Twilight Duration Calculator

Civil twilight occurs when the sun is between 0° and 6° below the horizon. During this phase, there is still enough natural light to carry out most outdoor activities without artificial lighting. It begins at civil dawn (morning) and ends at civil dusk (evening).

Nautical twilight occurs when the sun is between 6° and 12° below the horizon. Historically, sailors could use this period to navigate by the stars while still seeing the horizon. The sky is noticeably darker than during civil twilight, and only bright stars are visible.

Astronomical twilight occurs when the sun is between 12° and 18° below the horizon. During this phase, the sky becomes dark enough for most astronomical observations, though faint celestial objects near the horizon may still be affected by residual scattered light.

Twilight duration depends on the angle at which the sun descends below the horizon, which changes with latitude and time of year. At higher latitudes, the sun sets at a shallower angle, making twilight last longer. Near the equator, the sun sets more steeply, so twilight is shorter. During summer solstice at high latitudes, twilight can last all night.

This calculator uses standard solar position algorithms (based on Jean Meeus's Astronomical Algorithms) to compute sunrise, sunset, and twilight times accurate to within 1–2 minutes for most locations and dates between 1700 and 2100. Results may deviate slightly for extreme latitudes or dates far from the present.

Enter your local standard time offset from UTC in hours. For example, Eastern Standard Time (EST) is UTC−5, so enter −5. Central European Time (CET) is UTC+1, so enter 1. If your region observes daylight saving time, add 1 hour during that period (e.g. EDT = −4). Half-hour zones like India Standard Time (IST) would be +5.5.

Yes — at high latitudes during summer, the sun may never descend below 18° below the horizon, meaning astronomical twilight persists throughout the night. This phenomenon is related to the 'white nights' experienced in cities like St. Petersburg or Reykjavik. At very high latitudes, even civil twilight can last the entire night around the summer solstice.

Dawn refers to the morning phase when the sky begins to brighten before sunrise, while dusk refers to the evening phase after sunset when the sky darkens. Each type of twilight (civil, nautical, astronomical) has both a dawn and a dusk period, producing six twilight transition points per day.