Comparing relative dating and radiometric dating
In this article, unless otherwise indicated, second (symbolized s) means the SI second; a minute (m or min) is 60 s; an hour (h) is 60 m or 3,600 s.An tropical year, whose period is that of the seasons, is the interval between successive passages of the Sun through the vernal equinox.Atomic clocks serve as the basis of scientific and legal clock times.A single clock, atomic or seconds dates to the ancient Egyptians.The equations of motion that define TDB include relativistic terms.
The adoption of the SI second, defined on the basis of atomic phenomena, as the fundamental time unit has necessitated some changes in the definitions of other terms.International Atomic Time (TAI; introduced in 1955) is covered in the section Atomic time.Accuracies of atomic clocks and modern observational techniques are so high that the small differences between classical mechanics (as developed by Newton in the 17th century) and relativistic mechanics (according to the special and general theories of Einstein in the early 20th century) must be taken into account.TAI and TDT differ from TDB by calculable periodic variations.Apparent positions of celestial objects, as tabulated in ephemerides, are corrected for the Sun’s gravitational deflection of light rays.atomic clock provides the most precise time scale.
Search for comparing relative dating and radiometric dating:
1, 4713 (MJD), defined by the equation MJD = JD - 2,400,000.5, begins at midnight rather than noon and, for the 20th and 21st centuries, is expressed by a number with fewer digits. 14, 1981 (Gregorian calendar date), corresponds to JD 2,444,923.0; the preceding midnight occurred at JD 2,444,922.5 and MJD 44,922.0.