadian time and Universal time, which is the time used for everything aviation-related. Modern smartwatches can monitor your pulse and blood pressure, so why not let a smartwatch monitor your vitals and determine your optimal circadian time? It can also easily convert back and forth to local time and can assist with scheduling appointments with others who are operating on their own circadian time.

Timekeeping in computers is done by incrementing a counter every millisecond (or in some cases every microsecond). In most computers, the current time is represented as the number of non-leap seconds since January 1st, 1970. This is known as Epoch Time or Unix Time, since most computers and the majority of timekeeping servers run a variant of the Unix operating system.

Unix time differs from Coordinated Universal Time and International Atomic Time in its handling of leap seconds. While UTC includes leap seconds to adjust for discrepancies between atomic time and solar time, Unix time does not. [source: Wikipedia]

When your computer, phone or smart watch displays the time, it’s retrieving the UTC value in seconds since 1970 and converting it to your local time, taking into account your time zone and any leap seconds that have been applied. It also knows when to apply daylight saving time based on your current location.

There is a critical software component that we all depend on, that is used in virtually all computers, Internet-connected appliances and millions of other devices. It’s called the Network Time Protocol. There’s a module that runs either as a client or as a server in all of these devices and many other places you would not suspect.

An oversimplified description of NTP is that it’s designed to mitigate the effects of delays over networks such as the Internet, where the transit time of data varies with distance.

In the old days keeping clocks to within a few seconds was good enough, but now world markets depend on much greater accuracy. Almost every computer has a real time clock, but all clocks drift slightly and get out of sync. NTP provides a way for all the billions of clocks in the world to stay in sync with each other. NTP was designed in the early 1980s and can achieve better than one millisecond accuracy under ideal conditions. On a global scale NTP can maintain accuracy in the range of tens of milliseconds.

Image Credit: Mark Dahmke

The Precision Time Protocol or PTP was created in 2002 to solve a problem: the older NTP was no longer accurate enough. PTP enables sub-microsecond accuracy, and even billionth of a second accuracy, which is suitable for measurement and control systems, financial transactions and networks that require precise timing.

Today, it’s used in places where even the tiniest difference in timing can have a huge impact, such as mobile networks and stock trading systems. Both NTP and PTP have the ability to compensate for speed of light delays and transmission latency across global Internet connections.

Fiber optic cables are preferred over satellite links which can have significant speed of light delays. But even fiber connections have speed of light delays and other latency issues that can make timekeeping difficult, even over short distances. However, a signal transmitted out to a geostationary satellite and relayed back to a ground station on another continent has a much worse minimum delay of 270 milliseconds.

We now have in place the infrastructure to manage timekeeping on a global scale and take into account the delays associated with speed of light and network latency. How do we extend those services to other planets? NASA has been directed to establish a lunar time zone to aid in coordinating international missions to the Moon and future lunar bases.

This is more complicated than it sounds because due to the theory of relativity, time passes at a different rate on the surface of the Moon and on other planets. While the difference is very small, it can’t be ignored.

You might have heard that time slows down near a black hole due to its extremely strong gravitational field. An observer far away from the black hole will see events near the black hole happen at a slower rate than an observer near the black hole.

This holds true for any gravitational field, not just black holes. A mountain climber with an extremely accurate clock would notice that time is passing slightly faster at the top of Mt Everest than at sea level.

The takeaway for this slide is that time is passing at a different rate for each marked location. This would have been an astonishing concept to anyone living before Einstein published his theory of special relativity.

Image credit: Mark Dahmke. Earth Moon and Mars images credit NASA.

This chart shows cis-lunar space – the area including the Earth-moon system and nearby Lagrange points. The Lagrange points are locations where the gravitational influence between the Earth and Moon is at equilibrium. Using L1 between Earth and Moon as a reference point, as you move closer to either the earth or the moon, time passes more slowly. Since gravity at the surface of the moon is lower than at the surface of the earth, time passes at a slightly faster rate, on the order of 58.7 microseconds per day. This sounds like a small number that can be ignored, but it accumulates. Over 50 years the difference is about one second. Any atomic clock placed there will gain time relative to an earth-bound clock. The same holds true for Mars but clocks on Mars will diverge at a different rate because gravity there is stronger than on the Moon.

If it’s just Earth and Moon, one could probably ignore the problem by introducing a leap second periodically to keep the clocks in sync, but this still doesn’t address the real problem. Humans could compensate for it but computers operating at speeds where a millionth of a second is a long time, must take it into account.

Image source: NASA

Now we’ve established the need for taking into account time dilation, but we’ve neglected the other side of the original time zone problem. On the Moon, it’s pretty easy to solve, since the lunar day is the same as its period of rotation around the Earth. There’s no need to divide up the moon into separate one hour time zones because no one who lives on the Moon is going to tell time that way. The sensible thing to do is pick a time zone that synchronizes with Earth-based ground control or use UTC. The Apollo missions operated on Central Time because the control center was in Houston. The lunar time servers will still have to keep track of the time dilation effects.

Mars presents a different set of problems. The solar day on Mars (also called a “Sol” to distinguish it from a day on Earth) is 39 minutes longer.

For the Mars Exploration Rovers and other missions, the operations teams at JPL worked on “Mars time,” with a work schedule synchronized to local time at the landing site on Mars. They wore wristwatches calibrated in Martian time. This resulted in the crew’s work schedule shifting approximately 40 minutes later each day.

Image credit: Mark Dahmke. Mars image credit: NASA.

The beauty and longevity of our current system of timekeeping is that it is based on the numbers 12 and 60. 60 is the smallest number divisible by the first six counting numbers and by 10,12,15, 20 and 30. 24 is divisible by 3, 6 and 12. This was all perfected by the Babylonians who borrowed it from the Sumerians who invented it in the 3rd millenium BC.

If future residents of Mars decide to keep the 24 hour day and 60 minute hour, then the length of one second would have to change. One possibility would be to switch to decimal time. China used decimal time alongside duodecimal time throughout most of its history. It was used until 1645 when a new calendar based on European astronomy was brought to China by the Jesuits. France attempted to switch to decimal time several times but it never caught on. The 24 hour day has become so ingrained in our culture that, like the author of the letter to the newspaper, it seems like it was created by God, and its unlikely to ever be changed, at least on Earth. Mars residents might decide to switch to decimal time just to make a break with the home planet, and it might be easier to change the nomenclature to avoid confusing Earth time with Mars time.

In 1998 the Swiss watch company Swatch introduced a line of digital watches that divided the day into 1000 “beats” each being 86.4 seconds long. One centibeat is 0.864 Earth seconds. A centibeat on Mars would be .887 seconds which would be close enough to one Earth second so that mentally converting between seconds and centibeats wouldn’t be much harder than remembering that one yard is about equivalent to one meter. Mars will also need its own time zones and its own atomic clocks. But the planet will always be out of sync with Earth because of the length of its day and its surface gravity time dilation, and will always be anywhere from 5 to 21 minutes out of sync because of the speed of light communications delay.

So does anybody really know what time it is? Before railroads, computers and space travel, timekeeping was relatively simple. But eventually, time zones had to be added to accommodate our need for speed. The theory of relativity was the final nail in the coffin for a deterministic clockwork universe, when Einstein showed us that there is no standard clock for the universe. Different observers disagree on which events happen at the same time.  Although time’s arrow seems like a fundamental property of our universe, it’s likely that it’s just an emergent property.

Our awareness of the passage of time is related to our perception of our environment. The Earth spins on its axis, so we count the days and years. We experience a one-way flow of time because we and the world we perceive are made up of countless chemical and physical processes that are inherently irreversible.  So the time we’re measuring is not a fundamental property of the universe, but merely an illusion — a measure of change. We create clocks and time zones so that everyone’s illusion of time stays aligned, so our society can function.