# Listen: Adams, Ashley Hamer, Mohammed Chiffon discussed on Curiosity Daily

"What's a second? Someone couldn't have just made a moving object look at ticking hand and a and said sixty ticks is one minute and sixty minutes is an hour and so on. So who decided what a second is? Well, before we divided time into seconds. We divided time into days and hours historians credit. The Egyptians with being the first to divide the day into equal parts while the counting system. We're familiar with his base ten you have ten fingers after all the ancient Egyptians had a base twelve system. They counted on their finger joints using their thumbs a pointer, cool, right? As a result, they divided the day into twelve parts and the night into twelve parts, which we know from seeing the sun dials. They left behind the subdivision of each hour into sixty minutes in each minute into sixty seconds started. With the Babylonians who had a base sixty counting system. You are gonna be counting to sixty using body parts, of course, but that's does have mathematical advantages. I don't have time to get into. Anyway, that definition of a second a sixtieth of a sixtieth of twenty fourth of a day or one eighty six thousand four hundred of the average solar day, which is the time. It takes the sun to come back to the same place in the sky continued to be the standard measure of a second until the twentieth century. See the average solar day actually changes length. So this definition wasn't exact enough for science. So in one thousand nine hundred they were like, okay instead of making it a fraction of the average solar day will make it a fraction of the specific solar day on January first nineteen hundred well that didn't really help things. You can't exactly go back and measure the length of that day. Still that definition lasted until nineteen sixty seven when the second got really specific scientists used their knowledge of the atom. To define a second. As get ready. Nine billion one hundred ninety two million six hundred thirty one thousand seven hundred and seventy periods of the radiation for a cesium one thirty three atom wolf that sounds way more complicated than counting to sixty on your body parts, I know, but scientists can make that measurement anywhere anytime, regardless of the amount of daylight this time of year, and that's key for ideal precision. A scientists has to be able to check their measurements in the lab not against some abstract concept like how long the day was in one thousand nine"

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