Data sources and calculation methods
By the Time Aligner project · Content revision:
Time zones and calendar exports
City times use the IANA time zone database through JavaScript Intl in the hosting and browser runtimes. Database updates depend on those runtimes. Governments can change rules at short notice, so check the relevant authority for a critical future appointment.
EST, CST, MST and PST denote fixed standard offsets. ET, CT, MT, PT and city selections follow seasonal rules. A date matters: an hour skipped by a spring clock change is rejected, and a repeated autumn hour offers first or second occurrence. Calendar exports resolve the selected occurrence to UTC under RFC 5545. “Export” means a download was initiated, not that a calendar application imported it.
Sun and Moon
Sunrise, sunset, moonrise, moonset, transit and lunar phase use Astronomy Engine 2.1.19 (MIT license). Calculations use the target city’s local civil day, including 23- and 25-hour days, and observer elevation zero. Rise and set use the engine’s upper-limb and atmospheric refraction model. Buildings, hills, observer height and actual weather can change what you see.
Civil, nautical and astronomical twilight use the Sun’s centre at −6°, −12° and −18°. Our golden-hour range is the centre between −6° and +6°; this is a photographic convention, not a fixed hour. Daylight is the total time above the model horizon within the selected civil day. A dash means no event within that day; at high latitudes this includes polar day or night. Times round to the nearest minute; (+1) explicitly marks rounding into the next local date.
The date controls support 1900–2100. Regression samples cover eight locations and 2026 equinox, solstice, DST and polar cases against MET Norway Sunrise 3.0. The acceptance tolerances are three minutes for solar and five minutes for lunar events. These are test tolerances for those samples, not a worldwide accuracy guarantee. MET’s solar-day responses can include an event on a neighbouring civil date; we compare the same local event.
Weather
Forecast data is from MET Norway Locationforecast 2.0, licensed under CC BY 4.0. Time Aligner transforms the forecast samples into local-day summaries and converts wind speed from metres per second to kilometres per hour. MET Norway does not endorse this site.
Temperature high/low and maximum wind are extrema of the available samples, not full-day observations or guaranteed daily extrema. Rain sums only non-overlapping intervals wholly inside the local date; the number of covered hours is shown. The forecast horizon varies, up to ten calendar dates, and edge days can be partial.
The server identifies itself to the provider, stores forecasts in Cloudflare R2, honours the provider’s expiry and uses conditional requests. Requests refresh at most hourly with a small delay; failures retry after five minutes. The source’s update time is visible. Forecasts older than six hours are marked stale; data older than 24 hours is hidden. When no usable cache exists the page shows an unavailable state instead of invented values.
Holidays
Where available, holiday lists use Nager.Date API snapshots. Source links and retrieval dates appear on each page. The stored range is 2025–2028; refreshing data is an explicit maintenance operation. The current snapshots were retrieved on 23 October 2026. Data is a planning aid, not an official declaration.
Nationwide and regional labels preserve the provider’s global flag and ISO subdivision codes. Public, bank, school, optional and observance types remain distinct. Duplicate entries merge only when their date, names and geographical scope agree. Display years follow the actual supplied calendar date, including substitute days crossing New Year. The provider does not separately identify every nominal versus substitute day; confirm local law, employer rules and official announcements.
India retains a clearly marked unverified legacy list and is excluded from the sitemap. A missing year shows no verified data; it never borrows a different year’s dates. Stored snapshots older than 180 days are flagged, and maintenance checks require the current and next year.
Usage and performance
Optional analytics count successful explicit conversions, successful result copies and calendar-download initiation on the converter. Failed or empty results do not count. Event payloads contain tool type and locale, not entered times, copied contents or meeting details. With analytics consent, LCP, INP and CLS can be collected for performance review. Search impressions and clicks come separately from Google Search Console; they are not tool-completion counts.
Maintenance history
23 October 2026: documented sources, replaced the simplified astronomy algorithms, added weather caching and refreshed holiday snapshots. See the public change history for released revisions. Report corrections through Contact.