Final answer:
The definition of nighttime is the time between the end of evening civil twilight and the beginning of morning civil twilight.
Step-by-step explanation:
The definition of nighttime is: c) The time between the end of evening civil twilight and the beginning of morning civil twilight. Civil twilight is the period when the Sun is between 0° and 6° below the horizon. It is a common definition used to determine when it is dark enough to see stars but still have some residual light from the Sun. Nighttime is typically considered to be the period when most people sleep and is associated with darkness.