Earth days increase by an average of 1.78 ms per century


    Average long-term deceleration of the Earth’s rotation

    In 1995, a pair of scientists from the University of Durham (Great Britain) and the office of the Royal Maritime Almanac carefully studied historical information about solar and lunar eclipses from 700 BC. to 1990 from Babylon, Ancient Greece, Arab dominions, Ancient China and Europe - all these civilizations possessed advanced knowledge of astronomy and kept records of solar and lunar eclipses. The analysis of historical data in conjunction with modern information made it possible for the first time to draw up a graph of long-term fluctuations in the rotation of our planet. The theory was confirmed that the Earth does not rotate at the same speed. It periodically accelerates and slows down, with a long-term tendency to a gradual deceleration.

    21 years later, the same scientistsdeveloped an updated historical graph of the Earth's rotation. It includes new historical data: about 25% more information about solar eclipses from Babylon, as well as adjusted data about eclipses from Ancient China, in which inaccuracies due to interpretation errors were corrected. In addition, scientists took a new archive of lunar eclipses from 1623 to 2015 , which was compiled taking into account the latest and most accurate ephemeris of the moon, the position of the stars and the contour of the moon during eclipses. Information obtained from NASA's Jet Propulsion Laboratory.

    After updating the eclipse tables from historical records, scientists calculated the difference between the eclipse time in relative universal time (Universal Time, UT) and absolute earth time(TT). Earth time is a modern astronomical standard developed by the International Astronomical Union to determine the time of astronomical observations made from the surface of the Earth. It is designed according to the gravitational model of the solar system and does not depend on actual changes in the speed of rotation of the Earth.

    The time delta (ΔT) in the table and in the graphs corresponds to the difference between TT and UT. Since mid-1955, when high-precision atomic clocks began to operate on Earth, TT is defined as atomic clock time (TAI) plus 32.184 seconds. On a TT scale, one day is defined as 86,400 seconds SI. On the UT scale, one day corresponds to the average value of sunny days, based on the average period of the Earth's revolution around its axis.

    Current fluctuations in the Earth's rotation speed are accurately determined by information from satellites in Earth orbit and the relative position of the Earth and the Moon. Laser rangefinders made it possible to accurately calculate tidal acceleration in the Earth-Moon (n) system: this is −25.82 ± 0.03 ′ ′ cy −2 .



    Accordingly, we can accurately calculate the theoretical dependence of the Earth's rotation speed on tidal acceleration.



    Therefore, ΔT for changing rotation under the influence of tidal acceleration will change with time as a parabola:



    In this formula, t corresponds to the Julian centuries after 1820.



    It should be noted that due to the large mass of the Moon (approximately 1/81 of the Earth’s mass), the Earth-Moon system can be considered as a binary planetary system, and not as a planet with a satellite.

    Data from laser rangefinders on the Moon and information on tidal acceleration is available only for the past about 50 years, but this formula is quite applicable to the historical data of astronomical observations, because the system of the Earth and the Moon has not changed.

    Scientists have tried to determine how other unknown factors other than tidal acceleration influenced the speed of rotation of the Earth in past centuries.

    Here's what the diagram of ΔT changes looks like according to the results of all observations until 1600, more precisely - until the total solar eclipse of 1567.



    Measurements after 1600 and especially after 1700 with the use of more advanced instruments (telescopes) significantly reduced the measurement error.

    Here is the diagram of ΔT changes according to the observations from 1623 to 2015.



    If we use the aforementioned parabola and present it in a straight line, then long-term fluctuations in the Earth's rotation speed form the following picture.



    Scientists conclude that only with tidal acceleration it is impossible to explain fluctuations in the Earth's rotation speed. Obviously, other forces influence the planet’s rotation. For example, it can be a combination of glacioisostasis (vertical movements of the earth's surface) and the gravitational interaction of the core with the Earth’s mantle.

    Based on the analysis of all historical data, we can calculate the average long-term deceleration of the Earth’s rotation, which is about 1.78 milliseconds per century.

    The scientific work and all the source data in tabular form was published on December 7, 2016 in the journalProceedings of the Royal Society are publicly available for further processing by astronomers and astrologers (representatives of this pseudoscience also prefer to use real scientific data).

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