Radiometric dating science definition
Series of events can be referred to a time scale, which is an ordered set of times derived from observations of some phenomenon.
Two independent, fundamental time scales are those called dynamical—based on the regularity of the motions of celestial bodies fixed in their orbits by gravitation—and atomic—based on the characteristic frequency of electromagnetic radiation used to induce quantum transitions between internal energy states of atoms.
Numerous time scales have been formed; several important ones are described in detail in subsequent sections of this article.
The abbreviations given here are derived from English or French terms.
A calendar (JD) in accordance with a system proposed in 1583 by the French classical scholar Joseph Scaliger and named in honour of his father, Julius Caesar Scaliger.
In this system days are numbered consecutively from 0.0, which is identified as Greenwich mean noon of the day assigned the date Jan.
That is, a clock displaying the time according to one of these scales would not—over an extended interval—show a change in its rate relative to that of a clock displaying time according to the other scale.Such phenomena make up much of the subject matter of astronomy, physics, chemistry, geology, and biology.The following sections of this article treat time measurements based on manifestations of gravitation, electromagnetism, rotational inertia, and radioactivity.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.