Definition

1. Noun:
   • A unit of time equal to 1/24th of a sidereal day: A sidereal hour is a measurement of time based on the Earth's rotation relative to distant stars, rather than the Sun. It is used primarily in astronomy.

Usage

• The term "sidereal hour" is a specific scientific unit. It is used in contexts discussing celestial navigation, astronomy, and precise timekeeping relative to the fixed stars.
• It is typically used with precise numerical values or in comparisons with solar time.

Examples

• Noun:
  • The telescope's tracking motor is calibrated to move at a rate of one sidereal hour per hour of clock time.
  • A sidereal hour is approximately 59 minutes and 50 seconds of standard solar time.

Advanced Usage

• "Sidereal hour angle": A related astronomical coordinate measured westward along the celestial equator from the vernal equinox, often expressed in hours, minutes, and seconds of sidereal time.
  • The star's position was given in terms of its sidereal hour angle.

Variants and Related Words

• Sidereal time (n): Timekeeping system based on the Earth's rotation relative to the vernal equinox.
  • Sidereal time is essential for locating celestial objects with a telescope.
• Sidereal day (n): The time it takes for the Earth to complete one rotation relative to the distant stars, which is about 23 hours, 56 minutes, and 4 seconds of solar time.
  • A sidereal day is shorter than a solar day.

Synonyms

• Astronomical hour: (Less common) A term sometimes used interchangeably with sidereal hour in specific contexts.

Notes

• There are no common idioms or phrasal verbs associated with this precise scientific term. Its usage is strictly technical.

Noun

1. 1/24 of a sidereal day