**How Many Seconds Are In a Day** – A day has 86,400 seconds. You want to know why? It is because a minute has 60 seconds, the hour has 60 minutes and the day has 24 hours, the equation is 60 x 60 x 24 = **86,400**.

## The Big Question is, Perhaps, Why Does a Second Last a Second?

The day (for short, is what it takes our planet to turn around itself) was not always “separated” in 24 hours but in the early days, when time began to count, the Egyptians used a day 12 hours.

Then the astronomers of Hipparchus (year 150 before Christ) and Ptolemy (year 150 after Christ) began to subdivide the day into a sexagesimal system to separate the hours, which in turn would be 1 part of 24 (and therefore the day began to have 24 hours). This system allowed us to use simple fractions like 1/4, 1/6, 1/12, or 1/2. At that time it was known that the second was 1/60 of a minute although there was no easy way to accurately determine it.

## The First Time The Second Could Be Measured Accurately

It took nearly 1,500 years for the 24-hour, 60-minute, and 60-second system to have the ability to accurately measure time in seconds. The first attempt was made by Marin Mersenne in 1644 with a pendulum system that had a length of 0.994 meters and its period of gravity was exactly 2 seconds, so one forward movement marked one second and another was marked when the pendulum went backward.

One of the most admirable things about ancient civilizations like the Aztecs was their complex mechanisms for calculating distances and time; Nowadays, however, we can use a simple multiplication to find out how many seconds a day has.

Years later, in 1670, a London watchmaker named William Clemente added a second pendulum to the original pendulum clock system created by Christiaan Huygens. Clemente took over 10 years to perfect the system, which was finally able to display the seconds at the bottom with surprising accuracy. This mechanism required little energy compared to the original pendulums, in addition to causing less friction and therefore less wear. Clemente’s system is considered the first reliable way to measure seconds and in a short time, his invention was copied by most British watchmakers, and then spread throughout Europe.

## The Second Most Accurate Is Not Many Years Old

The title seems like a paradox but it is not, since from the 20th century on, technology advanced enough to be more precise when determining a unit of time as important as the second.

During the 1940s, the definition of the second was that it was the temporal measure that lasted 1/86400 part of an average solar day.

In 1956, the second was determined to be: fraction 1/31,556,925.9747 of the tropical year for 1900, January 1 at 12 noon.

With the advent of the nuclear age, various engineers and physicists from the United States and England tried to create a way to measure the second most possible and they succeeded. They determined that one second was equal to the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom, and because this atom is so stable, it was defined as a standard for measuring time. and with it, the atomic clock was created, which has an error rate of 1 second in 30 million years.

This is something that is greatly appreciated in these times when we need perfect synchrony with satellites, the Internet, computers, and Smartphones.

**Also may interest you: **

## How Many Seconds Does a Day Have?

For starters, we know that the unit of time that follows a second is the minute and that it contains 60 seconds. If we also know that an hour contains 60 minutes we have that an hour will have 60 seconds multiplied by 60 minutes 60 × 60 = 3600 seconds. From there, it only remains to multiply the seconds that an hour has by the hours of the day, which represents 3600 seconds x 24 hours. **The result 3600 × 24 = 86400 seconds has one day.**