A Coruña Civil, Nautical & Astronomical Twilight · FastTool

Twilight Duration at A Coruña

At A Coruña's latitude of 43.4°, 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 A Coruña's dark-sky window so different month to month.

A Coruña sits directly on the centerline of the August 12, 2026 total solar eclipse — the longest totality (1 minute 58 seconds) of any major city in the path. The city's Tower of Hercules, a UNESCO World Heritage Roman lighthouse dating from the 1st century, has watched over this Atlantic coastline for nearly 2,000 years and will witness the Moon's shadow sweep across the Bay of Biscay.

When Does It Get Truly Dark in A Coruña?

At A Coruña, true astronomical darkness begins when the sun drops more than 18° below the horizon — the end of astronomical twilight. At 43.4° latitude, this dark window varies from approximately 4–6h in summer to 12–14h in winter. During the October–March months, A Coruña 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 43.4°N on Spain's northwestern Atlantic coast, A Coruña's sun path is shaped by the Cantabrian Sea: summer sunsets linger past 10 PM over the water, creating extended golden hours that attract photographers to its glass-fronted Paseo Marítimo — the longest seaside promenade in Europe at over 13 km.

Civil, Nautical & Astronomical Twilight Explained

Three twilight phases occur each evening and morning at A Coruña, 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 A Coruña'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 A Coruña 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 A Coruña's coordinates.