ケープタウンの薄明時刻 — Twilight Calculator · FastTool

Twilight Duration at ケープタウン

At ケープタウン's latitude of -33.9°, 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 ケープタウン's dark-sky window so different month to month.

ケープタウンには、天文台（Observatory）地区に南アフリカ天文台（SAAO）があります——南半球最古の常設天文台で、1820年から運用されています。市街地の背後にそびえる標高1,085mのテーブルマウンテンは、「テーブルクロス」と呼ばれる独特の地形性雲現象を生み出します——南東風が湿った空気を山肌に押し上げることで形成される雲の層で、市街地のボウル全体に劇的な日没のシルエットを映し出します。

When Does It Get Truly Dark in ケープタウン?

At ケープタウン, true astronomical darkness begins when the sun drops more than 18° below the horizon — the end of astronomical twilight. At -33.9° latitude, this dark window varies from approximately 4–6h in summer to 12–14h in winter. During the October–March months, ケープタウン 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.

南緯33.9度のケープタウンは、12月の夏至に14時間25分の日照で祝います——アフリカ最南端の真夏です。二つの大洋（大西洋とインド洋）に挟まれた半島に位置するこの街では、太陽がインド洋から昇り、大西洋に沈みます——世界中の沿岸都市でもほんの一握りしか持たない稀有な地理的特権です。

Civil, Nautical & Astronomical Twilight Explained

Three twilight phases occur each evening and morning at ケープタウン, 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 ケープタウン'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 ケープタウン 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 ケープタウン's coordinates.