öövalgustuse

Öövalgustuse, also known as twilight, is the period of time during which the sky is still illuminated after sunset or before sunrise, but the sun is below the horizon. This phenomenon occurs due to the scattering of sunlight by the Earth's atmosphere, which causes the sky to remain lit even when the sun is no longer directly visible.

Twilight is divided into three phases: civil twilight, nautical twilight, and astronomical twilight. Civil twilight begins when the sun is 6 degrees below the horizon and ends when it is 0 degrees below the horizon, marking the end of dusk and the beginning of night. Nautical twilight occurs when the sun is between 6 and 12 degrees below the horizon, and astronomical twilight happens when the sun is between 12 and 18 degrees below the horizon. The latter phase is the darkest and is often referred to as night.

Öövalgustuse is an important consideration for various activities, including navigation, photography, and astronomy. During twilight, the sky's color can range from a bright orange or red to a deep blue, depending on the angle of the sun and the amount of atmospheric particles present. The duration of twilight varies with the time of year and the observer's latitude, with longer twilight periods occurring closer to the poles and during the equinoxes.