Convert Second (s) to Hour (Sidereal) (h (sidereal)) instantly.
About these units
Second (s)
The second is the fundamental SI unit of time and the basis for nearly every modern timing system, from everyday clocks to astronomical calculations and quantum physics. Historically, the second was defined as 1/86,400 of a mean solar day—reflecting Earth's rotation. But because Earth's rotation is not perfectly constant, this definition proved insufficient for scientific precision. Today, the second is defined by the vibration frequency of the cesium-133 atom, specifically 9,192,631,770 oscillations of its hyperfine transition. This atomic definition gives the second extraordinary accuracy and stability, enabling technologies like GPS, satellite communications, deep-space navigation, and particle physics experiments. The second sits at the intersection of human history and cutting-edge physics: once tied to the apparent motion of the Sun, it is now anchored to a universal atomic constant, making it one of the most precisely defined units in science.
Hour (Sidereal) (h (sidereal))
A sidereal hour is 1/24 of a sidereal day, approximately 59 minutes and 50.17 seconds of solar time. Astronomers use sidereal hours to measure right ascension and to coordinate telescope pointing systems. Because stars return to the same apparent position after exactly one sidereal day, sidereal hours offer a stable celestial reference frame. While not used in daily life, sidereal hours are indispensable for precision observation of the universe.