Time Converter
From Attoseconds to Eons: Mastering Time Units
Understand how time is measured — from atomic seconds and civil clocks to astronomical cycles and geological ages. Learn the caveats around months/years, leap seconds, and specialized scientific units.
Foundations of Timekeeping
Atomic definition
Modern seconds are realized by atomic clocks based on cesium transitions.
This provides globally consistent time independent of astronomical irregularities.
- TAI: International Atomic Time (continuous)
- UTC: Coordinated Universal Time (TAI adjusted by leap seconds)
- GPS time: like TAI (no leap seconds), offset from UTC
Civil Time & Zones
Civil clocks follow UTC but are offset by time zones and sometimes shifted by daylight saving time (DST).
Calendars define months and years — these are not fixed multiples of seconds.
- Months vary by calendar (we use a conventional average when converting)
- DST adds/removes 1 hour locally (no effect on UTC)
Astronomical Reality
Earth's rotation is irregular. Sidereal time (relative to stars) differs from solar time (relative to the Sun).
Astronomical cycles (synodic/sidereal months, tropical/sidereal years) are close but not identical.
- Solar day ≈ 86,400 s; sidereal day ≈ 86,164.09 s
- Synodic month ≈ 29.53 days; sidereal month ≈ 27.32 days
- Tropical year ≈ 365.24219 days
- Seconds are atomic; months/years are conventional
- UTC = TAI with leap seconds to track Earth's rotation
- Always clarify whether a 'year' or 'month' is tropical/sidereal/average
- Leap seconds are added to UTC to keep it aligned with Earth's rotation
Systems and Caveats
Atomic vs Astronomical
Atomic time is uniform; astronomical time reflects real‑world rotation/orbit variations.
- Use atomic seconds for conversions
- Map astronomical cycles to seconds with established constants
Calendars & Averages
Calendar months and years are not constant; converters use conventional averages unless stated.
- Average month ≈ 30.44 days
- Tropical year ≈ 365.24219 days
Leap Seconds & Offsets
UTC occasionally inserts a leap second; TAI and GPS do not.
- TAI − UTC varies (current offset depends on epoch)
- Conversions in seconds are unaffected by time zones/DST
Leap seconds and time scales (UTC/TAI/GPS)
| Time scale | Basis | Leap seconds | Relationship | Notes |
|---|---|---|---|---|
| UTC | Atomic seconds | Yes (inserted occasionally) | UTC = TAI − offset | Civil standard; aligns with Earth rotation via leap seconds |
| TAI | Atomic seconds | No | Continuous; TAI − UTC = N seconds (epoch‑dependent) | Reference continuous timescale for metrology |
| GPS | Atomic seconds | No | GPS = TAI − 19 s; GPS − UTC = N − 19 s | Used by GNSS; fixed offset to TAI, epoch‑dependent offset to UTC |
Civil Time & Calendars
Civil timekeeping layers time zones and calendars on top of UTC. Months and years are conventional, not exact multiples of seconds.
- Time zones are offsets from UTC (±hh:mm)
- DST shifts local clocks by +/−1 hour seasonally
- Average Gregorian month ≈ 30.44 days; not constant
Astronomical Time
Astronomy distinguishes sidereal (star‑based) from solar (Sun‑based) time; lunar and annual cycles have multiple definitions.
- Sidereal day ≈ 23h 56m 4.0905s
- Synodic vs sidereal month differ by Earth–Moon–Sun geometry
- Tropical vs sidereal vs anomalistic years
Geological Time
Geology spans millions to billions of years. Converters express these in seconds using scientific notation.
- Myr = million years; Gyr = billion years
- Ages, epochs, periods, eras, eons are relative geological scales
Historical & Cultural Time
- Olympiad (4 years, ancient Greece)
- Lustrum (5 years, ancient Rome)
- Mayan baktun/katun/tun cycles
Scientific & Specialized Units
Physics, computing, and legacy scholarly systems define special units for convenience or tradition.
- Jiffy, shake, svedberg (physics)
- Helek/rega (traditional), kè (Chinese)
- ‘Beat’ (Swatch Internet Time)
Planck Scale
Planck time tₚ ≈ 5.39×10⁻⁴⁴ s is derived from fundamental constants; relevant in quantum gravity theories.
- tₚ = √(ħG/c⁵)
- Orders of magnitude beyond experimental access
How Conversions Work
- min → s: × 60; h → s: × 3,600; d → s: × 86,400
- mo uses 30.44 days unless a specific calendar month is provided
- yr uses tropical year ≈ 365.24219 days by default
Quick Examples
Everyday Time Benchmarks
| Event | Duration | Context |
|---|---|---|
| Blink of an eye | 100-400 ms | Human perception threshold |
| Heartbeat (resting) | ~1 s | 60 beats per minute |
| Microwave popcorn | ~3 min | Quick snack preparation |
| TV episode (no ads) | ~22 min | Sitcom length |
| Movie | ~2 h | Feature film average |
| Full-time work day | 8 h | Standard shift |
| Human gestation | ~280 days | 9 months pregnancy |
| Earth orbit (year) | 365.24 days | Tropical year |
| Human Lifespan | ~80 years | 2.5 billion seconds |
| Recorded history | ~5,000 years | Writing to present |
Units Catalog
Metric / SI
| Unit | Symbol | Seconds | Notes |
|---|---|---|---|
| millisecond | ms | 0.001 | 1/1,000 of a second. |
| second | s | 1 | SI base unit; atomic definition. |
| attosecond | as | 1.000e-18 | Attosecond; attosecond spectroscopy. |
| femtosecond | fs | 1.000e-15 | Femtosecond; chemical dynamics. |
| microsecond | µs | 0.000001 | Microsecond; 1/1,000,000 s. |
| nanosecond | ns | 0.000000001 | Nanosecond; high‑speed electronics. |
| picosecond | ps | 1.000e-12 | Picosecond; ultrafast optics. |
| yoctosecond | ys | 1.000e-24 | Yoctosecond; theoretical scales. |
| zeptosecond | zs | 1.000e-21 | Zeptosecond; extreme physics. |
Common Time Units
| Unit | Symbol | Seconds | Notes |
|---|---|---|---|
| day | d | 86,400 | 86,400 seconds (solar day). |
| hour | h | 3,600 | 3,600 seconds. |
| minute | min | 60 | 60 seconds. |
| week | wk | 604,800 | 7 days. |
| year | yr | 31,557,600 | Tropical year ≈ 365.24219 days. |
| century | cent | 3.156e+9 | 100 years. |
| decade | dec | 315,576,000 | 10 years. |
| fortnight | fn | 1,209,600 | Fortnight = 14 days. |
| millennium | mill | 3.156e+10 | 1,000 years. |
| month | mo | 2,629,800 | Average calendar month ≈ 30.44 days. |
Astronomical Time
| Unit | Symbol | Seconds | Notes |
|---|---|---|---|
| anomalistic year | anom yr | 31,558,400 | Anomalistic year ≈ 365.25964 days. |
| eclipse year | ecl yr | 29,948,000 | Eclipse year ≈ 346.62 days. |
| galactic year | gal yr | 7.100e+15 | Sun’s orbit of the galaxy (order 2×10⁸ years). |
| lunar day | LD | 2,551,440 | ≈ 29.53 days. |
| saros (eclipse cycle) | saros | 568,025,000 | ≈ 18 years 11 days; eclipse cycle. |
| sidereal day | sid day | 86,164.1 | Sidereal day ≈ 86,164.09 s. |
| sidereal hour | sid h | 3,590.17 | Sidereal hour (1/24 of a sidereal day). |
| sidereal minute | sid min | 59.8362 | Sidereal minute. |
| sidereal month | sid mo | 2,360,590 | Sidereal month ≈ 27.32 days. |
| sidereal second | sid s | 0.99727 | Sidereal second. |
| sidereal year | sid yr | 31,558,100 | Sidereal year ≈ 365.25636 days. |
| sol (Martian day) | sol | 88,775.2 | Mars sol ≈ 88,775.244 s. |
| solar day | sol day | 86,400 | Solar day; civil baseline. |
| synodic month | syn mo | 2,551,440 | Synodic month ≈ 29.53 days. |
| tropical year | trop yr | 31,556,900 | Tropical year ≈ 365.24219 days. |
Geological Time
| Unit | Symbol | Seconds | Notes |
|---|---|---|---|
| billion years | Gyr | 3.156e+16 | Billion years (10⁹ years). |
| geological age | age | 3.156e+13 | Geological age (approximate). |
| geological eon | eon | 3.156e+16 | Geological eon. |
| geological epoch | epoch | 1.578e+14 | Geological epoch. |
| geological era | era | 1.262e+15 | Geological era. |
| geological period | period | 6.312e+14 | Geological period. |
| million years | Myr | 3.156e+13 | Million years (10⁶ years). |
Historical / Cultural
| Unit | Symbol | Seconds | Notes |
|---|---|---|---|
| baktun (Mayan) | baktun | 1.261e+10 | Mayan long count. |
| bell (nautical) | bell | 1,800 | Ship bell (30 minutes). |
| Callippic cycle | callippic | 2.397e+9 | Callippic cycle ≈ 76 years. |
| dog watch | dogwatch | 7,200 | Half watch (2 hours). |
| Hipparchic cycle | hip | 9.593e+9 | Hipparchic cycle ≈ 304 years. |
| indiction | indiction | 473,364,000 | 15‑year Roman tax cycle. |
| jubilee | jubilee | 1.578e+9 | Biblical 50‑year cycle. |
| katun (Mayan) | katun | 630,720,000 | Mayan 20‑year cycle. |
| lustrum | lustrum | 157,788,000 | 5 years (Roman). |
| Metonic cycle | metonic | 599,184,000 | Metonic cycle ≈ 19 years. |
| olympiad | olympiad | 126,230,000 | 4 years (ancient Greece). |
| tun (Mayan) | tun | 31,536,000 | Mayan 360‑day year. |
| watch (nautical) | watch | 14,400 | Nautical watch (4 hours). |
Scientific
| Unit | Symbol | Seconds | Notes |
|---|---|---|---|
| beat (Swatch Internet Time) | beat | 86.4 | Swatch Internet Time; day divided into 1,000 beats. |
| helek (Hebrew) | helek | 3.33333 | 3⅓ s (Hebrew). |
| jiffy (computing) | jiffy | 0.01 | Computing ‘jiffy’ (platform‑dependent, here 0.01 s). |
| jiffy (physics) | jiffy | 3.000e-24 | Physics jiffy ≈ 3×10⁻²⁴ s. |
| kè (刻 Chinese) | 刻 | 900 | kè 刻 ≈ 900 s (traditional Chinese). |
| moment (medieval) | moment | 90 | ≈ 90 s (medieval). |
| rega (Hebrew) | rega | 0.0444444 | ≈ 0.0444 s (Hebrew, traditional). |
| shake | shake | 0.00000001 | 10⁻⁸ s; nuclear engineering. |
| svedberg | S | 1.000e-13 | 10⁻¹³ s; sedimentation. |
| tau (half-life) | τ | 1 | Time constant; 1 s here as a reference. |
Planck Scale
| Unit | Symbol | Seconds | Notes |
|---|---|---|---|
| Planck time | tₚ | 5.391e-44 | tₚ ≈ 5.39×10⁻⁴⁴ s. |
Frequently Asked Questions
Why do month/year conversions look 'approximate'?
Because months and years are conventional. We use average values (month ≈ 30.44 d, tropical year ≈ 365.24219 d) unless specified otherwise.
UTC vs TAI vs GPS — which should I use?
For pure unit conversion, use seconds (atomic). UTC adds leap seconds; TAI and GPS are continuous and differ from UTC by a fixed offset for a given epoch.
Does DST affect conversions?
No. DST shifts wall clocks locally. Conversions between time units are based on seconds and are time‑zone agnostic.
What's a sidereal day?
The rotation period of Earth relative to distant stars, ≈ 86,164.09 seconds, shorter than the solar day of 86,400 seconds.
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