In the past, one day on Earth ... only 22 hours

Within a hundred years, the day on Earth only increased by a few milliseconds. But within the past few decades, science has been able to measure this change with extreme precision.

The pace of time

By using atomic clocks and super-accurate measurements of distant quasars (sources of very strong electromagnetic radiation, like a star), we can measure the length of a day in billionth of a second. These measurements are so accurate that we can observe different fluctuations such as earthquakes in the length of a day.

These fluctuations create challenges and many different questions. For a longer period of time, how has the Earth's rotation changed?

One of the reasons why the days on Earth are getting longer and longer is that the Moon's gravity acts on our oceans.

The tide exerts force on the Earth, gradually slowing its rotation. This process took place over millions of years, making Earth's day shorter than it is now, so in the past one year there are more days now.

We know these impacts based on geological records. It tells us 620 million years ago, an Earth day about 22 hours long. However, efforts to measure the length of a day at the present time and geological record are really difficult to implement.

Observing a solar eclipse helps scientists measure time.(Photo: Internet).

Hundreds of years ago, no clock was accurate enough to measure this variation. And the length of a day fixed by its rotation has prevented researchers from performing any comparison. But recently, science has found a way to study the change in the length of days on Earth.

Past observations

Although our ancestors for centuries haven't had accurate clocks, they are still talented astronomers. They observe and record astronomical events like the Moon obscuring the brightness of stars, as well as eclipses. The appearance of these events depends very much on the time and place of the observer.

For example, if an astronomer in this city sees the Moon pass in front of a star on a night, the astronomer in the next city will only see the Moon approaching the star. only

By comparing these observations to the actual time of the event, plus calculating from the orbital motions of the Earth and the Moon, we can know exactly when and where the event takes place. These astronomical events .

Comparing the time taken to observe each other, we obtain an average increase in the time of day in a day. People calculate, every century, the day on Earth is about 1.8 milliseconds long.

There are two interesting things about this result.The first is that the researchers were surprised to know this number only through historical documents. The previous ones had made observations that lasted for more than 2.5 millennia and they were written in different languages ​​as well as observations made in many places around the world. Collecting them and verifying - is truly a great effort.

The second is that the measured result is lower than the hypothesis that the researchers gave, based on the tidal effects of the Moon. The cause of this may be due to the change in the overall shape of the Earth.

For example, we know that ice melting from the last ice age (about 10,000 years ago) caused pressure at the Earth's poles, making it more spherical. This makes the day on Earth a little shorter. The combination of these two effects has resulted in the results we see.

This research work is a great testament to the fact that history can talk to us. If we listen carefully, we can even see the change of time .