The length of twilight varies significantly depending on latitude and time of year.

• At mid-latitudes like Greenwich, England (51.5°N), civil twilight lasts from about 33 to 48 minutes depending on the season

• Near the equator, civil twilight can be as short as 24 minutes because the Sun moves nearly perpendicular to the horizon

• At high latitudes near the poles, twilight can last for hours or even weeks. For example, within the polar circles, civil twilight can extend through the entire night during certain times of the year, resulting in "white nights" where it never gets completely dark

• At extreme latitudes above about 81°25' N or S, twilight can last for 24 hours continuously around the equinoxes

In general, twilight is the period before sunrise and after sunset when the Sun is below the horizon but still illuminates the sky indirectly

. The total duration of twilight (evening plus morning) is roughly twice the length of the evening or morning twilight alone

. To summarize:

• Near the equator: about 24 minutes per twilight (morning or evening)
• Mid-latitudes: 30–50 minutes per twilight
• Near poles: twilight can last several hours to weeks, or even 24 hours continuously

This variation is due to the angle at which the Sun moves relative to the horizon, which changes with latitude and season