Earth Clocks

 Title inspired by the 1988 movie Earth Girls Are Easy

A tongue in cheek assessment of timekeeping on planet Earth

by Ed Sawicki - February 2021

Our world has long-ago settled on a convoluted system of keeping time. It seems normal to us only because we grew up with it. As with many things that have evolved from concerns that have either long since been forgotten or no longer matter, we can't imagine doing it another way.

One way to see something more clearly is to imagine trying to explain it to someone who has no knowledge of it. Suppose you had to explain Earth clocks to an alien (communicating through the universal translator, of course). Our alien comes from the planet Tempor and is the female gender. You begin to explain:

24 hours

“The time it takes for the Earth to rotate once on its axis is called a day. Each day is divided into 24 hours but we express those hours in two 12-hour parts–an AM part and a PM part. There are two of each numeric hour each day—one is the AM hour and the other is the PM hour.”

She asks, “What's the purpose of the AM and PM?”

You answer, “When we first started keeping time, some of our citizens couldn't be relied on to count beyond twelve. So, we needed two 12-hour parts to get to 24.”

She asks, “Why not make your day equal to 12 hours?”

You answer, “Our historic documents don't make that clear.”

You continue, “Each hour is divided into 60 minutes. Each min...”

analog clock

She interrupts, “You said some of your citizens couldn't count above 12. How do they count to sixty?”

You answer by showing her a photo of an analog clock with hands. “They don't need to know the numbers. They look at the position of the hands.” She seems satisifed with this.

You add, “There are many other countries on Earth that ignore the 12-hour AM/PM thing and use 24-hour time. Even some people in the United States prefer 24-hour time. Some 24-hour analog clocks have only one hand similar to this one.”

24 3 6 9 12 15 18 21 >path>

Minutes and seconds

You resume, “Each hour is divided into 60 minutes. Each minute is divided into 60 seconds.”

She asks, “What if you need finer resolution than seconds? What unit divides seconds?”

“Seconds are not divided into other units. We can have fractional parts of a second.” You draw the example of 8.6 seconds on your whiteboard.

She asks, “So the .6 represents six-sixtieths of a second?”

“No, it's six-tenths of a second.”

She asks, “So your citizens are skilled at mixed number bases?”

You lie, “Yes.” realizing that you expect her to believe that citizens who can't count beyond 12 can nevertheless deal with mixed number bases.

Time zones

You continue, Time zones divide the planet into 24 zones—one for each of the 24 hours in a day. Each of these planetary zones (nominally 15 degrees of longitude wide) has a different time than all the others.”

She asks, “What's the purpose of 24 time zones?”

Thinking quickly, you answer, “So people can eat their lunch with the sun overhead.”

She asks, “What prevents your citizens from eating their lunch with the sun overhead if you didn't have these time zones?”

Again, thinking quickly, you lie, “The Culinary Luminance Laws. In our past, we had laws created that set the hours when lunch could be served. The laws assigned specific numbers on a clock to the position of our sun overhead.”

She...she...rolled her eyes!

The Year

“The time it takes for the Earth to revolve around our sun—We call our sun ‘The Sun’—is called a year. That year is divided into twelve months.

She asks, “Do the 12 months relate to the 12 hours in your half-day?”

“No, it's a coincidence. Six of the months are 31 days long. Five are 30 days long. One month, February, is 28 days long normally but 29 days long every four years. The years in which February has 29 days are called leap years. The 29th day is called a leap day.”

She looks annoyed with her universal translator and explains, “Your word leap. The meaning doesn't seem to fit.”

“It means to add.”

“Oh...What's the purpose of leap years and the variable-length February?”

“Because our ancestors weren't good at adding. The leap day is our way of compensating.”

You review the names of the months and their lengths:
January, 31 days and named for the Roman god Janus,
February, 28/29 days and named for the ancient Roman festival of purification,
March, 31 days and named after the Roman god of war,
and the other months named after gods, goddesses, Roman politicians, and ordinal numbers.

She asks, “Is it significant that months named for female gods are shorter by one day?”

You pause. “I've never been asked that question before. I don't know.”


You have to get into weeks now. Good. At least all weeks have consistent lengths. You explain that a week consists of 7 days, called weekdays and you name them, this time pointing out that weekdays are named after the Sun and planets in the Solar System.

She asks, “How do weeks relate to months? They don't divide evenly—except for February and not during leap-years.”

You take a deep breath. “They don't. Weeks and months are yearly divisions that are independent of each other.”

She accesses the calculator function on her universal translator and says, “There are 52.1428 weeks in one year, except for leap years when there are 52.2857 weeks in those years.” and looks puzzled.

“Like I said, weeks and months are two independent yearly divisions. And, it's not often that the start of a week aligns with the start of a month.”

You're trying to decide whether to get into weekdays and weekends but decide against it when you realize that there's a weekend but not a weekbegin.

Daylight Savings Time

“Because our planet is tilted on its axis with relation to the ecliptic plane, we have times of the year—called seasons—when the daylight hours shift. Our politicians have decided to shift our time ahead by one hour at a certain time of the year. At another certain time of the year, they shift it back.”

She asks, “What is the purpose of this?”

“People think that it saves daylight?”

“Where is it saved?”

“Not where. When. The time is shifted so that there's more daylight while they're awake.”

“Can't they just wake up at a time that gives them more light during the day?”

“I don't think that's occurred to them.”

Tempor time

The alien now tells you about timekeeping on her planet, Tempor. “Each rotation of Tempor—what you call a day—is divided into 1000 units called cads. Zero cad is when our capitol city faces our sun. 500 cad is when our capitol city faces opposite our sun. All of Tempor uses the same time—there are no zones.”

“Each revolution of Tempor around our sun—what you call a year—takes 401 rotations. You'd call that 401 days. We don't divide this time period into more granular units like your weeks and months”.

“We do number our rotations. We started counting a long time ago when our planet-wide government was formed. Prior to that, we had several different ways of keeping time, but none as complicated as Earth's.”

At this point, you feel a little foolish, living on a planet with a ridiculously complicated time regiment. Before she leaves, she mentions that her starchart doesn't have the name of Earth's moon and asks what it is. Now you're really going to feel silly.

Speaking of one time zone for an entire planet, here's Swatch Time:

Swatch time

In 1998, the Swiss watch company Swatch introduced Swatch Internet Time, also called .beat time. It eliminated hours and minutes, replacing them with a single number between 0 and 1000 that was called the beat. It also eliminated time zones. The concept was endorsed by Nicholas Negroponte, founder and chairman of the MIT Media Lab.

Swatch beat time
Swatch showing beat time

The Swatch company knew that their new system would be met with resistance and their watches would need to display both times for many years. They built and sold watches that displayed both traditional hours and minutes as well as beat time. The photo shows a Swatch displaying the beat time as 484. It simultaneously displays conventional time (for the local time zone) as 11:37.

Each beat represents 86.4 seconds in traditional time. The start of each day is expressed as @0 and mid-day as @500. Note the @ symbol is pronounced “at”. You might have breakfast at 350 and dinner at 750. Imagine texting your friends in faraway places, “Zoom meeting today @875” without having to specify time zones.

Beat time displayed
Linux desktops can be configured to display beat time alongside traditional time. Here, the beat time is displayed as @916.

I liked the idea and Swatch promoted it widely for a time. However, this was a step too far for most people. Although Swatch beat time disappeared in the early 2000s, there are still people who are enthusiastic over the idea. Many think that the effort stood a better chance if it were not the effort of a single company, but instead an international standards effort.

Beat time is already supported on a number of systems and languages and is simple enough to implement on systems that don't. For systems that don't directly support beat time, this C function computes it:


Click the button to see the current beat time computed by this function.


You can be anywhere on Earth when you click the button and you'd see the same beat time.

If Apple and Google put this in their phones, and their messaging and calendaring apps supported it, it would likely be a success in less than a generation. We might want to come up with a better name for it though.


Wikipedia: Swatch Internet Time

Wikipedia: Decimal time

Wikipedia: Hour

Wikipedia: Sexagesimal

Wikipedia: Nicholas Negroponte

What's in a name? Months of the year