Twilight Type

ATRONOMY – COORDINATE YTEM & TIME (30) CALCULATOR Twilight Type A precise tool.
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What is the Twilight Type & How does it work?
Twilight is the period between day and night when the Sun is below the horizon but its light is still scattered in the atmosphere. Depending on how far the Sun lies beneath the horizon, astronomers distinguish three main categories: civil twilight (Sun 0° to –6°), nautical twilight (Sun –6° to –12°) and astronomical twilight (Sun –12° to –18°). These intervals are important for navigation, photography, and observational astronomy. The Sun’s depression angle, often denoted by (theta), can be calculated from the observer’s latitude ((phi)), the Sun’s declination ((delta)) and the hour angle ((h)). The relationship is given by the spherical‑trigonometric formula below, which derives from the cosine rule for the celestial sphere.
\theta = \arccosbigl(-\sin(\phi) \sin(\delta) – \cos(\phi) \cos(\delta) \cos(h)bigr)
theta = Sun’s depression angle below the horizon (degrees)
Once (theta) is known, the twilight type is determined by simple thresholds: if (theta) is between 0° and –6° the sky is in civil twilight, between –6° and –12° it is nautical twilight, and between –12° and –18° it is astronomical twilight. Outside these ranges the Sun is either fully above the horizon (day) or far enough below (night).
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Frequently Asked Questions
What is civil twilight?
Civil twilight occurs when the Sun is between 0° and –6° below the horizon.
How do I determine nautical twilight?
Nautical twilight happens when the Sun is between –6° and –12° below the horizon.
What is astronomical twilight defined as?
Astronomical twilight occurs when the Sun is between –12° and –18° below the horizon.
Why are twilight periods important for astronomy?
Twilight periods are crucial for observational astronomy as they help in planning observations and avoiding bright sky conditions.
How can I use this calculator to plan my photography sessions?
Enter the Sun’s depression angle into the calculator to determine twilight periods, which are ideal for low-light photography without a flash.

Results are for informational purposes only and do not constitute professional advice.