Hey everyone, thanks for tuning in to dnews plus again today I am trace, and this is our series on how we keep time or also why we keep time. This way we’re talking about the calendar, so we’re gonna talk about what a day is how we got to a week why there are 12 months in the year and even what a year really is, because you probably Have some idea, but trust me there’s, a lot more to it than you think, but first let’s start with the day here’s, a fact that you probably all know there are 24 hours in a day Right we’ve all learned that, and that is the amount of time it takes for the earth to rotate on its axis one time easy, but that statements not actually that true, it’s only kind of true and to understand it.
You have to back up a bit so the Earth spins on its axis in a counterclockwise direction, and it does so because of how the Earth’s formed. We’ve done this before. Maybe you remember from our formation series.
4.6 billion years ago, the solar system formed. It was a huge cloud of gas and dust and it collapsed under its own gravity and started to spin toward the center of the solar system faster and faster in formed, planets and flattened out into a disk.
And in all of these things, some of those I said out of order, but they were all there and these new formations inherited the spin from that rotating cloud of gas and dust that the formation of the solar system.
So how long does it take for the earth to rotate once if you said 24 hours, you’re close, but by Price is Right rules you are out because it’s, only 23 hours and 56 minutes, and you went over my Friend, this is the true measurement of rotation.
It’s called a sidereal day and the sidereal is from the Latin word, sidereus, meaning star. You know etymology, you guys love it. I love it. This is because it’s. A measure of the Earth’s. Rotation based on the star takes 23 hours and 56 minutes for a specific star to show back up in its exact position in the night sky again, so it’s, not 24 hours, but it’s.
Close many astronomers use. The first point of Aries the reason they use. That point is because that’s, where the celestial equator and the celestial Meridian intersect. It’s, similar to how the earth has an equator and then a Meridian that divides a to the hemispheres of you, know: east and west, north and south.
They have that also in the sky. That’s. Basically, the zero point of the celestial sphere: that’s around the earth. It’s imaginary, but you got to pick. You know point somewhere so why isn’t the day 23 hours and 56 minutes long, because, even though all of that makes sense in a celestial sphere, we don’t use the center point of Aries to measure our day.
That extra four minutes comes into play because we look at the Sun to measure our day and as we’re moving around the Sun and spinning the Sun is kind of something we have to catch up to right. Every day we’re, going one 360 sixths of a way around the Sun.
So as we turn, the Sun, isn’t going to hit the exact same point every day and it turns out to make up. The difference is about four minutes, so thus we get a 24 hour day. So at one point people used this system in their various cities around the world to calculate their local time at home.
But if your city uses that and so does the neighboring city your times, aren’t going to match right. So it would be noon where you are and 12:05 a city an hour away and then a different time: 12, 10 or 12 15.
A city even further away and that’s, just not practical. This is before they had time zones and specifically set up chunks of area that would accommodate for a whole time period. In 1884, the Royal Observatory at Greenwich established that when the Sun is due south at that spot in Greenwich England, it is 12:00 noon and that was considered.
Greenwich Mean Time GMT and the rest of the world based all of time off of Greenwich Mean Time. Congratulations! England, you & # 39, ve done it, but this is just how long it takes to rotate. Why did we divide it into 24 segments? Because really the rotation is a natural process.
It’s organic there’s. No division of 24 segments of the day, so why did we pick that number and not something you know like 10 or you know, half of 24, 12 or 8, or something else or more? You know 50.
It’s. All thanks to the ancient Egyptians, many historians credit them with dividing up the day. First, they divided the day and night into twelve parts. Each ten parts were for day and night, one hour, each for dawn and dusk.
Why twelve is a little different, so they guess that Egyptians used twelve s to count see you probably think that you have ten fingers and thus ten is the easiest way to count anything right base. Ten ten fingers, ten toes it’s easy.
However, Egyptians they believed, didn’t use the number of fingers to count, but instead finger joints. So this means they have three in each finger. Like look at your fingers, you got joints everywhere right that gets you base twelve four fingers, excluding the thumb.
Three in each finger and they use those knuckles to do the counting evidence dating back to 1500 BC, shows that they developed a sundial that was divided up into twelve. There were also evidences of water clocks dating back to 1400 BC, also divided into twelve, and further evidence shows ancient Egyptians used a series of twelve different stars to keep track of their night.
So the reason we have a 24-hour day is because the ancient Egyptians decided it and we just still use it today, but let’s. Go a little deeper on this, because the Earth’s orbit again is natural and Egyptians didn’t have fixed lengths to their hours.
It was just divided, remember the day and the night. So in the summer you’d. Have longer hours during the day and shorter hours at night, 60-minute hours that didn’t come around until another group, the ancient Sumerians one of the earliest sophisticated civilizations, and they emerged around 4000 BC in what is now known as southern Iraq and later Became Babylonia anyway, so Sumerians they loved the number 60.
We use base 10 for counting. You know: 10 fingers 10 toes ancient Egyptians. They use base 12 because of all their little finger joints and Sumerians. They used base 60. They came up with 360 degrees in a circle and 60 times six three-sixty, so they divided up their day into 360 different parts equaling about 4 minutes.
Each and one theory is that they estimated years as well and that’s. Why we got 360 days there or that the Sun moves about 1 degree per day. Others think 60 was kind of the magic number, because it can be divisible by 1, 2, 3, 4, 5 & amp 6, so kind of special.
In that way, 60 wasn’t just special to one group of people. We still use it for a lot of things. Today. 60 was the common base number for time and angles and geographic coordinates and latitude and longitude.
It was used by the Greeks in late BC and early AD and around 150 AD Claudius Ptolemy, divided 360 degree, lines of latitude and longitude into 60. Smaller parts called minutes and then divided those 60 smaller parts into seconds.
So that’s. Where we get 60 minutes and 60 seconds, but it still wasn’t a timekeeping thing. It was a navigational thing and early clocks displayed hours in parts of two three or four and sometimes twelve, the first mechanical clocks to have 60 minutes.
In an hour that wasn’t until the sixteenth century, that’s, pretty recent as time went on. Science took what we learned from all of these ancient people, the ancient Greeks and Sumerians, and Egyptians as well as people in China and others that we’re all trying to figure out how to measure this very natural period of rotation.
And they created this specification for how exactly we should measure time in the 1950s that’s when they invented atomic timekeeping. They used this system that was very human, very much a collaboration of all of humanity and they created a system that said, okay.
This is exactly how long a second will be in 1967. The second was finally officially defined as 9,192,631,770 energy transitions or vibrations of a cesium atom. I know really easy to remember. The International Bureau of weights and measures is the official world timekeeper.
They keep the coordinated Universal Time. You can google it it’s very easy to find, and this is why today we still use seconds because we’ve, measured them, we’ve got them figured out, and that is that so there it is, that’s a day we came up with it kind of as a group.
It definitely has a feeling of day by committee and we broke it down literally into billions of seconds based on atomic vibrations. If you want more awesome information, make sure you click on the sidebar for another episode on this whole series, and you can find out about the week in the month in the year and a little more about the year.
Actually it’s, going to be really cool, make sure you subscribe, so you get further episodes of dnews plus and come find us on Twitter. You can find the show at dnews. You can also find me at trace Dominguez