Are the days equal to each other?

And, after all, are the days equal to each other? At first glance, everything is very simple. The earth rotates slowly and majestically. The period of time during which it makes a complete revolution around an imaginary axis is called days. The day contains 24 hours. What is the problem then? The complexity of the question posed will become immediately apparent as soon as we try to practically determine the length of the day.

And, after all, are the days equal to each other? At first glance, everything is very simple

Astronomical observatories have a special instrument designed to measure time from the stars. It is called a transit instrument. The design of the transit instrument is similar to an ordinary refractor telescope, but its optical axis is always located in the same plane - the plane of the celestial meridian. Looking through the eyepiece of the transit instrument, we see one horizontal and three vertical threads in the field of view. A bright star appeared in the field of view. The rotation of the Earth makes it quickly approach the line of the celestial meridian. Finally, she crossed the central vertical thread of the transit instrument. The astronomer must record this moment of its climax as accurately as possible. Indeed, by the time this star returns to the celestial meridian, exactly one day will have passed.

Until recently, it was believed that the Earth rotates perfectly uniformly. The best chronometers have been verified by observing the climax of the stars. If between the two culminations of the star the chronometer proceeded not 24 hours, but 0.1 seconds less, then the fault for this discrepancy was always attributed not to the Earth, but to the chronometer. It seemed obvious that in such cases it was not the Earth that began to rotate faster, but the chronometer was somewhat "behind". The conviction of the ideal uniformity of the Earth's rotation was based on experimental data.

But technology developed, the accuracy of measuring instruments was constantly growing, and finally it was possible to invent a quartz watch, which, in terms of its uniformity, significantly surpassed our Earth. It turned out that our planet rotates in "jerks", then with deceleration, then with acceleration. Quartz watches have debunked the illusions of the senses. With their accuracy in measuring time, not a trace remains of the past ideas about the uniformity of the Earth's rotation.

The discovered irregularities in the rotation of our planet can be divided into three groups. First of all, this is a systematic slowdown of the Earth's rotation caused by the action of tidal waves. When tidal waves run along the bottom of the seas and oceans, they "rub" against the earth's crust and thus, like brake pads, slow down the rotation of our planet. This deceleration is not great: for a whole century, the day increases by one thousandth of a second. In 1 million years, the day will become longer than the present day due to this effect by only 10 seconds!

The second group of irregularities in the Earth's rotation is periodic fluctuations in the length of the day caused by seasonal meteorological phenomena. It turns out that in autumn and winter, the Earth rotates on average more slowly than in spring and summer, and the difference in the length of the day reaches 0,03 seconds in one direction or another. In this case, the atmosphere affects the rotation of the Earth. Fallout of precipitation changes in a complex way the mass of the Earth's solid body, and it is not the same in different hemispheres. The change in mass also affects the rotation of the Earth.

The reasons for the irregularities in the third group are still unknown. These irregularities are in the nature of irregular "jerks", that is, unexpected accelerations or decelerations of the Earth's rotation. All of them are negligible: because of them, the magnitude of the day changes from day to day by no more than a thousandth of a second.

Thus, the main standard of time - the day - is highly variable. Strictly speaking, today is not equal to tomorrow. The duration of the next day will not be equal to 24 hours.