Author: Mary Knapp

As we move away from Summer, we start losing daylight. At this time of the year, it is about 2 minutes of less sunshine per day. Usually weather reports feature sunrise and sunset times, but sometimes other terms are used. Twilight refers to the time before sunrise and after sunset when natural light is reflected by the upper atmosphere. “Civil twilight” is defined as when the sun is 6 degrees below the horizon. The horizon is still distinct, but it is the limit at which, with good weather conditions, objects can readily be distinguished. The brightest stars can usually be seen. “Nautical twilight” occurs when the sun is 12 degrees below the horizon. General shapes might be seen, but the horizon is indistinct and other lighting is usually needed for outdoor activities.

Civil Twilight (Public Domain)

Mary Knapp, Weather Data Library