Twilight (civil, nautical, astronomical)
Twilight is the period before sunrise and after sunset when the sky is partly lit by the Sun below the horizon, split into civil, nautical and astronomical stages.
Civil twilight lasts until the Sun is 6° below the horizon, nautical to 12° and astronomical to 18°, after which the sky is fully dark.
Satellites are easiest to spot during twilight, when they still catch sunlight against a darkening sky, while the deep dark after astronomical dusk is best for faint objects.
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Related terms
- Azimuth — Azimuth is the compass direction to an object in the sky, measured in degrees clockwise from true north — 0° is north, 90° east, 180° south, 270° west.
- Kp index — The Kp index is a 0–9 scale of global geomagnetic activity over three-hour periods, and it is the number aurora watchers check to judge tonight's odds.
