Dictionary term
Sidereal Time
Direct answer
Sidereal Time measures Earth's rotation relative to the stars and indicates which right ascension is crossing the local meridian.
Sidereal Time is star-based rotational time used to orient the sky.
Sidereal Time is star-based rotational time used to orient the sky.
A cycle or timeline schematic for comparing the named timekeeping concept.Quick reference
- Use when
- Use Sidereal Time for telescope pointing, observatory planning, and explaining why stars rise about four minutes earlier on successive solar days.
- Do not use it for
- Do not confuse a sidereal day with a 24-hour civil solar day.
- Reference category
- Calendars & Timekeeping
- Related terms
- Calendar, Solar Calendar, Lunar Calendar, Lunisolar Calendar
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The story behind Sidereal Time
Observatories used repeated stellar transits and precise clocks to establish sidereal time and test timekeeping.
Sidereal Time in spiritual tradition
Sidereal time reveals a daily rhythm measured against distant stars rather than the Sun.
Sidereal Time: fact and faith, kept distinct
This is a factual astronomy, calendar, Earth-science, cultural, or historical reference. It can support wonder at the created order without becoming a claim of fate, worship, or private revelation.
Sidereal Time in numerology
Sidereal Time is not a numerology claim. Any numbers attached to it should retain their ordinary scientific, calendrical, navigational, or historical meaning unless a separate symbolic interpretation is clearly labeled.
Why Sidereal Time matters
It lets observers and telescopes connect clock-like time with the part of the celestial sphere currently on the meridian.
Sidereal Time at work: an example
When local sidereal time is six hours, objects near right ascension six hours are crossing the local meridian.
Where interpretation stops
Sidereal Time is presented as sourced astronomy, calendrical, Earth-science, cultural, or instrument-history reference. Definitions should distinguish measured phenomena from civil convention and historical interpretation, preserve location and time dependencies, and avoid turning factual sky data into a deterministic personal claim.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Computing Approximate Sidereal Time - Official explanation and method for Greenwich and local sidereal time.
- U.S. Naval Observatory: Astronomical Almanac Glossary - Reference definitions for astronomical coordinates, events, calendars, and time scales.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Also appears in
- Calendars & Timekeeping
- Aliases
- None listed
- Last updated
- 2026-07-15
Find the sky on your meridian
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Speak with the OracleRelated terms
More in Calendars & Timekeeping
- Universal Time
- Apparent Solar Day
- Calendar Year
- Double Dating
- Geocentric Coordinate Time
- Intercalation
- Local Apparent Solar Time
- Old Style Date
Common questions
What is Sidereal Time?
Sidereal Time measures Earth's rotation relative to the stars and indicates which right ascension is crossing the local meridian.
How is Sidereal Time used in an almanac?
Use Sidereal Time for telescope pointing, observatory planning, and explaining why stars rise about four minutes earlier on successive solar days.
What should I avoid when interpreting Sidereal Time?
Do not confuse a sidereal day with a 24-hour civil solar day.
