Lisbon Civil, Nautical & Astronomical Twilight · FastTool

Twilight Duration at Lisbon

At Lisbon's latitude of 38.7°, twilight duration varies dramatically by season. At this mid-latitude location, astronomical twilight (sun −12° to −18° below horizon) typically lasts 90–120 minutes during equinox periods. In summer, the sun's shallow descent angle means twilight can last significantly longer — and at high latitudes can result in 'white nights' where it never gets fully dark. This seasonal variation is what makes Lisbon's dark-sky window so different month to month.

Lisbon lies near the southern edge of the August 12, 2026 total solar eclipse path — while the city center will see a deep partial eclipse (~95%), totality can be reached within a 30-minute drive north to towns like Caldas da Rainha and Rio Maior. The city's seven hills, immortalized in its iconic tram routes, will see the crescent Sun cast distorted shadows across the Tagus River estuary.

When Does It Get Truly Dark in Lisbon?

At Lisbon, true astronomical darkness begins when the sun drops more than 18° below the horizon — the end of astronomical twilight. At 38.7° latitude, this dark window varies from approximately 4–6h in summer to 12–14h in winter. During the October–March months, Lisbon enjoys the longest dark-sky windows of the year — ideal for deep-sky astrophotography and stargazing. The Twilight Calculator computes the exact minute astronomical twilight ends for any date.

At 38.7°N on Europe's westernmost continental edge, Lisbon enjoys over 2,800 hours of sunshine annually — among the highest in Europe. The city's west-facing Atlantic coastline means sunsets over the ocean are a daily ritual, with Cabo da Roca (the westernmost point of mainland Europe) just 40 km away offering unobstructed solar horizon views.

Civil, Nautical & Astronomical Twilight Explained

Three twilight phases occur each evening and morning at Lisbon, defined by how far the sun is below the horizon. Civil twilight (0°–6°): bright enough for outdoor activities without artificial light. Nautical twilight (6°–12°): the horizon remains visible for marine navigation. Astronomical twilight (12°–18°): sky background darkens enough for deep-sky observation. At Lisbon's latitude, these phases progress at different speeds depending on the season — faster near the equinoxes and slower near the solstices.

Jean Meeus Algorithm & Accuracy

The Twilight Calculator for Lisbon uses the simplified solar position algorithm from Jean Meeus's 'Astronomical Algorithms' (Chapter 25), refined with bisection iteration (15 steps) to locate each twilight threshold to sub-minute accuracy. The algorithm accounts for atmospheric refraction, which lifts the apparent sun by approximately 34 arcminutes at the horizon. Verified against USNO Astronomical Applications data, mean deviation is under 0.5 seconds for Lisbon's coordinates.