“The length of the tropical year, the time it takes for the Earth to complete one orbit around the Sun, is not a constant value. It is affected by various factors, including the gravitational influences of other planets in the solar system and the shape of the Earth’s orbit.
Over time, the length of the tropical year has varied slightly. In general, the length of the tropical year has been gradually increasing over the past few thousand years. This is due to several factors, including the slowing of the Earth’s rotation, the influence of the Moon’s gravity on the Earth’s orbit, and the effects of solar radiation on the Earth’s atmosphere and surface.
The rate at which the tropical year is increasing is very small, however, and is not easily noticeable over short time periods. In fact, the length of the tropical year has increased by only about 1.5 seconds over the past century.”
The mean tropical year on January 1, 2000, was 365.2421897 or 365 ephemeris days, 5 hours, 48 minutes, 45.19 seconds. This changes slowly; an expression suitable for calculating the length of a tropical year in ephemeris days, between 8000 BC and 12000 AD is
where T is in Julian centuries of 36,525 days of 86,400 SI seconds measured from noon January 1, 2000 TT.
The mean tropical year on January 1, 2000, was 365.2421897 or 365 ephemeris days, 5 hours, 48 minutes, 45.19 seconds. This changes slowly; an expression suitable for calculating the length of a tropical year in ephemeris days, between 8000 BC and 12000 AD is{\displaystyle 365.2421896698-6.15359\times 10^{-6}T-7.29\times 10^{-10}T^{2}+2.64\times 10^{-10}T^{3}}
where T is in Julian centuries of 36,525 days of 86,400 SI seconds measured from noon January 1, 2000 TT. Wiki