Minute to Sidereal Day Converter
Convert minutes to sidereal days with our free online time converter.
Quick Answer
1 Minute = 0.000696 sidereal days
Formula: Minute × conversion factor = Sidereal Day
Use the calculator below for instant, accurate conversions.
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All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.
Minute to Sidereal Day Calculator
How to Use the Minute to Sidereal Day Calculator:
- Enter the value you want to convert in the 'From' field (Minute).
- The converted value in Sidereal Day will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Time category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Minute to Sidereal Day: Step-by-Step Guide
Converting Minute to Sidereal Day involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Minute = 0.000696346 sidereal daysExample Calculation:
Convert 60 minutes: 60 × 0.000696346 = 0.0417807 sidereal days
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.
Need to convert to other time units?
View all Time conversions →What is a Minute and a Sidereal Day?
The minute (symbol: min) is a unit of time equal to 60 seconds or 1/60 of an hour (exactly 0.016̄ hours, or approximately 0.0167 hours).
Official SI-derived definition: Since the second was redefined atomically in 1967, one minute equals exactly 60 seconds, where each second is the duration of 9,192,631,770 periods of radiation from caesium-133 atoms. Therefore:
- 1 minute = 60 × 9,192,631,770 = 551,558,906,200 caesium-133 oscillations
Practical conversions:
- 1 minute = 60 seconds (exact)
- 1 minute = 0.016666... hours (1/60 hr, exact)
- 1 hour = 60 minutes (exact)
- 1 day = 1,440 minutes (24 × 60)
- 1 week = 10,080 minutes (7 × 24 × 60)
- 1 year (365 days) = 525,600 minutes (memorably featured in the musical Rent)
The minute is not an SI base unit, but it is accepted for use with the SI alongside hours, days, and other traditional time units due to its universal cultural importance and practical utility.
Why 60?
The choice of 60 comes from ancient Babylonian sexagesimal (base-60) mathematics, developed around 3000 BCE. The Babylonians chose 60 because it's highly divisible:
- Factors of 60: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60 (12 factors!)
- This makes fractions like 1/2 (30 min), 1/3 (20 min), 1/4 (15 min), 1/5 (12 min), 1/6 (10 min) all whole numbers
- Contrast with decimal: 100 only has factors 1, 2, 4, 5, 10, 20, 25, 50, 100 (9 factors, and divisions like 1/3 = 33.33...)
This mathematical convenience made base-60 ideal for astronomy, geometry, and timekeeping—fields requiring frequent division. The system persists today in our 60-minute hours, 60-second minutes, and 360-degree circles (6 × 60).
What Is a Sidereal Day?
A sidereal day is the time required for Earth to complete one full rotation (360 degrees) on its axis relative to the fixed background stars.
Precise value: 1 sidereal day = 86,164.0905 seconds (mean sidereal day) = 23 hours, 56 minutes, 4.0905 seconds
Sidereal vs. Solar Day
Sidereal day (stellar reference):
- Earth's rotation relative to distant stars
- Duration: 23h 56m 4.091s
- Used by astronomers for telescope pointing
Solar day (Sun reference):
- Earth's rotation relative to the Sun
- Duration: 24h 00m 00s (mean solar day)
- Used for civil timekeeping (clocks, calendars)
The difference: ~3 minutes 56 seconds
Why Are They Different?
The sidereal-solar day difference arises from Earth's orbital motion around the Sun:
- Start position: Earth completes one full 360° rotation relative to stars (1 sidereal day)
- Orbital motion: During that rotation, Earth has moved ~1° along its orbit around the Sun
- Extra rotation needed: Earth must rotate an additional ~1° (~4 minutes) to bring the Sun back to the same position in the sky
- Result: Solar day = sidereal day + ~4 minutes
Analogy: Imagine walking around a merry-go-round while it spins. If you walk one full circle relative to the surrounding park (sidereal), you'll need to walk a bit farther to return to the same position relative to the merry-go-round center (solar).
One Extra Day Per Year
A surprising consequence: There is one more sidereal day than solar day in a year!
- Solar year: 365.242199 solar days
- Sidereal year: 365.256363 sidereal days
- Extra sidereal days: 366.256363 - 365.242199 ≈ 1 extra day
Why? Earth makes 366.25 full rotations relative to the stars during one orbit, but we only experience 365.25 sunrises because we're moving around the Sun.
Note: The Minute is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Sidereal Day belongs to the imperial/US customary system.
History of the Minute and Sidereal Day
of the Minute
Ancient Babylonian Origins (c. 3000 BCE)
The foundation of the minute lies in the Sumerian and Babylonian sexagesimal (base-60) number system developed in ancient Mesopotamia around 3000 BCE. The Babylonians used this system for:
- Astronomical calculations: Dividing the celestial sphere and tracking planetary movements
- Geometric measurements: Dividing circles into 360 degrees (6 × 60)
- Mathematical computations: Facilitating complex fractions and divisions
- Calendar systems: Organizing time into convenient subdivisions
Cuneiform tablets from this era show sophisticated astronomical observations recorded using base-60 divisions, laying groundwork for the eventual minute.
Greek Astronomical Adoption (150 CE)
The ancient Greeks, particularly Claudius Ptolemy (c. 100-170 CE), formalized the division of hours and degrees into 60 parts in his astronomical treatise Almagest. Ptolemy used Latin terminology inherited from earlier traditions:
- "pars minuta prima" (first minute/small part) = 1/60 of a degree or hour → modern minute
- "pars minuta secunda" (second minute/small part) = 1/60 of a minute = 1/3600 of a degree/hour → modern second
These terms were primarily used for angular measurement in astronomy and navigation (describing positions of stars and planets), not yet for practical daily timekeeping.
Medieval Islamic and European Transmission (800-1300 CE)
During the Islamic Golden Age (8th-13th centuries), Arab astronomers and mathematicians preserved and expanded on Greek astronomical texts, continuing to use the 60-part division system.
When European scholars translated Arabic astronomical manuscripts in the 12th and 13th centuries (particularly at translation centers in Toledo, Spain, and Sicily), they reintroduced the Latin terms "pars minuta prima" and "pars minuta secunda" to European scholarship.
However, these remained primarily theoretical and astronomical units. Practical timekeeping in medieval Europe relied on:
- Sundials (showing hours)
- Water clocks (clepsydrae)
- Candle clocks (burning time)
- Church bells marking canonical hours (Matins, Prime, Terce, Sext, None, Vespers, Compline)
None of these devices tracked minutes—they were too imprecise, and daily life didn't require such granularity.
Mechanical Clocks Emerge—But No Minute Hands (1300s)
The first mechanical clocks appeared in Europe around 1280-1300, installed in church towers and public buildings. Early examples include:
- Salisbury Cathedral clock (England, c. 1386) - still running, one of the oldest working clocks
- Wells Cathedral clock (England, c. 1390)
- Prague Astronomical Clock (Czech Republic, 1410)
Crucially, these early clocks had only an HOUR hand. They were too inaccurate (losing or gaining 15-30 minutes per day) to justify displaying minutes. The concept of "being on time" to the minute was essentially meaningless when clocks could drift that much daily.
Pendulum Revolution: Minutes Become Meaningful (1656)
The transformative moment for minute-level timekeeping came with Christiaan Huygens' invention of the pendulum clock in 1656. This invention improved timekeeping accuracy from errors of 15 minutes per day to less than 15 seconds per day—a roughly 60-fold improvement.
Why pendulums revolutionized accuracy:
- A pendulum's swing period depends only on its length and gravity (Galileo's discovery, 1602)
- Length is constant → period is constant → highly regular "tick"
- Formula: Period = 2π√(L/g), where L = length, g = gravitational acceleration
- A 1-meter pendulum has a period of approximately 2 seconds—perfect for timekeeping
With this accuracy, displaying minutes became both practical and necessary. Clockmakers began adding minute hands to clock faces around 1660-1680.
Minute Hands Become Standard (1670-1750)
By the late 17th century:
- 1670s: Quality clocks routinely featured minute hands
- 1680s: Balance spring invention (Huygens and Robert Hooke) further improved accuracy, enabling portable watches to track minutes
- 1700s: Minute display became universal on both public clocks and personal timepieces
- 1761: John Harrison's H4 marine chronometer achieved extraordinary accuracy (losing only 5 seconds on a 81-day voyage), revolutionizing navigation
The minute transformed from an astronomical abstraction to a practical daily measurement, changing social organization fundamentally.
Societal Impact: The "Minute Culture" (1800s)
The 19th century saw the rise of minute-precise scheduling, driven by:
-
Railroad timetables (1840s onward):
- Trains required synchronized schedules to prevent collisions
- Railway time standardized clocks across regions
- Timetables specified arrivals/departures to the minute
- This drove development of time zones and standard time
-
Factory work and "time discipline" (Industrial Revolution):
- Factory shifts started at precise times (e.g., 7:00 AM, not "dawn")
- Workers punched time clocks tracking arrival to the minute
- The concept of "being late" became economically significant
- Frederick Winslow Taylor's "scientific management" (1880s-1910s) measured work tasks in minutes and seconds
-
Urban life coordination:
- Meeting times specified to the minute
- Public transportation schedules
- School bell systems marking class periods
This represented a profound cultural shift: pre-industrial societies organized time around seasonal cycles, sunlight, and approximate "hours." Industrial society required minute-level coordination of human activity.
Atomic Age: Minutes Defined by Seconds (1967-Present)
When the second was redefined in 1967 based on caesium-133 atomic oscillations (9,192,631,770 cycles = 1 second), the minute automatically inherited this precision:
1 minute = exactly 60 × 9,192,631,770 caesium oscillations = 551,558,906,200 caesium oscillations
Modern atomic clocks maintain this definition with extraordinary stability, losing less than 1 second in 100 million years. This means the minute is now defined with sub-nanosecond precision, far beyond any practical human need but essential for:
- GPS systems (requiring nanosecond synchronization)
- Financial trading (high-frequency trading in microseconds)
- Telecommunications (network synchronization)
- Scientific experiments (particle physics, gravitational wave detection)
The "525,600 Minutes" Cultural Moment (1996)
In 1996, the musical Rent by Jonathan Larson opened on Broadway, featuring the iconic song "Seasons of Love," which begins:
"Five hundred twenty-five thousand, six hundred minutes... How do you measure, measure a year?"
This number—525,600 minutes = 365 days × 24 hours × 60 minutes—became a cultural touchstone, highlighting the minute as a unit for measuring the passage of life itself, not just scheduling appointments.
Ancient Observations (2000-300 BCE)
Babylonian astronomy (circa 2000-1500 BCE):
- Babylonian astronomers tracked stellar positions for astrological and calendrical purposes
- Noticed stars rose earlier each night relative to the Sun's position
- Created star catalogs showing this gradual eastward drift
Greek astronomy (circa 600-300 BCE):
- Thales of Miletus (624-546 BCE): Used stellar observations for navigation
- Meton of Athens (432 BCE): Discovered the 19-year Metonic cycle, reconciling lunar months with solar years
- Recognized that stellar year differed from seasonal year
Hipparchus and Precession (150 BCE)
Hipparchus of Nicaea (circa 190-120 BCE), one of history's greatest astronomers:
Discovery: By comparing ancient Babylonian star catalogs with his own observations, Hipparchus discovered precession of the equinoxes—the slow westward drift of the vernal equinox against the stellar background
Sidereal measurements: To detect this subtle effect (1 degree per 72 years), Hipparchus needed precise sidereal positions, implicitly understanding the sidereal day concept
Legacy: His work established the difference between:
- Sidereal year: One orbit relative to stars (365.256363 days)
- Tropical year: One cycle of seasons (365.242199 days)
The ~20-minute difference between these years arises from precession.
Ptolemy's Almagest (150 CE)
Claudius Ptolemy compiled Greek astronomical knowledge in the Almagest, including:
- Star catalogs with sidereal positions
- Mathematical models for predicting stellar rising times
- Understanding that stars complete one full circuit of the sky slightly faster than the Sun
Though Ptolemy's geocentric model was wrong, his sidereal observations were accurate and useful for centuries.
Islamic Golden Age (800-1400 CE)
Islamic astronomers refined sidereal timekeeping:
Al-Battani (850-929 CE):
- Measured the tropical year to high precision
- Created improved star catalogs using sidereal positions
Ulugh Beg (1394-1449 CE):
- Built the Samarkand Observatory with advanced instruments
- Produced star catalogs accurate to ~1 arcminute using sidereal measurements
Copernican Revolution (1543)
Nicolaus Copernicus (De revolutionibus orbium coelestium, 1543):
Heliocentric model: Placing the Sun (not Earth) at the center explained the sidereal-solar day difference:
- Earth rotates on its axis (sidereal day)
- Earth orbits the Sun (creating solar day difference)
- The 4-minute discrepancy results from Earth's ~1° daily orbital motion
This was strong evidence for heliocentrism, though it took decades for acceptance.
Kepler's Laws (1609-1619)
Johannes Kepler formulated laws of planetary motion using sidereal periods:
Third Law: The square of a planet's orbital period is proportional to the cube of its orbit's semi-major axis
Application: Calculating planetary positions required precise sidereal reference frames, not solar time
Rise of Telescopic Astronomy (1600s-1700s)
Galileo Galilei (1609):
- Telescopic observations required tracking celestial objects as they moved across the sky
- Sidereal time became essential for predicting when objects would be visible
Royal Observatory, Greenwich (1675):
- Founded by King Charles II with John Flamsteed as first Astronomer Royal
- Developed accurate sidereal clocks to time stellar transits
- Greenwich Mean Sidereal Time (GMST) became the astronomical standard
Paris Observatory (1667):
- French astronomers developed precision pendulum clocks for sidereal timekeeping
- Cassini family produced detailed planetary observations using sidereal coordinates
Precision Timekeeping (1800s)
19th century: Mechanical sidereal clocks achieved second-level accuracy:
Sidereal clock design: Modified to tick 366.2422/365.2422 times faster than solar clocks (accounting for the extra sidereal day per year)
Observatory operations: Major observatories (Greenwich, Paris, Harvard, Lick, Yerkes) used sidereal clocks as primary timekeeping for scheduling observations
Photography: Long-exposure astrophotography required tracking objects at the sidereal rate to prevent star trailing
IAU Standardization (1900s)
International Astronomical Union (IAU) formalized definitions:
Mean sidereal day: 86,164.0905 seconds (exactly, by definition)
Greenwich Mean Sidereal Time (GMST): Standard sidereal time referenced to Greenwich meridian
Vernal equinox reference: Traditional sidereal time measures Earth's rotation relative to the vernal equinox (intersection of celestial equator and ecliptic)
Modern Era: ICRF (1997-Present)
International Celestial Reference Frame (ICRF):
Problem: The vernal equinox shifts due to precession, making it an imperfect reference
Solution: ICRF uses ~300 distant quasars (billions of light-years away) as fixed reference points
Accuracy: Defines celestial positions to milliarcsecond precision
Atomic time: Sidereal time is now calculated from International Atomic Time (TAI) and Earth orientation parameters measured by Very Long Baseline Interferometry (VLBI)
Modern sidereal clocks: Digital, GPS-synchronized, automatically updated for Earth rotation variations
Common Uses and Applications: minutes vs sidereal days
Explore the typical applications for both Minute (imperial/US) and Sidereal Day (imperial/US) to understand their common contexts.
Common Uses for minutes
and Applications
1. Time Management and Productivity
The minute is the fundamental unit for personal and professional time management:
- Pomodoro Technique: Work in 25-minute focused sessions, followed by 5-minute breaks
- Time blocking: Schedule day in 15-, 30-, or 60-minute blocks
- Task estimation: "This report will take 45 minutes"
- Billable hours: Professional services (lawyers, consultants) often bill in 6-minute increments (0.1 hour)
- Timesheet tracking: Many systems track work time to the minute
Digital tools: Calendar apps (Google Calendar, Outlook), time tracking software (Toggl, RescueTime), and project management platforms (Asana, Monday.com) all operate on minute-based scheduling.
2. Scheduling and Appointments
Minutes enable precise coordination of activities:
- Appointment times: "Dentist at 3:15 PM" (hours and minutes)
- Event start times: "Meeting begins at 10:30 AM sharp"
- Transit timetables: "Train departs at 8:47 AM"
- Reservation systems: OpenTable shows "5:30 PM" or "8:45 PM" slots
- Class schedules: "Period 3: 10:25-11:15 AM" (50-minute period)
Buffer times: Professional schedulers often include 5-10 minute buffers between appointments to prevent domino-effect delays.
3. Sports and Athletic Competition
Many sports use minutes for game structure and performance measurement:
-
Game periods:
- Soccer: Two 45-minute halves
- Basketball (NBA): Four 12-minute quarters = 48 minutes total
- Basketball (NCAA): Two 20-minute halves = 40 minutes
- Hockey: Three 20-minute periods
- Rugby: Two 40-minute halves
-
Penalties and suspensions:
- Hockey penalty box: 2-minute, 4-minute, or 5-minute penalties
- Soccer yellow card: 10-minute sin bin (trial rule in some leagues)
-
Running performance:
- Mile time: 4-6 minutes (recreational), under 4 minutes (elite)
- 5K time: 15-30 minutes (recreational), 13-15 minutes (competitive)
- Marathon pace: Expressed as minutes per mile/km
-
Timeouts:
- NBA timeout: 75 seconds (1.25 minutes) or 30 seconds
- NFL timeout: Each team gets three per half
- College football: 1-minute timeouts
4. Navigation and Geography
Beyond time measurement, "minute" has a distinct meaning in navigation:
Arcminute (minute of arc):
- Symbol: ′ (prime symbol)
- 1 arcminute = 1/60 of a degree of angle
- 1 degree = 60 arcminutes = 60′
- 1 arcminute = 60 arcseconds = 60″
Latitude and longitude:
- Geographic coordinates: 40°45′30″N, 73°59′00″W (New York City)
- Reads as: "40 degrees, 45 minutes, 30 seconds North; 73 degrees, 59 minutes, 0 seconds West"
Nautical mile:
- 1 nautical mile = 1 arcminute of latitude (approximately 1,852 meters)
- This makes ocean navigation calculations elegant: traveling 60 nautical miles north changes your latitude by 1 degree
Map precision:
- 1 arcminute of latitude ≈ 1.85 km (1.15 miles)
- 1 arcminute of longitude ≈ 1.85 km at equator (decreases toward poles)
- Modern GPS coordinates often express minutes with decimal precision: 40°45.5′N
5. Digital Timekeeping and Computing
Computers and digital devices track time in minutes (and smaller units):
- System clocks: Display hours:minutes (14:35) or hours:minutes:seconds (14:35:47)
- File timestamps: Modified time recorded as YYYY-MM-DD HH:MM:SS
- Cron jobs: Unix/Linux scheduled tasks use minute-level specification (0-59)
- Session timeouts: "Session will expire in 5 minutes of inactivity"
- Auto-save intervals: Microsoft Word auto-saves every 10 minutes (default)
- Video timestamps: YouTube shows 5:23 (5 minutes, 23 seconds)
- Countdown timers: Online cooking timers, exam clocks, auction endings
6. Aviation and Air Travel
The aviation industry relies heavily on minute-precise timing:
- Flight schedules: Departure 10:25 AM, arrival 1:47 PM (all times to the minute)
- Flight duration: "Flight time: 2 hours 34 minutes"
- Boarding times: "Boarding begins 30 minutes before departure"
- Gate changes: "Gate closes 10 minutes before departure"
- Air traffic control: Separation requirements measured in minutes between aircraft
- Fuel planning: Reserve fuel calculated for 30-45 minutes of additional flight time
7. Education and Testing
Academic settings structure learning and assessment by minutes:
-
Class periods:
- Elementary school: 45-60 minute periods
- High school: 50-minute periods (traditional) or 90-minute blocks
- University lecture: 50 minutes ("hour" classes), 80 minutes (longer sessions)
- "10-minute break" between classes
-
Standardized tests:
- SAT Reading section: 65 minutes
- SAT Math (calculator): 55 minutes
- ACT Science: 35 minutes
- GRE Verbal section: 30 minutes
- LSAT Logical Reasoning: 35 minutes per section
-
Test-taking strategy: Students allocate time per question (e.g., "100 questions in 60 minutes = 36 seconds per question")
8. Parking and Paid Time
Many services charge based on minute increments:
-
Parking meters:
- 15-minute minimum in some cities
- $2 per hour = $0.50 per 15 minutes
- Digital meters show minutes remaining
-
Bike/scooter sharing:
- Lime, Bird, Citibike: Charge per minute (e.g., $0.39/min)
- "Unlock fee + per-minute rate"
-
Phone plans (historical):
- Pre-smartphone era: Plans sold as "450 minutes per month"
- Long-distance charges: "5¢ per minute"
- Modern shift: Unlimited minutes, data caps instead
-
Professional services:
- Legal billing: Often in 6-minute increments (1/10 hour)
- Therapy sessions: 50-minute "hour" (allows 10 minutes for notes)
- Consulting rates: "$200/hour" = $3.33/minute
9. Emergency Services
Response time measured in minutes can mean life or death:
-
Response time targets:
- Ambulance (urban): 8 minutes average target
- Fire department: 4-minute turnout time (from alarm to truck departure)
- Police: Varies widely, 5-10 minutes for priority calls
-
Emergency medical guidelines:
- Start CPR within 1 minute of cardiac arrest recognition
- Defibrillation within 3-5 minutes of cardiac arrest improves survival
- Every 1-minute delay in defibrillation decreases survival by 7-10%
- "Time is tissue" in stroke care: Every minute counts
-
911 call processing:
- Average call duration: 2-3 minutes
- Location identification: Should be under 30 seconds
- "Stay on the line" until help arrives
When to Use sidereal days
1. Telescope Pointing and Tracking
Professional observatories use sidereal time to point telescopes:
Right Ascension (RA): Celestial equivalent of longitude, measured in hours of sidereal time (0h to 24h)
Local Sidereal Time (LST): The current RA crossing the meridian
Pointing formula: If LST = 18h 30m, objects with RA ≈ 18h 30m are currently at their highest point (zenith)
Tracking rate: Telescope motors rotate at the sidereal rate (1 rotation per 23h 56m 4s) to follow stars across the sky as Earth rotates
Example:
- Vega: RA = 18h 37m
- When LST = 18:37, Vega crosses the meridian (highest in sky)
- Observer can plan observations when object will be optimally placed
2. Astrophotography
Long-exposure astrophotography requires tracking at the sidereal rate:
Problem: Earth's rotation makes stars trail across the image during long exposures
Solution: Equatorial mounts with sidereal drive motors:
- Rotate at exactly 1 revolution per sidereal day
- Keep stars fixed in the camera's field of view
- Enables exposures of minutes to hours without star trailing
Adjustment: Solar rate ≠ sidereal rate; photographers must use sidereal tracking for stars, solar tracking for Sun/Moon
3. Satellite Orbit Planning
Satellite engineers use sidereal time for orbit design:
Sun-synchronous orbits: Satellites that always cross the equator at the same local solar time
- Orbital period is chosen to precess at the solar rate, not sidereal rate
Geosynchronous orbits: Satellites that hover over one point on Earth
- Orbital period = 1 sidereal day (23h 56m 4s)
- NOT 24 hours! Common misconception.
Molniya orbits: High-eccentricity orbits with period = 0.5 sidereal days for optimal high-latitude coverage
4. Very Long Baseline Interferometry (VLBI)
Radio astronomers use VLBI to achieve ultra-high resolution:
Technique: Combine signals from radio telescopes across continents
Timing requirement: Sidereal time must be synchronized to nanosecond precision across all telescopes
Result: VLBI can resolve features 1,000 times smaller than Hubble Space Telescope (angular resolution ~0.0001 arcseconds)
Application: Measures Earth's rotation variations by observing quasars at precise sidereal times
5. Navigation and Geodesy
Sidereal time is used for precise Earth orientation measurements:
Earth Orientation Parameters (EOPs):
- Polar motion (wobble of Earth's axis)
- UT1 (Earth rotation angle, related to Greenwich sidereal time)
- Length of day variations
GPS accuracy: GPS navigation requires knowing Earth's orientation to ~1 meter precision, necessitating sidereal time corrections
Tidal forces: Moon and Sun create tidal bulges that affect Earth's rotation, causing sidereal day variations at the millisecond level
6. Space Navigation
Spacecraft use sidereal reference frames:
Star trackers: Autonomous spacecraft orientation using star patterns
- Compare observed stellar positions with catalog
- Catalog uses sidereal coordinates (RA/Dec)
Interplanetary navigation: Voyager, New Horizons, and other deep-space probes navigate using sidereal reference frames (ICRF)
Mars rovers: Use Martian sidereal time ("sols") for mission planning
- 1 Mars sol = 24h 39m 35s (Mars rotates slower than Earth)
7. Amateur Astronomy
Amateur astronomers use sidereal time for planning:
Planispheres: Rotating star charts that show which constellations are visible at any given sidereal time and date
Computerized telescopes: GoTo mounts require accurate sidereal time for automatic star finding
Observation logs: Record sidereal time of observations for repeatability
Additional Unit Information
About Minute (min)
How many seconds are in a minute?
Exactly 60 seconds. This has been standardized since medieval times and is based on the Babylonian base-60 (sexagesimal) number system. Since 1967, when the second was redefined using atomic cesium-133 clocks, one minute equals precisely 60 atomic seconds, or 551,558,906,200 oscillations of caesium-133 radiation.
How many minutes are in an hour?
Exactly 60 minutes. This also comes from Babylonian mathematics. The hour was divided into 60 "first small parts" (Latin: pars minuta prima = minutes), just as each minute is divided into 60 "second small parts" (Latin: pars minuta secunda = seconds).
Why are there 60 minutes in an hour, not 100?
The base-60 system comes from ancient Babylonian mathematics (c. 3000 BCE). The Babylonians chose 60 because it's highly divisible—it has 12 factors (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60), making fractions much simpler:
- 1/2 hour = 30 min (whole number)
- 1/3 hour = 20 min (whole number)
- 1/4 hour = 15 min (whole number)
- 1/5 hour = 12 min (whole number)
- 1/6 hour = 10 min (whole number)
Contrast with 100 (decimal): 1/3 of 100 = 33.33... (repeating decimal). The Babylonians had sophisticated astronomy requiring complex divisions, so base-60 was superior.
How many minutes are in a day?
1,440 minutes in one 24-hour day.
Calculation: 24 hours × 60 minutes/hour = 1,440 minutes
Breakdown:
- 12 hours (half day) = 720 minutes
- 6 hours (quarter day) = 360 minutes
- 1 hour = 60 minutes
How many minutes are in a year?
525,600 minutes in a standard 365-day year.
Calculation: 365 days × 24 hours × 60 minutes = 525,600 minutes
This number was popularized by the opening song "Seasons of Love" from the 1996 Broadway musical Rent:
"Five hundred twenty-five thousand, six hundred minutes... How do you measure, measure a year?"
For a leap year (366 days): 527,040 minutes (1,440 more minutes).
What's the difference between a minute of time and an arcminute?
Time minute: A unit of duration equal to 60 seconds.
- Symbol: min (or sometimes just listed as "minutes")
- Used for measuring elapsed time, scheduling, etc.
Arcminute (minute of arc): A unit of angular measurement equal to 1/60 of a degree.
- Symbol: ′ (prime symbol)
- Used in astronomy, navigation, and geographic coordinates
- Example: 40°45′30″N = 40 degrees, 45 arcminutes, 30 arcseconds North latitude
Key connection: In navigation, 1 arcminute of latitude = 1 nautical mile (approximately 1,852 meters). This elegant relationship makes nautical charts and navigation calculations simpler.
Same name, different measurements:
- Both descend from the Latin pars minuta prima (first small part) referring to 1/60 divisions
- Context clarifies which is meant
How do I convert minutes to decimal hours?
Formula: Decimal hours = minutes ÷ 60
Examples:
- 30 minutes = 30 ÷ 60 = 0.5 hours
- 15 minutes = 15 ÷ 60 = 0.25 hours
- 45 minutes = 45 ÷ 60 = 0.75 hours
- 90 minutes = 90 ÷ 60 = 1.5 hours
- 20 minutes = 20 ÷ 60 = 0.333... hours (approximately 0.33)
Common conversions:
- 6 minutes = 0.1 hours (used in legal billing: 0.1 hour increments)
- 12 minutes = 0.2 hours
- 18 minutes = 0.3 hours
- 36 minutes = 0.6 hours
Reverse (decimal hours to minutes): Multiply decimal part by 60
- Example: 1.75 hours = 1 hour + (0.75 × 60) = 1 hour 45 minutes
How do I convert hours:minutes format to just minutes?
Formula: Total minutes = (hours × 60) + minutes
Examples:
- 1:30 (1 hour 30 min) = (1 × 60) + 30 = 90 minutes
- 2:15 (2 hours 15 min) = (2 × 60) + 15 = 135 minutes
- 0:45 (45 minutes) = (0 × 60) + 45 = 45 minutes
- 3:20 (3 hours 20 min) = (3 × 60) + 20 = 200 minutes
- 8:00 (8 hours) = (8 × 60) + 0 = 480 minutes (full work day)
This is useful for calculating total duration, comparing times, or doing time arithmetic.
When did clocks start showing minutes?
Early mechanical clocks (1300s-1650s) had only hour hands because they weren't accurate enough to justify showing minutes. Early clocks could lose or gain 15-30 minutes per day.
Minute hands appeared around 1670-1680, shortly after Christiaan Huygens invented the pendulum clock in 1656, which improved accuracy from ~15 minutes/day error to ~15 seconds/day error—a roughly 60× improvement.
Key timeline:
- 1656: Huygens invents pendulum clock
- 1657: First pendulum clocks built (with minute hands)
- 1670s: Minute hands become standard on quality clocks
- 1675: Balance spring invented (Huygens/Hooke), further improving accuracy
- 1680s: Pocket watches begin including minute hands
- 1700s: Minute display becomes universal
Before this, society didn't need minute-level precision—daily life organized around hours, bells, and approximate times. The pendulum clock created both the technical ability and social need for minute-based scheduling.
Do all countries use minutes the same way?
Yes—the 60-minute hour is universal worldwide. Unlike distance (metric vs. imperial) or temperature (Celsius vs. Fahrenheit), time measurement is globally standardized:
- All countries use 60 seconds per minute
- All countries use 60 minutes per hour
- All countries use 24 hours per day
International Standards:
- ISO 8601 (international date/time standard) uses HH:MM:SS format universally
- Coordinated Universal Time (UTC) is the global time standard
- All time zones are defined as offsets from UTC (e.g., EST = UTC-5, JST = UTC+9)
Cultural differences in time display (not measurement):
- 12-hour format (US, Canada, Australia, Philippines): 3:45 PM
- 24-hour format (most of world, military, aviation): 15:45
- Both systems use the same 60-minute hours—just different notation
Historical exception: During the French Revolution (1793-1805), France briefly tried decimal time with 100-minute hours, but it was abandoned as impractical.
How do stopwatches and timers measure fractions of a minute?
Stopwatches display time more precisely than minutes using minutes:seconds.deciseconds format:
Common formats:
- M:SS (minutes:seconds) — e.g., 3:45 = 3 minutes, 45 seconds
- M:SS.SS (minutes:seconds.centiseconds) — e.g., 3:45.23 = 3 min, 45.23 sec
- H:MM:SS (hours:minutes:seconds) — e.g., 1:23:45 = 1 hr, 23 min, 45 sec
Precision levels:
- Sport timing: Typically to 0.01 seconds (centiseconds)
- Olympic 100m: 9.58 seconds (Usain Bolt world record)
- Lab/scientific stopwatches: To 0.001 seconds (milliseconds)
- Atomic clocks: To nanoseconds (0.000000001 seconds) or better
Digital displays:
- Phone stopwatch: Usually shows minutes:seconds.centiseconds (3:45.67)
- Microwave timer: Usually shows minutes:seconds only (3:45)
- Oven timer: Minutes only for long cooking (45), or minutes:seconds for precise tasks
Fractions of minutes in speech:
- "Three and a half minutes" = 3:30
- "Two minutes thirty seconds" = 2:30
- "Five minutes fifteen seconds" = 5:15
Why do clocks go up to 60 minutes, not continue beyond?
At 60 minutes, the minute counter resets to 0 and the hour increments by 1. This is called modular arithmetic or "clock arithmetic":
- 0 minutes → 1 minute → ... → 59 minutes → 0 minutes (next hour)
- Example: 2:59 PM + 1 minute = 3:00 PM (not 2:60 PM)
Why?
- Babylonian base-60 system: We use 60 as the cycle
- Analog clock design: The minute hand makes one complete circle (360°) per hour, returning to 12
- Mathematical consistency: Just as we don't have 60 seconds (it becomes 1 minute), we don't have 60 minutes (it becomes 1 hour)
Modulo 60:
- In mathematics, this is written as minutes mod 60
- Adding times requires carrying: 45 min + 20 min = 65 min = 1 hr 5 min
- Computer timekeeping uses this logic internally
Exception: Elapsed time can exceed 60 minutes:
- "This meeting lasted 90 minutes" (1 hour 30 minutes)
- Marathon time: 2:15:30 (2 hours, 15 minutes, 30 seconds)
About Sidereal Day (sidereal day)
How long is a sidereal day in standard time?
Answer: 23 hours, 56 minutes, 4.091 seconds (or 86,164.091 seconds)
This is the time for Earth to rotate exactly 360 degrees relative to distant stars.
Precise value: 1 mean sidereal day = 86,164.0905 seconds
Comparison to solar day:
- Solar day: 86,400 seconds (24 hours)
- Sidereal day: 86,164.091 seconds
- Difference: ~236 seconds shorter (~3 min 56 sec)
Important: This is the mean sidereal day. Earth's actual rotation rate varies slightly (milliseconds) due to tidal forces, atmospheric winds, earthquakes, and core-mantle coupling.
Why is a sidereal day shorter than a solar day?
Answer: Because Earth orbits the Sun while rotating—requiring extra rotation to bring the Sun back to the same sky position
Step-by-step explanation:
-
Starting point: The Sun is directly overhead (noon)
-
One sidereal day later (23h 56m 4s): Earth has rotated exactly 360° relative to stars
- But Earth has also moved ~1° along its orbit around the Sun
- The Sun now appears slightly east of overhead
-
Extra rotation needed: Earth must rotate an additional ~1° (taking ~4 minutes) to bring the Sun back overhead
-
Result: Solar day (noon to noon) = sidereal day + ~4 minutes = 24 hours
Orbital motion causes the difference: Earth moves ~1°/day along its 365-day orbit (360°/365 ≈ 0.986°/day). This ~1° requires ~4 minutes of extra rotation (24 hours / 360° ≈ 4 min/degree).
Consequence: Stars rise ~4 minutes earlier each night relative to solar time, shifting ~2 hours per month, completing a full cycle annually.
Is sidereal time the same everywhere on Earth?
Answer: No—Local Sidereal Time (LST) depends on longitude, just like solar time zones
Key concepts:
Local Sidereal Time (LST): The Right Ascension (RA) currently crossing your local meridian
- Different at every longitude
- Changes by 4 minutes for every 1° of longitude
Greenwich Mean Sidereal Time (GMST): Sidereal time at 0° longitude (Greenwich meridian)
- Global reference point, like GMT/UTC for solar time
Conversion: LST = GMST ± longitude offset
- Positive (add) for east longitudes
- Negative (subtract) for west longitudes
Example:
- GMST = 12:00
- New York (74°W): LST = 12:00 - (74°/15) = 07:04
- Tokyo (139.75°E): LST = 12:00 + (139.75°/15) = 21:19
Duration is universal: A sidereal day (23h 56m 4s) is the same length everywhere—only the current sidereal time differs by location.
Do geosynchronous satellites orbit every 24 hours or 23h 56m?
Answer: 23h 56m 4s (one sidereal day)—NOT 24 hours!
This is one of the most common misconceptions about satellites.
The physics: For a satellite to remain above the same point on Earth's surface, it must orbit at Earth's rotational rate relative to the stars, not relative to the Sun.
Why sidereal?
- Earth rotates 360° in one sidereal day (23h 56m 4s)
- Satellite must complete 360° orbit in the same time
- This keeps satellite and ground point aligned relative to the stellar background
If orbit were 24 hours: The satellite would complete one orbit in one solar day, but Earth would have rotated 360° + ~1° (relative to stars) during that time. The satellite would drift ~1° westward per day, completing a full circuit westward in one year!
Geostationary orbit specifics:
- Altitude: 35,786 km above equator
- Period: 23h 56m 4.091s (1 sidereal day)
- Velocity: 3.075 km/s
Common examples: Communications satellites, weather satellites (GOES, Meteosat)
How many sidereal days are in a year?
Answer: Approximately 366.25 sidereal days—one MORE than the number of solar days!
Precise values:
- Tropical year (season to season): 365.242199 mean solar days
- Sidereal year (star to star): 365.256363 mean solar days
- Sidereal days in tropical year: 366.242199 sidereal days
One extra day: There is exactly one more complete rotation relative to stars than we experience sunrises.
Why?
- Earth makes 366.25 complete 360° rotations relative to stars per year
- But we experience only 365.25 sunrises because we orbit the Sun
- One rotation is "used up" by Earth's orbit around the Sun
Thought experiment: Stand on a rotating platform while walking around a lamp. If you walk one complete circle around the lamp (1 orbit), you'll have spun around 2 complete times relative to the room walls (2 rotations): 1 from walking the circle + 1 from the platform spinning.
Can I use a regular clock to tell sidereal time?
Answer: Not directly—sidereal clocks run about 4 minutes faster per day than solar clocks
Clock rate difference:
- Solar clock: Completes 24 hours in 1 solar day (86,400 seconds)
- Sidereal clock: Completes 24 sidereal hours in 1 sidereal day (86,164.091 seconds)
- Rate ratio: 1.00273791 (sidereal clock ticks ~0.27% faster)
Practical result: After one solar day:
- Solar clock reads: 24:00
- Sidereal clock reads: 24:03:56 (3 min 56 sec ahead)
Modern solutions:
- Sidereal clock apps: Smartphone apps calculate LST from GPS location and atomic time
- Planetarium software: Stellarium, SkySafari show current LST
- Observatory systems: Automated telescopes use GPS-synchronized sidereal clocks
Historical: Mechanical sidereal clocks used gear ratios of 366.2422/365.2422 to run at the correct rate
You can calculate: LST from solar time using formulas, but it's complex (requires Julian Date, orbital mechanics)
Why do astronomers use sidereal time instead of solar time?
Answer: Because celestial objects return to the same position every sidereal day, not solar day
Astronomical reason:
Stars and galaxies are so distant they appear "fixed" in the sky:
- A star at RA = 18h 30m crosses the meridian at LST = 18:30 every sidereal day
- Predictable, repeatable observations
If using solar time: Stars would cross the meridian ~4 minutes earlier each night, requiring daily recalculation of observation windows
Practical advantages:
1. Simple telescope pointing:
- Object's RA directly tells you when it's overhead (LST = RA)
- No date-dependent calculations needed
2. Repeatable observations:
- "Observe target at LST = 22:00" means the same sky position regardless of date
3. Right Ascension coordinate system:
- Celestial longitude measured in hours/minutes of sidereal time (0h to 24h)
- Aligns naturally with Earth's rotation
4. Tracking rate:
- Telescopes track at sidereal rate (1 revolution per 23h 56m 4s)
- Keeps stars fixed in the field of view
Historical: Before computers, sidereal time made astronomical calculations much simpler
What is the difference between a sidereal day and a sidereal year?
Answer: A sidereal day measures Earth's rotation; a sidereal year measures Earth's orbit
Sidereal Day:
- Definition: Time for Earth to rotate 360° on its axis relative to stars
- Duration: 23h 56m 4.091s (86,164.091 seconds)
- Reference: Distant "fixed" stars
- Use: Telescope tracking, astronomy observations
Sidereal Year:
- Definition: Time for Earth to orbit 360° around the Sun relative to stars
- Duration: 365.256363 days (365d 6h 9m 9s)
- Reference: Position relative to distant stars (not seasons)
- Use: Orbital mechanics, planetary astronomy
Key distinction:
- Day = rotation (Earth spinning)
- Year = revolution (Earth orbiting)
Tropical vs. Sidereal Year:
- Tropical year: 365.242199 days (season to season, used for calendars)
- Sidereal year: 365.256363 days (star to star)
- Difference: ~20 minutes, caused by precession of Earth's axis
The 20-minute precession effect: Earth's axis wobbles with a 26,000-year period, causing the vernal equinox to shift ~50 arcseconds/year westward against the stellar background. This makes the tropical year (equinox to equinox) slightly shorter than the sidereal year (star to star).
Does the Moon have a sidereal day?
Answer: Yes—the Moon's sidereal day is 27.322 Earth days, but it's tidally locked to Earth
Moon's sidereal rotation: Time for Moon to rotate 360° relative to stars = 27.322 days
Tidal locking: The Moon's rotation period equals its orbital period around Earth (both 27.322 days)
Consequence: The same face of the Moon always points toward Earth
- We only see ~59% of Moon's surface from Earth (libration allows slight wobbling)
- The "far side" never faces Earth
Moon's "solar day" (lunar day):
- Time from sunrise to sunrise on Moon's surface: 29.531 Earth days
- Different from Moon's sidereal day (27.322 days) for the same reason Earth's solar day differs from sidereal day
- Moon orbits Earth while rotating, requiring extra rotation to bring the Sun back to the same position
Lunar missions: Apollo missions and rovers used "lunar days" for mission planning—each day-night cycle lasts ~29.5 Earth days (2 weeks daylight, 2 weeks night)
How is sidereal time measured today?
Answer: Using atomic clocks, GPS, and Very Long Baseline Interferometry (VLBI) observations of distant quasars
Modern measurement system:
1. International Atomic Time (TAI):
- Network of ~450 atomic clocks worldwide
- Defines the second with nanosecond precision
- Provides base timescale
2. UT1 (Universal Time):
- Earth's rotation angle (actual rotation measured continuously)
- Monitored by VLBI observations of quasars
3. VLBI technique:
- Radio telescopes across continents simultaneously observe distant quasars
- Time differences reveal Earth's exact orientation
- Accuracy: ~0.1 milliseconds (0.005 arcseconds rotation)
4. ICRF (International Celestial Reference Frame):
- Defines "fixed" stellar background using ~300 quasars billions of light-years away
- Replaces older vernal equinox reference (which shifts due to precession)
5. GPS satellites:
- Amateur astronomers and observatories use GPS for accurate time and location
- Software calculates LST from UTC, GPS coordinates, and Earth orientation parameters
Calculation chain:
- Atomic clocks provide UTC
- Earth orientation parameters (EOP) give UT1
- Sidereal time formulas convert UT1 → GMST
- Longitude correction gives LST
Accuracy: Modern systems know Earth's orientation to ~1 centimeter (as a position on Earth's surface), requiring sidereal time precision of ~0.001 seconds
Why so complex? Earth's rotation is not uniform:
- Tidal forces (Moon/Sun) slow rotation by ~2.3 ms/century
- Atmospheric winds cause daily variations (milliseconds)
- Earthquakes can shift rotation by microseconds
- Core-mantle coupling affects long-term drift
Continuous monitoring ensures astronomical observations remain accurate.
Will sidereal time ever be replaced by something else?
Answer: Unlikely—it's fundamental to astronomy, tied directly to Earth's rotation and stellar positions
Why sidereal time persists:
1. Physical basis: Directly tied to Earth's rotation relative to the universe
- Not an arbitrary human convention like time zones
- Essential for understanding celestial mechanics
2. Coordinate system: Right Ascension (celestial longitude) is measured in sidereal hours
- All star catalogs, telescope systems, and astronomical databases use RA/Dec
- Replacing it would require re-cataloging billions of objects
3. Telescope tracking: All telescope mounts track at the sidereal rate
- Mechanically and electronically built into equipment
- Solar tracking is used only for Sun/Moon
4. International standards: IAU, observatories, space agencies globally use sidereal time
- Standardized formulas and software
5. No alternative needed: Sidereal time does its job perfectly for astronomy
Evolution, not replacement:
- Old reference: Vernal equinox (shifts due to precession)
- New reference: ICRF quasars (effectively fixed)
- Future: Increasingly precise atomic timescales and Earth rotation monitoring
Non-astronomical contexts: Civil society will continue using solar time (UTC) for daily life—there's no need for most people to know sidereal time
Conclusion: Sidereal time is here to stay as long as humans do astronomy from Earth. Even space-based observatories use sidereal coordinate systems for consistency with ground observations.
Conversion Table: Minute to Sidereal Day
| Minute (min) | Sidereal Day (sidereal day) |
|---|---|
| 0.5 | 0 |
| 1 | 0.001 |
| 1.5 | 0.001 |
| 2 | 0.001 |
| 5 | 0.004 |
| 10 | 0.007 |
| 25 | 0.017 |
| 50 | 0.035 |
| 100 | 0.07 |
| 250 | 0.174 |
| 500 | 0.348 |
| 1,000 | 0.696 |
People Also Ask
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Learn more →What are common uses for Minute and Sidereal Day?
Minute and Sidereal Day are both standard units used in time measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our time converter for more conversion options.
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- Decade (dec) • Minute to Decade
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Last verified: December 3, 2025