About TimeSmith
A precision instrument for exploring time across calendar systems—how humanity has measured, understood, and organized the passage of days throughout history.
The Concept
Time Dial is a museum-quality interactive visualization that lets you explore how a single moment in time is represented across multiple calendar systems simultaneously. By spinning the dial, you travel through time and see how dates align across Gregorian, Mayan, Lunar, and world time zones.
The canonical source of truth is the Julian Day Number (JDN)—a continuous count of days used by astronomers since 4713 BCE. All other calendars are deterministically computed from this single value, ensuring perfect synchronization across systems.
Julian Day Number (JDN)
The universal time coordinate
How It Was Created
The Julian Day system was devised in 1583 by Joseph Justus Scaliger, a French scholar who named it after his father Julius Caesar Scaliger (not Julius Caesar the Roman). Scaliger needed a way to correlate dates across different calendars used throughout history without negative numbers or year-zero confusion.
Who Uses It
Astronomers universally use JDN to timestamp celestial observations, avoiding calendar reform complications. Historians use it to convert between ancient calendars. Software engineers use it as a reference epoch for date calculations.
How It Works
JDN counts consecutive days from a starting epoch: January 1, 4713 BCE (Julian calendar) at noon Universal Time. This date was chosen because it's before any historical record and is the convergence of three cycles: the 28-year solar cycle, 19-year Metonic cycle, and 15-year indiction cycle.
Accuracy: Exact. The JDN is the foundation for all other calendar conversions in Time Dial.
Gregorian Calendar
The international civil standard
How It Was Created
Introduced on October 15, 1582 by Pope Gregory XIII, the Gregorian calendar reformed the Julian calendar to correct its accumulated 10-day drift. The Julian calendar's leap year rule (every 4 years) was too generous—the actual solar year is 365.2422 days, not 365.25. Gregory's astronomers devised a new rule: skip century years unless divisible by 400.
Who Used It & When
Catholic countries adopted it immediately in 1582. Protestant nations resisted for centuries—Britain and its colonies didn't switch until 1752, Russia until 1918, and Greece until 1923. Today, it's the de facto global standard for civil use, though many cultures maintain parallel traditional calendars.
Why It Was Needed
Easter was drifting away from its intended springtime date. The Council of Nicaea (325 CE) had tied Easter to the spring equinox, but by the 16th century, the Julian calendar's accumulated error had shifted the equinox from March 21 to March 11. The Church needed to restore the astronomical alignment of its most important holy day.
How It Works
12 months of 28-31 days each, totaling 365 days in a common year. Leap years add February 29. A year is a leap year if divisible by 4, except century years must be divisible by 400. Thus 2000 was a leap year, but 1900 was not. This gives an average year of 365.2425 days—accurate to within 1 day per 3,236 years.
What's Unique
The Gregorian calendar is purely solar—it tracks Earth's orbit around the Sun with no reference to lunar phases. It's also proleptic in Time Dial, meaning we extend it backwards before 1582 for convenience, though those dates are hypothetical.
Accuracy: Deterministic. Exact conversion from JDN using the Meeus algorithm.
Lunar Phase Calendar
The synodic rhythm of Earth's companion
History of Lunar Timekeeping
The Moon was humanity's first clock. Archaeological evidence shows lunar notation as early as 30,000 BCE. The synodic month—new moon to new moon—became the basis for the "month" itself (from Old English "mōnaþ," meaning Moon). Ancient Babylonians, Jews, Muslims, Chinese, and Hindus all developed lunar or lunisolar calendars.
Who Uses It Today
The Islamic calendar (Hijri) is purely lunar, used by 1.8 billion Muslims for religious observances. The Jewish and Chinese calendars are lunisolar—months track the Moon but years track the Sun via intercalary months. Farmers, fishers, and tidal planners still reference lunar phases for planting, harvesting, and navigation.
Why Track the Moon?
The Moon's phases are Earth's most visible celestial rhythm—impossible to ignore, easy to observe, and universally shared. Before artificial lighting, the full moon determined when nighttime travel and work were possible. Tides, menstrual cycles, and animal behaviors correlate with lunar phases. Many religious and cultural festivals are tied to specific Moon phases.
How It Works
The Moon orbits Earth in 27.3 days (sidereal month), but because Earth is also moving around the Sun, it takes 29.53 days for the Moon to return to the same phase (synodic month). Time Dial calculates the Moon's age (days since new moon), phase name, and illumination percentage using the Meeus algorithm referenced to the J2000.0 epoch.
Accuracy: Approximate (Meeus-style calculation). Sufficient for visual purposes but may differ by hours from precise NASA ephemeris data.
Mayan Calendar System
Mesoamerica's sophisticated interlocking cycles
How It Was Created
Developed by the Maya civilization over 2,000 years ago in Mesoamerica (present-day Mexico, Guatemala, Belize, Honduras). The system evolved from earlier Olmec and Zapotec calendars. Maya priests-astronomers observed celestial cycles with remarkable precision, creating a calendar that tracked Venus, eclipses, and astronomical conjunctions across millennia.
Who Used It
Used by the Maya, Aztec, and other Mesoamerican peoples from ~5th century BCE until Spanish colonization. The Long Count fell out of use by the 10th century CE, but the Tzolk'in and Haab' continue to be used by Maya communities in Guatemala and Mexico today—an unbroken tradition spanning over two millennia.
Why This System?
The Maya needed to track agricultural cycles, prophecy, dynastic history, and astronomical events. Their vigesimal (base-20) number system and concept of zero allowed them to record dates millions of years into the past and future. The calendar was central to religious ritual, political legitimacy, and everyday life.
Long Count (Linear Dating)
A continuous count of days since the mythological creation date—August 11, 3114 BCE in the GMT correlation. Written as a series of cycles: baktun.katun.tun.uinal.kin
The famous "end date" of December 21, 2012 was simply 13.0.0.0.0—the completion of 13 baktuns, not a prediction of doom, but a major calendar milestone like our Y2K.
Tzolk'in (260-Day Sacred Calendar)
The sacred almanac combining 13 numbers (1-13) with 20 day names (Imix, Ik, Akbal, etc.). Each day has a unique number-name combination that repeats every 260 days. Used for divination, ritual timing, and naming children—your birth day determined your destiny.
The 260-day cycle may derive from the human gestation period (~266 days), the interval between zenithal Sun passages at certain Maya latitudes, or astronomical cycles.
Haab' (365-Day Civil Calendar)
The "vague year" solar calendar with 18 named months of 20 days each, plus a 5-day period called Wayeb' (considered unlucky). Unlike our leap year system, the Haab' has no correction—it drifts ~1 day every 4 years relative to the true solar year.
Combined with the Tzolk'in, each date occurs once every 52 Haab' years (18,980 days)— the "Calendar Round," a complete cycle of all possible Tzolk'in-Haab' combinations.
Accuracy: Deterministic using the GMT correlation constant (584283). This can be adjusted in Settings to explore alternative correlations proposed by scholars.
World Time Zones
Standardizing the clock across a spinning planet
How They Were Created
Before railroads, every town set its clocks to local solar noon—Boston was 12 minutes ahead of New York. The chaos of hundreds of local times made rail schedules impossible. In 1883, US railroads adopted four standard time zones. In 1884, the International Meridian Conference established Greenwich, England as the prime meridian (0° longitude) and divided Earth into 24 hourly zones.
Global Adoption
Most nations adopted standard time zones by the early 20th century. Notable exceptions persist: China uses a single timezone despite spanning 5 geographical zones; Nepal is UTC+5:45; India is UTC+5:30. Daylight Saving Time, introduced during WWI to save fuel, remains controversial—many regions have abandoned it.
Why Standardize Time?
Modern civilization requires coordination. Stock markets, airline schedules, international calls, satellite links, and internet protocols all depend on synchronized clocks. The International Space Station crosses 16 time zones every orbit—it uses UTC exclusively. GPS satellites carry atomic clocks accurate to nanoseconds.
How Time Dial Handles Zones
Time Dial uses fixed UTC offsets (like UTC-7 for MST) rather than IANA timezone rules (like "America/Denver"). This is intentional: historical dates existed before DST was invented, and future dates may occur after a region abolishes DST. Fixed offsets ensure deterministic behavior across all time periods.
Date Line Crossings
When it's Monday evening in Tokyo (UTC+9), it's still Monday morning in New York (UTC-5). Time Dial shows these day boundaries with indicators. At UTC midnight, some zones are "tomorrow" while others are "yesterday"—a reminder that dates are local conventions.
Accuracy: Deterministic for fixed UTC offsets. Does not model historical timezone changes or DST transitions.
Technical Implementation
All date mathematics is performed client-side with no external API dependencies. Calculations are deterministic and reproducible.
- JDN ↔ Gregorian: Meeus algorithm (proleptic Gregorian)
- Mayan Long Count: GMT correlation constant (584283), configurable
- Tzolk'in / Haab': Modular arithmetic from Long Count
- Lunar Phases: Synodic month approximation from J2000.0 reference
- Animation: Framer Motion with momentum physics
- Stack: Next.js 15, React 19, TypeScript, Tailwind CSS, Zustand
Verification Resources
Cross-reference with authoritative sources