One phase instant rotates through three local nights and datesLive current inputs
Date & Time
Moon Phase Date Time-Zone Comparison Calculator
Compare one modeled lunar phase instant across three fixed-offset locations, identify local-date rollover, and estimate whether the event falls inside each entered nighttime observation window.
Modeled phase UTC instant—
Location A local label—
Location B local label—
Location C local label—
Local calendar-date spread—
Locations inside night window—
Widest local-clock separation—
Cross-zone comparison—
Global lunar-event window orbit
One phase instant rotates through three local nights and dates
A central phase disc anchors three local clock orbits. Night arcs reveal which locations receive the event inside the configured darkness proxy and which cross a civil-date boundary.
Local event comparison
Fixed-offset local labels and modeled night-window states
The night window is a time-of-day proxy around local midnight, not an astronomical darkness or visibility calculation.
| Location | UTC offset | Local date | Local time | Date relative to UTC | Night-window state |
|---|
Location comparison setup
Use one event and three explicit local contexts
- Enter the date from which to search for the next phase.
- Choose the same phase for all locations.
- Resolve each fixed UTC offset for the event date.
- Set a night-time proxy around local midnight.
- Treat visibility and darkness as separate location-specific questions.
Global instant logic
The lunar phase is shared; the calendar and clock labels are local
A geocentric phase instant is represented by one UTC timestamp in this approximation. Local clocks may show different dates even though no new phase event has occurred.
The configured night window is intentionally simple. True observing conditions require local moon altitude, rise/set times, twilight, weather, and horizon information.
Calculation method
Find one UTC phase instant before applying local clock labels
The next selected major phase is solved in UTC. Each fixed offset then produces a local timestamp, date-shift label, and night-window state.
Detailed calculation process and general formulas
T_phase = first(epoch + (k + φ/4)P_syn ≥ T_start)T_i = T_phase + z_ih_i = mod(hour(T_phase) + z_i, 24)Δd_i = date(T_i) − date(T_phase)night_i = [h_i ≥ 24 − H/2] ∪ [h_i ≤ H/2]Symbols, meanings, and units
- T_phase, φ
- modeled UTC event and selected phase indexdate-time; dimensionless
- z_i, T_i
- fixed offset and local event timestamp for location ihours; date-time
- h_i
- local clock hourhours after midnight
- Δd_i
- local-date shift relative to UTCdays
- H, night_i
- configured night-window width and membership statehours; boolean
Cross-zone interpretation
Date labels and nighttime opportunity can disagree
A location can share the UTC calendar date yet receive the event in daylight, while another crosses into the next date near local midnight.
UTC anchor
—Single modeled phase instant used by all locations.
Date spread
—Number of different civil dates represented.
Night-window count
—Locations inside the configured midnight-centered window.
Clock separation
—Largest wrapped local-clock difference.
Decision takeaway: Coordinate using UTC, publish local labels, and obtain site-specific visibility forecasts separately.
Location review
Site information required beyond a time-zone comparison
- Latitude and longitude
- Moon altitude and azimuth
- Moonrise and moonset
- Civil, nautical, or astronomical twilight
- Cloud, terrain, and access conditions
Comparison sources
Authoritative inputs for the final event plan
- Precision phase ephemeris
- IANA time-zone database
- Site coordinates
- Local twilight calculation
- Weather and horizon assessment
Practical applications
Decisions this calculator is designed to support
Three-continent observation coordination
Teams compare a full-moon instant across UTC−8, UTC, and UTC+10.
What the result clarifies: The orbit exposes distinct local dates and night-window states around one shared instant.
Date-publication check
An organizer needs local calendar labels for notices.
What the result clarifies: The table prevents publishing the UTC date as though it were universal.
Worked example
Current-input substitution and reconciliation
Model limitations
This calculator uses a mean-cycle phase estimate and fixed offsets. Its night window is only a clock-time proxy. It does not calculate DST automatically, local darkness, moon altitude, moonrise, weather, terrain, eclipses, tides, or observational safety.
Moon Phase Date Time-Zone Comparison Calculator FAQ
Does each location have a different full-moon instant?
No. The modeled event instant is shared; only local clock and date labels differ.
Why can the event show on two local dates?
Time-zone offsets place the same UTC instant on different sides of local midnight.
Does the night-window state mean the moon is visible?
No. It only tests local clock time around midnight.
How should daylight saving be handled?
Enter the correct fixed offset for each location on the event date or use an authoritative time-zone converter.