Convert day (sidereal) to second

day (sidereal)

Definition: Day (sidereal) is a measure of time duration. For conversion purposes, its value is 86164.09 times the reference unit, second.

second

Definition: A second is the base unit of time in the International System of Units (SI). It is defined based on cesium frequency, ΔνC, "by taking the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom to be 9,192,632,770 when expressed in hertz, which is equal to s-1." This definition was adopted in late 2018, and is largely the same as the previous definition, except that the conditions are more rigorously defined.

History/origin: Unlike many units that have had numerous definitions throughout history, the second has only had four different definitions. The second was historically defined as 1/86400 of a day in 1832, which was based on the definition of a day as the approximate amount of time required for the Earth to complete a full rotation cycle relative to the sun. The second was also defined as a fraction of an extrapolated year in the late 1940s with the advent of quartz crystal oscillator clocks. This resulted in a second defined as "1/31,556,925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time," in 1956. This definition was adopted as part of SI in 1960. In 1967, the second was defined exactly as "9,192,631,770 times the period of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom." This definition has since been updated as of late 2018 to be more rigorously defined, but otherwise, is effectively the same. This new rigor does not affect how the second is used in everyday life.

Current use: As the SI base unit of time, the second and its multiples are ubiquitous. There are few, if any, modern applications in which time is measured in a form other than the second and its multiples.