Why are there 24 hours in a day?
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Hey gang, what time is it? Time for Who's Smarted? Nice, but what time is it? Time for another whiff of science. That's very clever, but seriously, can you tell me the time? Just look at a clock and read out the numbers you see. Hmm, I'm hearing a bunch of different answers, including snack time and crazy dancing time.

But I'm also hearing a lot of different numbers. That's because not everybody's clock or watch is set to the exact same time. Some might be a little ahead or a little behind. Or, depending on where you are in the world, it could be a totally different time. Come to think of it, what do the numbers on a clock really mean?

Who came up with the idea of dividing a day into 24 hours? Or an hour into 60 minutes? Or a minute into 60 seconds? And what does a.m. and p.m. even mean? I guess you were right before. Who, me? It is time for another Big Whiff of Science on...

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Okay, all you listening, take another look at the nearest clock. What time is it? You probably gave a different answer than before, right? Like a minute or so later? That's because you're always traveling through time.

Think about what you're doing right now, listening to Who Smarted? The time you hit play happened in the past, and what you're hearing now is happening in the present. And the end of this episode will happen in the future. Of course, the part we just called the present is now the past. And that's basically how time works. Everything in the future eventually becomes the present, and the present is constantly becoming the past. Oh!

And throughout all of this, the clock is keeping track. But guess what? Clocks did not always exist. Huh? So how did people tell time before clocks? Any ideas? No? Well, look up. This works better if you're outside. People used to guess the time of day by looking at the movement of the sun during the day and the stars at night.

Of course, days were not divided up into hours like they are now. It was just more of a general sense of morning, midday, evening, and night. Until about 3,500 years ago, when the ancient Egyptians improved a device to tell time that's still being used today. Can you guess what that is? No? Well, let's head to ancient Egypt to find out.

Hey, Rams. Hey, Cleo. Whatcha doing? Oh, just fishing in the Nile. It's lunchtime and I'm starving. But isn't it breakfast time? Is it? Everything just kind of blends together. I'm tired of blinding my eyes, staring into the sun, trying to figure out what time it is. If only there was another way to use the sun to tell if it was breakfast time or lunchtime or crazy dancing time. Hmm.

I have an idea! I'll take this stick and ram it into the ground. Then, I'll draw a circle around the text. I'll draw some markings around the circle. Now the shadow of the stick will move along with the sun, pointing to a specific time. With that, you can figure out when it's breakfast time every day! That's amazing! What's it pointing to now?

Another whiff of science. The ancient Egyptians are believed to be the first to divide a day into equal parts using the world's oldest timekeeping device, the sundial. Sundials are still used today. You may have seen one in a garden somewhere. With the sundial, the Egyptians developed the 24-hour day. But why 24? It may seem like a random number, but there's a good reason for it.

24 divided by 2 is 12, and Egyptians cut the day into two halves, daytime and nighttime, with each side having 12 parts. At the time, 12 was an important number for the Egyptians. And can you guess why? Could it be...

B. The Egyptians used to count to 12 on one hand. Or C. Donuts come in boxes of 12, and the ancient Egyptians loved donuts. Hmm.

Got your answer? Well, there are actually more than a hundred pyramids in Egypt, and donuts weren't invented until 1847. So the answer, believe it or not, is B, that the Egyptians used to count to 12 on one hand. Huh? But how did the Egyptians count to 12 on one hand when no hand has 12 fingers? Mine does. Okay, but you're a mole. The human hand typically does not have 12 fingers. Ah.

But take a look at your hands with your palms facing you. Look at your four fingers and ignore your thumbs. See the lines made by your joints? Each of your fingers is divided up into three parts by these lines. Now count up all the parts, again ignoring your thumbs. What do you get? Twelve! Whoa! Put both hands together and you have 24! The ancient Egyptians used this counting method for all kinds of things. Ah!

So dividing up a full day into two sets of 12 parts seemed only natural to them. Those 24 parts would eventually be called hours, which comes from an ancient Greek word meaning season or part of the day. More than 2,000 years ago, the ancient Greeks also proposed the next breakthrough in timekeeping. Let's go check it out.

Claudius, you're late. Were you up all night at a toga party? No, I forgot to adjust my sundial for wintertime. Ah, it does annoy me that winter daytime hours are shorter because winter has less sunlight. Why can't hours be the same length all the time?

Good question. Maybe we can figure something out. For example, the same way you, Hipparchus, divided the globe into equal parts using lines called longitude and latitude...

What if we divided the hours of the day into equal parts? Hmm, keep talking. We need to come up with a good number that can be easily divided by lots of other numbers. Greek astronomers who have charted the night sky like the number 60 and 60 can be easily divided by 1, 2, 3, 4, 5, 6 or 10.

What if we cut up each hour into 60 smaller parts and then call them... What's a good word meaning small? Minute? Yes, yes, but let's pronounce it minute instead. Then we can divide these smaller parts into 60 even smaller parts and call them second minutes, not minutes.

Not bad. But how about instead of first minutes and second minutes, we'll just go with minutes and seconds? Much simpler that way. Brilliant as always, sir. Yes, thank you. Let's celebrate with a donut. Donuts? I don't think they've been invented yet. Mm-hmm.

Someone's really got to get on that. Even though the Greeks' proposal to standardize hours and divide them into 60 minutes and seconds revolutionized timekeeping, most people still used the varying hours for many more centuries. Then one invention changed all of that. The one whose noise is most associated with the clock. Can you guess what it is? The answer to that, right after this 60-second break.

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So you've heard how the Egyptians and Greeks used the sundial to slice up the day, creating hours, minutes, and seconds. There's an itty-bitty problem with the sundial. Can you think of what it is? Yep, it needs the sun to work, to tell time on cloudy, rainy days or at night. Ancient civilizations invented timepieces that used candles, oils, or water.

They weren't very precise, and for hundreds of years, hours still varied in length, as minutes and seconds were too hard to measure. The first mechanical clocks, which introduced that famous tick-tock sound, were developed in the 1300s. With gears, weights, and springs, these clocks created a precise measurement of time, with every hour measuring the same length. Over the next few centuries, mechanical clocks would start displaying minutes and seconds.

Today, your alarm clock, microwave, cable box, and smartphone tracks time electronically, sometimes with help from the internet. These clocks show a digital number with the hour and minute, and sometimes two letters, AM or PM. So what do those letters mean? Awesome minutes! Power moons. Nope. AM and PM have to do with midday, the point in time when the sun is directly overhead and when there's no shadow on the sundial.

The middle of 24 is 12, so that's why midday is at 12 o'clock or noon. A.M. and P.M. are abbreviations of words in Latin, the language of the ancient Romans, from a region that is now called Italy.

A.M. stands for the Latin words antimeridian, which means before midday, which is why the morning hours use A.M. P.M. stands for postmeridian, which means after midday, which is why afternoon and evening hours are labeled P.M. P.M.

While many English-speaking countries use a.m. and p.m., much of the rest of the world relies on the 24-hour clock. So in those places, 1 p.m. would actually be hour 13. And times like 3.30 p.m. and 9.45 p.m. are 15.30 and 21.45. ♪

The 24-hour clock is also called military time because it was adopted by military forces to avoid any confusion between a.m. and p.m. times during battles, attack planning, or even boot camp.

Cadets, I want you all to drop and give me 50 push-ups. But sir, you said push-up time is at 7. My watch says 7 now. But sir, your watch is a 12-hour clock, and we go by military time. That means, after noon, you have to add 12 to the hours on your watch, and say 100 when you mean zero minutes. So, if it's 7 p.m., it's 1,900 hours by military time.

Sir! 1900 hours? What are we supposed to do at 1900 hours? I have the schedule, sir. Well, it says here, uh... Speak, cadet! What time is it? It's crazy dancing time! Oh well, looks like it's time for all you listeners to join in on the dancing. I join in too, but I need to read the credits. An out-of-this-world shout-out to Zohara in the Blue Mountains, NSW, Australia.

I hear you listen to Who Smarted every day and still want more. Now that's what I call dedication. We love having you smart with us, smarty pants. This episode Time was written by Dave Beaudry and voiced by Katie Lou Chastain, Sheffield Chastain, Brandon Bayliss, Adam Tex-Davis, Charlotte Cohn, Jason Williams, and Jerry Kolber. Technical direction and sound design by Josh Hahn.

Who Smarted? is recorded and mixed at the Relic Room Studios, and our associate producer is Max Kamaski. The theme song is by Brian Suarez. Lyrics are written and performed by Adam Tex-Davis. Who Smarted? was created and produced by Adam Tex-Davis and Jerry Colbert. This is an Atomic Entertainment production. Who Smarted?