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Which statement is true?
  • A
    Only the declination of the Sun will affect the duration of civil twilight.
  • B
    The declination of the Sun and the latitude of the observer will affect the duration of civil twilight.
  • C
    The duration of the civil twilight on 21st of March and on 23rd of September is equal at all places on Earth independent of latitude.
  • D
    Civil twilight at the Equator lasts longer than at 60°N or 60°S because the radius of the Equator is larger than the radius of the 60° parallel.

CIVIL TWILIGHT

Each twilight phase is defined by the solar elevation angle, which is the position of the Sun in relation to the horizon. During civil twilight, the geometric center of the Sun's disk is at most 6 degrees below the horizon.

The duration of each twilight phase depends on:

  • The latitude - At higher latitudes, in both hemispheres, the Sun's path makes a lower angle with the horizon, so the twilight phases last longer.

  • The declination of the sun (and, consequently, the time of the year) - when the sun's position coincides with the observer's hemisphere, the twilight phases last longer (declination increases).

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