dusk

Dusk is the period between sunset and complete darkness. It is also referred to as twilight, evening, or nightfall. In atmospheric science, dusk is related to the scattering of sunlight by particles in the atmosphere. This scattering effect, known as Rayleigh scattering, causes shorter, bluer wavelengths of light to scatter more than longer, redder wavelengths.12

During sunrise and sunset, sunlight travels through more of the atmosphere. This increased path length causes most of the blue light to scatter away, leaving the longer wavelengths of red and orange light to reach our eyes, which is why the sky often appears red or orange at these times. Civil twilight is a specific phase of dusk, defined as the period when the sun is about 6 degrees below the horizon, and there is still enough light for outdoor activities.23