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. Let's explain Earth's timekeeping 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 doesn't seem satisifed with this answer.

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 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.


You have to get into weeks now. Good. At least all weeks have consistent lengths. You explain that a week consists of 7 days, and you name them, this time pointing out that they're 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 some amount at a certain time of the year. At another certain time of the year, they shift it back. Many places on Earth use different amounts of time for the shift.”

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 and revolutions. 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.”

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.


Wikipedia: Decimal time

Wikipedia: Hour

Wikipedia: Sexagesimal

What's in a name? Months of the year