soumrak

Soumrak is a term used in Czech and Slovak to describe the period after sunset when the sky remains illuminated by sunlight scattered in the atmosphere, before darkness fully sets in. It results from the sun being below the horizon and depends on atmospheric scattering, the observer’s latitude, and the season.

The concept encompasses three subtypes defined by the sun’s angle below the horizon. Civilní soumrak (civil twilight) occurs when the sun is between 0 and 6 degrees below the horizon and provides enough light for most outdoor activities without artificial illumination. Námorní soumrak (nautical twilight) lasts from about 6 to 12 degrees below the horizon, when the horizon at sea becomes just distinguishable. Astronomický soumrak (astronomical twilight) extends from about 12 to 18 degrees below the horizon, after which the sky is typically dark enough for most astronomical observations.

Geographically and seasonally, soumrak varies significantly. At mid-latitudes it lasts tens of minutes to over an hour, depending on the season. Near the poles, twilight can be very long in spring and autumn, while in summer there may be only a brief dusk or none at all during midnight sun periods. In winter, twilight is shorter in higher latitudes and can be relatively dim even during civil twilight. Urban light pollution often diminishes the perceived brightness and color of soumrak.

In everyday language, soumrak also carries metaphorical and poetic connotations and appears in literature and media to evoke transition, fading light, or the approach of night. The term is an integral part of the meteorological and astronomical vocabulary in Czech and Slovak.