About LNBT

LNBT is Local Noon-Based Time: a public clock anyone can open in a browser. Your device finds the largest nearby metro area in our catalog whose solar noon stays within about 15 minutes of your location’s sun, and LNBT sets 12:00 to that place’s true solar noon (sun on the meridian, including the Equation of Time). Noon-close twins are merged into one named zone (e.g. Twin Cities / MSP, Metroplex / DFW, Capital / DMV) so alarms read like LNBT(MSP). The 15‑minute cap keeps remote places from snapping to a distant mega-metro that would warp noon by half an hour or more.

Show the map

Interactive CONUS coverage: which metro owns each land cell under the 15‑minute noon window (product vs unconstrained vs pure nearest).

Why

Civil time zones are political rectangles. Solar noon is physical. People who share a metro already share roughly the same sun. LNBT makes that shared day legible without installing an app.

Three roles of time

• LNBT (local sun) — when the day feels like noon at your reference city. Best for school, church, office hours, and anyone under the same metro sky.
• Civil / legal — what phones, banks, and governments use today (including daylight saving when a zone observes it).
• UTC — one shared instant for the whole planet. Use this (or a calendar invite) when people live far apart — different cities, coasts, or countries.

Same reference city → same LNBT digits. Far apart → set the meeting on a shared instant (UTC / calendar); each person’s LNBT is just their local sun view of that same moment. As city centers stabilize, scheduling tools can show both sides of that conversion automatically.

How the clock is calculated

Solar math is computed first-party (this site + open algorithms) — not scraped from a third-party solar website.

1. Pick a reference city. You choose a metro area, or we take your coordinates and select the largest catalog metro within expanding search radii (50 → 100 → 150 → 250 → 400 → 800 km) and within a ~15 minute solar-noon window of your longitude (4 minutes per degree east/west; north–south distance does not move noon). Small satellites within ~5–10 minutes of noon of a larger hub share that hub’s zone name and code. That is “largest nearby shared sky in our list,” not your exact GPS pin as the clock origin. If the seed catalog has no city inside the window, we fall back to the nearest listed city and show the noon gap (a denser catalog is the long-term fix). You can always override with the city picker.
2. Longitude → mean solar time. The Earth turns 360° in 24 hours, so each degree of longitude is 4 minutes (15° per hour). Mean solar noon at longitude L is about 12:00 UTC − L/15 hours.
3. Equation of Time (EoT). Earth’s orbit is not a perfect circle and its axis is tilted, so sundial noon drifts from mean noon by roughly ±16 minutes over the year. We add a compact EoT approximation (accurate to about a minute on most days): EoT ≈ 9.87·sin(2B) − 7.53·cos(B) − 1.5·sin(B) with day-angle B from the day of year.
4. True solar time = LNBT. LNBT hours = UTC hours + L/15 + EoT/60, wrapped into a 0–24h day. By construction, 12:00 LNBT is solar noon at the reference city’s longitude.
5. Civil comparison. Legal wall time at the city uses the standard IANA time zone for that lat/lon (with daylight saving when that zone observes it). The offset you see between LNBT and civil combines longitude vs the zone’s standard meridian, EoT, and any DST hour.

After the locality is saved, the clock ticks in your browser (EoT refreshes as the UTC day rolls). The server is for picking a city, share links, and a light midnight tally — not a continuous per-second stream.

Alarms (free)

The free clock offers up to three browser alarms: one-time (today or a future date) or recurring (daily / weekly). You may set each alarm in LNBT or civil time. Alarms fire only while this tab (or device) keeps the page alive enough for the browser to run the timer and show a notification — they are not a replacement for the phone’s system alarm app.

Propose a meeting (free)

Propose a meeting builds a share link for one appointment: set the time in civil or LNBT at your hub. The recipient picks their city and sees host LNBT, guest LNBT, civil times, and the shared UTC instant — then can download a calendar file (.ics), set a reserved 4th browser alarm (does not use free alarms 1–3), and Accept or Decline so the proposer sees a notice (status link on the server + optional email draft if they left an address). Guest can also send a notice link back. Calendar files (.ics) store the meeting as an absolute UTC instant; your calendar app should display that in your normal civil time (the file title/description also list LNBT and civil). Notify email is remembered in this browser for the next proposal. Open the free LNBT clock for their own metro. No accounts required. A fuller booking page with Google Calendar / Outlook is a later paid direction, not this free tier.

What we keep simple

• No accounts required for the clock
• Location used only in your browser session to pick a city — not logged as a profile
• Phones stay on normal legal time; LNBT is the shared sun clock you open when you need it
• Servers and precision systems should still use UTC
• Self-hosted (e.g. Synology + reverse proxy + HTTPS)

Host

Public site: lnbt.org. Ops notes live in the repo under docs/.