Safe Use & Disclaimers

Not to be used for

You must not use thirdtrail data as a sole or primary source for, among other things:

• Aviation — flight planning under VFR or IFR; determining the legal start/end of night; pilot night-currency windows; or aircraft position/anti-collision and landing-light timing.
• Maritime — navigation, passage planning, the timing of navigation lights (“lights on/off”), or celestial navigation.
• Tides — under-keel or air-draft clearance, berthing or bar-crossing decisions, or any depth-critical operation. Our tide heights are astronomical model output (FES2022): they exclude weather-driven surge, seiches and river discharge, and they are not official tide tables. Actual water level can differ by a metre or more in storm conditions.
• Search and rescue, emergency response, or any other operation where the timing of daylight, darkness or twilight affects safety of life.
• Regulatory compliance of any kind that depends on an authoritative sunrise, sunset or twilight time.

Why our times differ from the official “legal” times

Aviation and maritime regulators define the day/night boundary using civil twilight at the standard, level horizon, as published by official almanac authorities — not corrected for the observer's elevation or local terrain. thirdtrail deliberately does the opposite: we apply a geometric horizon-dip correction for your elevation, so at altitude our sunrise is earlier and our sunset/dusk is later than the standard published time.

That makes our numbers excellent for the use cases we serve (photography, solar siting, observation at altitude), but it means they can portray a longer usable day than a regulator recognises. Relying on them to decide when you may legally fly or navigate could place you outside the permitted window. The relevant official definitions:

• FAA (United States) — “night” is the period between the end of evening civil twilight and the beginning of morning civil twilight, as published in the Air Almanac (14 CFR § 1.1); see also night currency (14 CFR § 61.57) and lighting, sunset to sunrise (14 CFR § 91.209).
• EASA / Europe — “night” is the hours between the end of evening civil twilight and the beginning of morning civil twilight, with civil twilight ending when the centre of the sun's disc is 6° below the horizon (Standardised European Rules of the Air, Reg. (EU) 923/2012 — SERA).
• ICAO — Annex 2 (Rules of the Air) is the international baseline from which the above national definitions derive.
• U.S. Naval Observatory — its rise/set tables explicitly assume “a level region on the Earth's surface,” i.e. they are not corrected for observer elevation or terrain (Rise, Set & Twilight definitions).

For exactly how we compute and our published accuracy per field, see our methodology.

Use these official sources instead

• Your national Aeronautical Information Service / AIP, and the official almanac your authority designates (e.g. the Air Almanac / USNO in the US).
• Your aviation regulator (FAA, EASA and the relevant national authority, etc.) for the binding definition of night, currency and lighting.
• Your maritime authority and official nautical almanac for navigation-light timing and celestial navigation.

Your responsibility

You are responsible for independently verifying any time-critical value against an authoritative source before acting on it, and for ensuring your use complies with all applicable law and regulation. This page supplements, and does not limit, our Terms and Conditions — including the “Acceptable use”, “Disclaimers”, “Limitation of liability” and “Indemnity” sections.

Contact

Questions about appropriate use: support (at) thirdtrail.life.