Taipei Civil, Nautical & Astronomical Twilight · FastTool

Twilight Duration at Taipei

At Taipei's latitude of 25.0°, 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 Taipei's dark-sky window so different month to month.

Taipei sits near the Tropic of Cancer at 25°N — the latitude where the Sun reaches exactly 90° altitude at the June solstice, casting no shadow at solar noon. The city's National Museum of Natural Science operates a dedicated solar observatory that tracks the Sun's zenith passage, and the Tropic of Cancer landmark in Chiayi draws thousands of visitors each June to witness the 'no shadow day' phenomenon.

When Does It Get Truly Dark in Taipei?

At Taipei, true astronomical darkness begins when the sun drops more than 18° below the horizon — the end of astronomical twilight. At 25.0° latitude, this dark window varies from approximately 4–6h in summer to 12–14h in winter. During the October–March months, Taipei 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.

Taipei at 25°N experiences a relatively modest 3.5-hour seasonal daylight swing between summer and winter — the smallest among East Asian capitals. This equatorial proximity means the city's golden hours are more consistent year-round than at higher latitudes, with the Sun rising and setting at steeper angles that create crisp, dramatic shadows in Taipei's narrow alleyway culture.

Civil, Nautical & Astronomical Twilight Explained

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