Convert Day (Sidereal) (d (sidereal)) to Second (s) instantly.
About these units
Day (Sidereal) (d (sidereal))
A sidereal day is the time Earth takes to rotate exactly 360 degrees relative to the distant stars—about 23 hours, 56 minutes, 4 seconds. In contrast, the solar day is slightly longer because Earth advances in its orbit each day and must rotate extra degrees for the Sun to appear in the same position in the sky. Sidereal days are fundamental to astronomy: telescopes use sidereal time to track stars, which appear in the same position in the sky at the same sidereal moment each night. This unit anchors astronomical observation to the cosmos rather than to the Sun.
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.