Calendars and time
UT1
Direct answer
UT1 is the Universal Time scale determined from Earth rotation angle relative to the celestial reference system.
$0 today, then $12/month after 7 days. Cancel anytime.
At a glance
- Found in
- Calendars & Timekeeping
- Related
- International Atomic Time, UTC Offset, Calendar, Julian Date
UT1 is modern Earth-rotation time.
A cycle or timeline schematic for comparing the named timekeeping concept.
What does your own chart say about you?
Choose love, work or purpose. Your reading is written from your chart. Your reading uses your own birth details.
Walk through Alex’s whole example first
The Road of AgesSee the turning points of your whole life, from your birth date
See your road's shape
Prefer to explore first?
The Road of AgesThe turning points of your whole life, from your own chart
Walk my road
Free, by email
Your daily Almanac letter
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
The story behind UT1
Very long baseline interferometry and other space-geodetic techniques now determine UT1 more accurately than older transit observations.
Why UT1 matters
UT1 connects astronomical pointing and Earth orientation to the actual, slightly irregular rotation of the planet.
How to read UT1
UT1 speaks to Earth rotation angle, high-precision sidereal calculations, and transforming celestial directions to Earth-fixed coordinates.
Where readings of UT1 go wrong
A common error is to treat UT1 as perfectly uniform or use UTC as an exact substitute in precision Earth-orientation work.
Sources and editorial method
Research references used for this entry include:
- IERS Glossary: Universal Time (UT1) - Official definition of UT1 as Earth-rotation time and its publication as UT1-UTC.
- U.S. Naval Observatory: Universal Time - Official explanation of Earth-rotation time and the Universal Time family.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Apply the current UT1 correction
A definition tells you what it is; your own birth chart tells you what it means for you. The Oracle casts your real chart and answers for your love, your work, and your year ahead, in conversation. It opens with the 7-day Seeker trial.
Speak with the OracleRelated terms
More in Calendars & Timekeeping
- Astronomical Year Numbering
- Civil Calendar
- Draconic Year
- Golden Number
- ISO Week Date
- Local Sidereal Time
- Proleptic Gregorian Calendar
- Solar Calendar
From the reference page to your own chart
Every word here
is in your own chart.
- A personal reading about love, work or purpose, written from your chart
- A practical next step to consider
- It opens with 7 days free, with the AI Oracle and daily guidance
$0 today, then $12/month after 7 days. Cancel anytime.
Common questions
What is UT1?
UT1 is the Universal Time scale determined from Earth rotation angle relative to the celestial reference system.
What do people get wrong about UT1?
A common error is to treat UT1 as perfectly uniform or use UTC as an exact substitute in precision Earth-orientation work.
Free, by email
The Almanac, in your inbox at 7
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
