What does Sidereal mean on CalculationTime?
Sidereal time is why a star returns to nearly the same place in the sky about four minutes earlier each solar day.
Glossary term
Sidereal
Sidereal means measured relative to the stars rather than the Sun. Sidereal framing matters for star clocks, sky maps and instruments that track the rotating sky.
History of the term
Sidereal comes from the Latin sidus, meaning star. Astronomers use it because the stars provide a stable reference frame for Earth’s rotation.