Definition

Noun: - Time measured by the apparent motion of the stars: Sidereal time is a timekeeping system based on the Earth's rotation relative to the distant, fixed stars, rather than the Sun. One sidereal day is the time it takes for a given star to return to the same position in the sky.

Usage

Sidereal time is a precise astronomical concept used for celestial navigation and telescope pointing. - Astronomers use sidereal time to locate celestial objects with their telescopes. - A sidereal day is approximately 23 hours, 56 minutes, and 4 seconds of mean solar time.

Advanced Usage

• Local Sidereal Time (LST): The sidereal time at a specific observer's longitude on Earth. It indicates which stars are on the observer's meridian.
  • The observatory's computer automatically calculates the Local Sidereal Time for accurate tracking.
• Greenwich Sidereal Time (GST): Sidereal time measured at the prime meridian (0° longitude) in Greenwich.

Variants and Related Words

• Sidereal Day: The time period of one rotation of Earth relative to the vernal equinox, about 4 minutes shorter than a solar day.
• Sidereal Year: The orbital period of the Earth around the Sun relative to the fixed stars.

Synonyms

• Star time: An informal term referring to time measured by stellar motion.

Notes

Sidereal time is not used for civil timekeeping in daily life, as it is not synchronized with the solar day and the cycle of daylight. Its primary application is in the field of astronomy.

Noun

1. measured by the diurnal motion of stars