Regulations Reference
Use the Civil Twilight Calculator below to find sunrise, sunset, and civil, nautical, and astronomical twilight times for any location and date. The calculator displays FAA night currency windows, UK night definition periods, and position light requirements.
Usage Guide
Follow the steps below to use the Civil Twilight Calculator to find sunrise, sunset, and twilight times for any location and date.
Enter the latitude and longitude of your aerodrome or intended flight area. Positive latitude = North, negative = South. Positive longitude = East, negative = West. Use the quick location buttons for common cities, or find coordinates for your aerodrome from the AIP, Jeppesen charts, or a GPS device. ICAO aerodrome coordinates are listed in their AIP entry.
Select the date of your planned flight. Civil twilight times change significantly through the year — particularly at higher latitudes. For pre-flight planning, check the date of the actual flight. For annual planning, check summer and winter solstices to understand the extremes of your operating environment.
Enter your local time zone offset from UTC — for example, UTC+1 for UK BST, UTC-5 for US Eastern Standard Time, or UTC+10 for AEST. All calculated times are shown in both UTC and local time. Always brief and file in UTC; use local time for scheduling and passenger information only.
Once all inputs are entered, the results panel displays a 24-hour solar timeline showing daylight, civil twilight, nautical twilight, astronomical twilight, and night in colour. Below the timeline, the morning and evening columns list the exact times for astronomical dawn, nautical dawn, civil dawn, sunrise, sunset, civil dusk, nautical dusk, and astronomical dusk — shown in both UTC and local time.
The regulatory periods panel shows the exact windows for: the FAA position light requirement (sunset to sunrise), the FAA night currency period (end of evening civil twilight to beginning of morning civil twilight), the one-hour-before and one-hour-after sunset window for logging night flight time, and the UK night definition. Use these times for pre-flight briefings and currency self-assessment.
Definition
Civil twilight is the period when the Sun is between 0° and 6° below the horizon, providing enough natural light for most outdoor activities without artificial illumination.
Civil twilight occurs twice each day. Morning civil twilight begins when the Sun reaches 6° below the horizon and ends at sunrise. Evening civil twilight begins at sunset and ends when the Sun reaches 6° below the horizon. During this period, the sky remains bright because sunlight is scattered through the Earth's atmosphere even though the Sun is below the horizon.
Civil twilight is one of the three recognized twilight phases. It occurs before nautical twilight and astronomical twilight in the morning, and after them in the evening. Among the three phases, civil twilight provides the greatest amount of natural light.
In aviation, civil twilight is important because many regulations define day and night operations using the beginning or end of civil twilight. Pilots use published civil twilight times to determine when specific lighting, equipment, and flight rules become applicable under national aviation regulations.
Civil twilight times vary with date, latitude, and longitude because the Sun's apparent path across the sky changes throughout the year and across different locations on Earth. A civil twilight calculator determines these times by calculating when the Sun's geometric center reaches 6° below the horizon for a specific location and date.
Twilight vs Sunset
Civil twilight is a period of reduced natural daylight, while sunset is the exact moment when the Sun's upper edge disappears below the horizon.
Sunset marks the beginning of evening civil twilight. After sunset, the Sun continues to illuminate the atmosphere from below the horizon, so the sky remains bright enough for most outdoor activities without artificial lighting. Evening civil twilight ends when the Sun reaches 6° below the horizon, after which nautical twilight begins.
In the morning, the sequence is reversed. Morning civil twilight begins when the Sun reaches 6° below the horizon and ends at sunrise, which is the moment the Sun's upper edge first becomes visible above the horizon.
The duration between sunset and the end of evening civil twilight varies throughout the year and changes with latitude. Near the equator, civil twilight is relatively short, while at higher latitudes it lasts much longer because the Sun follows a shallower path below the horizon.
In aviation, sunset and civil twilight are different operational reference points. Many aviation regulations define the start or end of certain day and night operations using civil twilight, not sunset alone. Pilots therefore use published civil twilight times rather than sunset times when determining regulatory compliance.
Solar Calculation
Civil twilight is calculated by determining the times when the Sun's geometric center is exactly 6° below the horizon for a specific date and location.
The calculation uses the observer's latitude, longitude, date, and time zone together with the Sun's predicted position in the sky. Astronomical algorithms determine the Sun's elevation angle throughout the day and identify the two moments when it reaches −6°. The morning event marks the start of civil twilight, and the evening event marks the end of civil twilight.
The Sun's elevation angle is commonly calculated using the following astronomical relationship:
sin(h) = (sin(φ) × sin(δ)) + (cos(φ) × cos(δ) × cos(H))
Where:
Astronomical software solves this equation for the hour angle when h = −6°. The resulting hour angle is then converted into the local civil twilight time using the observer's longitude, date, and time zone.
Civil twilight calculations account for the Earth's rotation, its orbit around the Sun, and the tilt of its rotational axis. These factors change the Sun's apparent path across the sky throughout the year, causing civil twilight times to vary by season and location.
Most civil twilight calculators use standardized solar position models published by the National Oceanic and Atmospheric Administration (NOAA) or based on astronomical reference models adopted by the International Astronomical Union (IAU). These models produce highly accurate civil twilight times for almost any location on Earth.
A civil twilight calculator does not measure weather conditions or sky brightness. It calculates twilight solely from the Sun's geometric position relative to the horizon. Cloud cover, haze, and local terrain may make the sky appear brighter or darker than the calculated twilight period, but they do not change the official civil twilight times.
Aviation Relevance
Civil twilight matters for pilots because many aviation regulations use it to determine when day and night operating requirements begin or end.
Civil twilight serves as a legal reference for several operational rules, including aircraft lighting requirements, pilot currency, and the definition of day and night in many jurisdictions. Pilots use published civil twilight times during flight planning to ensure compliance with the applicable regulations.
During morning civil twilight, natural light gradually increases before sunrise, improving visual references for terrain, obstacles, and other aircraft. During evening civil twilight, natural light gradually decreases after sunset, reducing outside visual cues as darkness approaches. These changing light conditions affect visual navigation and the pilot's ability to detect hazards.
Many aviation authorities, including the Federal Aviation Administration (FAA), European Union Aviation Safety Agency (EASA), and International Civil Aviation Organization (ICAO), publish regulations that reference civil twilight for specific operational purposes. The exact legal requirements vary by country, so pilots should always consult the regulations that apply to their flight.
Civil twilight is also important for flight planning because it helps pilots determine when to activate aircraft lighting, anticipate changing visibility, and prepare for the transition between daytime and nighttime operations. Using accurate civil twilight times reduces the risk of regulatory non-compliance and improves situational awareness before departure and during arrival.
VFR Operations
Civil twilight defines a key legal transition period in aviation, and VFR flight rules use it to determine when day VFR ends and night VFR requirements begin under regulatory frameworks such as the Federal Aviation Administration (FAA) system.
Civil twilight occurs when the Sun is between 0° and 6° below the horizon. VFR regulations use this period as the boundary between day operations and night operations for many legal requirements.
The FAA uses civil twilight to define when night passenger currency begins and ends under 14 CFR 61.57(b). Day VFR privileges end at the end of evening civil twilight, and night VFR operational requirements begin immediately after.
VFR flight remains fully legal during civil twilight if the pilot complies with the applicable airspace VFR minimums under 14 CFR 91.155. The aircraft can operate visually if visibility and cloud clearance meet the required limits for the airspace class.
Civil twilight is not a restriction on VFR flight by itself. It is a time reference for lighting, currency, and logging rules, not a visibility restriction.
Aircraft navigation lights must already be active at sunset under 14 CFR 91.209, and they remain required throughout civil twilight and into night operations.
During civil twilight, natural illumination decreases gradually. Terrain contrast reduces, horizon definition weakens, and pilot visual acquisition of traffic becomes more difficult compared to full daylight VMC.
Civil twilight affects VFR operations because it defines when pilots must transition from day visual operations to night visual operations.
VFR pilots use civil twilight times to plan:
Civil twilight therefore serves as a regulatory and operational boundary period, not a weather minimum.
Position Lights
Civil twilight determines when aircraft position lights must be used under regulations such as the Federal Aviation Administration (FAA) rules in 14 CFR 91.209, which define mandatory lighting periods for safe aircraft visibility.
FAA regulations require aircraft position lights (navigation lights) to operate from sunset to sunrise. This rule applies regardless of weather or visibility conditions.
Position lights include:
These lights help other aircraft determine direction of travel and aircraft orientation.
Civil twilight is not the legal trigger for position lights. The lighting requirement starts earlier, at sunset, and continues through civil twilight into full night.
Pilots must turn on position lights at sunset even if daylight conditions still appear strong on the ground.
Civil twilight reduces ambient light but does not remove visual meteorological conditions (VMC) by itself.
During civil twilight:
Position lights therefore become more important during this phase because they improve aircraft conspicuity in fading light conditions.
Pilots must treat sunset as the lighting activation point, not civil twilight.
Civil twilight is used for:
Position lights remain mandatory throughout civil twilight and continue into full night until sunrise.
Night Logging & Currency
Civil twilight determines the official boundary between day and night for FAA night currency requirements under Federal Aviation Administration regulations, especially 14 CFR 61.57(b), which governs passenger-carrying night proficiency.
FAA night currency requires pilots to complete takeoffs and landings between the end of evening civil twilight and the beginning of morning civil twilight.
This means:
Civil twilight provides a consistent astronomical reference based on the Sun's position at 6° below the horizon.
FAA night flight logging under 14 CFR 61.51(b)(3)(i) uses a broader definition of night:
This definition does not depend on civil twilight. It uses a fixed time buffer to include low-light conditions before full darkness.
Civil twilight creates a stricter operational boundary than logging rules because it aligns night operations with true loss of usable daylight illumination.
Pilots use civil twilight to:
Civil twilight is used for legal night currency, while sunset-based timing is used for flight logging.
This difference means a pilot may log night time before night currency requirements begin, but cannot carry passengers at night until civil twilight has ended.
UK Regulations
The United Kingdom defines night using civil twilight in aviation regulations published by the Civil Aviation Authority (CAA), with night beginning at the end of evening civil twilight and ending at the start of morning civil twilight.
UK aviation law uses civil twilight to define the official night period for flight operations and pilot licensing requirements.
Night begins when the Sun reaches 6° below the horizon after sunset and ends when the Sun reaches 6° below the horizon before sunrise.
This definition provides a consistent reference for all VFR and IFR operational rules in UK airspace.
Civil twilight determines when night privileges apply for pilots operating under UK licensing rules.
A pilot uses civil twilight to:
Without correct civil twilight timing, a pilot may log or operate night flight incorrectly under licensing rules.
UK night rating training and privileges use civil twilight as the operational boundary.
The night rating requires flight experience during the civil twilight-based night period, including dual instruction and solo operations under night conditions.
Civil twilight ensures that all training occurs under standardised low-light conditions consistent with ICAO definitions.
UK aviation uses civil twilight as the single reference for night operations, unlike FAA rules which use multiple definitions.
Pilots must always check civil twilight times in the UK Aeronautical Information Publication (AIP) or approved planning tools to determine legal night boundaries.
High Latitudes
High-latitude regions experience midnight sun, polar night, and extended twilight conditions because the Sun’s path remains shallow relative to the horizon, which alters civil, nautical, and astronomical twilight behaviour.
Midnight sun occurs when the Sun remains above the horizon for 24 hours during summer in polar regions.
The Sun stays continuously visible because the Earth’s axial tilt keeps polar regions pointed toward the Sun during summer months. Civil twilight does not occur in a normal daily cycle because sunset does not happen.
Polar night occurs when the Sun remains below the horizon for 24 hours during winter in polar regions.
The Sun stays continuously below the horizon because the Earth’s axial tilt points the region away from the Sun. Civil twilight may still occur depending on latitude, but full daylight does not return for extended periods.
The twilight paradox occurs when civil, nautical, and astronomical twilight overlap or repeat without a clear day–night transition.
At high latitudes:
This creates long periods where the Sun remains just below the horizon, producing extended twilight instead of distinct night or day.
High-latitude twilight conditions affect aviation operations because standard night definitions become less distinct.
Pilots and operators must rely on:
These conditions require careful planning because visual cues for horizon, lighting, and terrain can remain ambiguous for long periods.
Global Reference
Civil twilight duration varies by region because the Sun sets at different angles and speeds depending on latitude, which directly affects how long the Sun remains within 0° to 6° below the horizon.
Equatorial regions experience civil twilight durations of approximately 20 to 25 minutes per phase.
The Sun crosses the horizon at a steep angle, which causes rapid changes in illumination. Countries near the equator, such as Singapore and Kenya, experience consistent twilight timing throughout the year with minimal seasonal variation.
Mid-latitude regions experience civil twilight durations of approximately 30 to 50 minutes, with seasonal variation.
In regions such as the United States, Europe, and Japan, the Sun sets at varying angles across seasons. Summer produces longer civil twilight, while winter produces shorter civil twilight.
The Federal Aviation Administration (FAA) uses these region-dependent civil twilight times for defining night currency and operational rules.
High-latitude regions experience civil twilight durations that can exceed 60 minutes or more.
In countries such as Norway, Canada, and Iceland, the Sun remains close to the horizon for extended periods due to the shallow solar angle. Civil twilight can extend into long low-light periods, especially during summer months.
Polar regions experience extreme civil twilight behaviour due to the midnight sun and polar night cycle.
At latitudes above the Arctic and Antarctic Circles:
Civil twilight timing directly affects night definitions, VFR operations, and pilot currency requirements across all regions.
Pilots use civil twilight tables from official aviation sources such as the International Civil Aviation Organization (ICAO) to determine:
Civil twilight therefore functions as a global but location-dependent aviation reference standard.
Common Mistakes
Pilots commonly misinterpret civil twilight definitions, which leads to errors in night currency, flight planning, and legal compliance under rules published by the Federal Aviation Administration (FAA) and equivalent international aviation authorities.
Pilots often assume night begins at sunset, but civil twilight ends later when the Sun reaches 6° below the horizon.
This mistake leads to incorrect night currency timing because FAA 14 CFR 61.57(b) defines night currency using civil twilight, not sunset.
Pilots often apply a single “night” definition to all regulations.
Different rules use different definitions:
Mixing these definitions causes regulatory errors in flight planning and logbook entries.
Pilots often assume civil twilight duration is constant worldwide.
In reality:
Ignoring this variation leads to incorrect night planning in regions such as Canada, Scandinavia, and Alaska.
Pilots often use non-aviation apps that report sunset but not civil twilight.
Accurate civil twilight data requires aviation sources such as:
Incorrect data sources can cause legal night timing errors.
Pilots often assume civil twilight automatically restricts VFR flight.
Civil twilight does not restrict VFR flight by itself. VFR legality depends on airspace-specific VFR minimums under 14 CFR 91.155, not twilight timing alone.
Civil twilight only defines regulatory timing boundaries for lighting, logging, and night currency rules.
Common Questions
Civil, nautical, and astronomical twilight differ by the Sun's depression angle below the horizon and define three stages of natural light reduction. Civil twilight occurs at 0° to 6° below the horizon and provides strong ambient light with a clearly visible horizon. Nautical twilight occurs at 6° to 12° below the horizon and allows faint horizon visibility with bright stars visible. Astronomical twilight occurs at 12° to 18° below the horizon and produces near-dark conditions with negligible solar illumination.
Civil twilight is the most operationally important phase in aviation because regulatory rules use it to define night boundaries.
A night rating is not required to fly during civil twilight in FAA or UK/EASA systems because civil twilight is treated as a transition period, not night. In the Federal Aviation Administration (FAA) system, night privileges apply after civil twilight ends under 14 CFR 61.57(b). In UK and EASA systems, night operations begin after civil twilight ends and require a valid Night Rating for pilot-in-command privileges.
Civil twilight itself remains part of daytime VFR operations for regulatory purposes.
Pilots find civil twilight times using aviation almanacs, approved flight planning tools, or authoritative astronomical data sources. The FAA uses data derived from the US Naval Observatory Air Almanac for official civil twilight calculations. The UK CAA uses UK AIP and almanac-based data for operational planning.
Aviation-grade tools calculate civil twilight using the Sun's geometric position at 6° below the horizon. Consumer weather apps often report sunset only and do not provide civil twilight end times, which makes them unreliable for regulatory compliance.
The 30-minute window before sunrise and after sunset is a planning convention and not a formal FAA regulatory definition of night. Some operators use this period as a conservative buffer to anticipate low-light conditions during flight planning.
FAA regulations define night differently depending on context, including civil twilight for currency and specific time buffers for logging under 14 CFR 61.51(b)(3)(i). Pilots must not confuse this heuristic buffer with legal night definitions.
The Air Almanac is an official astronomical publication that provides standardised sunrise, sunset, and civil twilight data for aviation use. The United States Naval Observatory and HM Nautical Almanac Office produce the Air Almanac for global aviation reference.
Aviation authorities reference it because it provides consistent and location-specific civil twilight calculations for regulatory compliance, flight planning, and crew scheduling. Operators use it to determine exact night transition times across different latitudes and seasons.
Civil twilight duration increases near the summer solstice and decreases near the winter solstice due to changes in solar declination and daylight geometry. Mid-latitude locations experience longer twilight periods in summer, often extending 40–60 minutes.
High-latitude regions can experience extended or continuous twilight during summer due to shallow solar angles. In winter, civil twilight shortens significantly and night begins earlier. Pilots use seasonal twilight variation to adjust night operations, crew scheduling, and VFR-to-IFR planning.
Civil twilight is not the same everywhere because it depends on latitude, longitude, and date-specific solar geometry. Latitude controls the Sun's angle below the horizon and therefore controls twilight duration. Longitude controls local clock time for sunrise and sunset events.
Two airports at the same latitude experience similar twilight duration but different local timing. Pilots must use location-specific civil twilight data for operational accuracy.
Civil twilight does not directly affect FAA instrument currency requirements under 14 CFR 61.57(c), which apply independently of daylight conditions. Instrument currency requires specific procedures such as approaches, holds, and tracking tasks within a defined time period.
Civil twilight only affects when night operations begin for separate night-related currency rules. Instrument flight currency remains valid regardless of twilight state.
Civil twilight calculations are highly accurate, typically within 1–2 minutes when based on standard astronomical models such as those used by the United States Naval Observatory. These calculations assume a standard horizon at sea level without terrain obstruction.
Real-world terrain such as mountains or valleys can cause earlier visual sunset and shift perceived twilight conditions. Pilots operating in complex terrain must adjust planning using official aviation data rather than visual estimates.
Civil twilight calculations define legal daylight and night boundaries for drone operations under many national aviation authorities. The Federal Aviation Administration (FAA) uses civil twilight under 14 CFR Part 107 to define when night UAS rules apply.
Standard drone operations are permitted during civil twilight if anti-collision lighting requirements are met. Night operations after civil twilight require additional authorisation or compliance with night operation rules. Other ICAO-aligned authorities apply similar civil twilight definitions for UAS regulation.