Convert Day (Sidereal) (d (sidereal)) to Planck Time (tₚ) 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.
Planck Time (tₚ)
Planck time is the smallest meaningful unit of time in known physics, defined as the time it takes light to travel one Planck length. It equals approximately 5.39 × 10⁻⁴⁴ seconds. Below the Planck time, current theories of spacetime—General Relativity and Quantum Mechanics—break down, and we enter a regime where quantum gravity dominates. Planck time defines the theoretical boundary of the earliest moments of the universe, immediately after the Big Bang, before classical spacetime emerged. It is not a unit we can measure directly; rather, it represents a fundamental limit set by nature's constants, including the speed of light, the gravitational constant, and Planck's constant. The Planck time is the frontier where physics transitions from the known into the speculative—where time itself may become granular, discontinuous, or fundamentally different from the human conception.