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What is the time of sunrise, if official day starts at 05:35?

  • A

    06:05

  • B

    05:35

  • C

    05:50

  • D

    05:20

In aviation, “Official Day” or “Daylight” typically begins at the start of the morning civil twilight. It occurs when the centre of the sun is 6° below the horizon, approximately 30 minutes before sunrise at mid-latitudes. 

The duration of twilight, and thus the start of “Official Day”, is highly dependent on both your latitude and the season. The 30-minute rule used is a standard "rule of thumb" for middle latitudes, but the actual time the sun takes to reach 6° below the horizon (the start of civil twilight) varies significantly.

To determine the time of sunrise, add 30 minutes to the start of the “Official Day” (morning civil twilight):

  • 05:35 + 30 minutes = 06:05

Regarding the other options:

  • 05:20 is 15 minutes before the start of the official day.
  • 05:35 is the start of the official day itself, not the sunrise.
  • 05:50 is 15 minutes after the start of the official day, and 15 minutes before the sunrise.

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