diurnos

Diurnos is the plural form of diurno, used to describe anything related to daytime or activity that occurs during daylight hours. The term appears across disciplines such as biology, botany, astronomy and everyday language. Etymology: it comes from Latin diurnus meaning “of the day,” itself from dies, “day.” In biology, diurnal refers to organisms whose main activity period is during daylight, in contrast to nocturnal species that are active at night and crepuscular ones that are active during twilight. Some species are cathemeral, meaning they show irregular activity across day and night depending on conditions. Diurnal behavior is often linked to ecological factors such as predator avoidance, temperature and food availability.

In animals, diurnal species include many birds, primates, ungulates and humans; their sensory systems and physiology are adapted to daytime activity. In botany, many plants exhibit diurnal rhythms, with some flowers opening during the day to attract diurnal pollinators, while others close at night. In ecology, diurnal patterns influence the timing of pollination, foraging and interactions with other species.

In astronomy and Earth sciences, the term diurnal describes phenomena tied to the planet’s rotation. Diurnal motion refers to the apparent daily movement of stars and the Sun across the sky due to Earth’s rotation. The diurnal cycle, or 24-hour cycle, governs day–night changes and related processes, including temperature fluctuations and circadian rhythms in organisms.

In everyday language, diurnos may describe daytime activities or schedules, for example “horas diurnas” or “actividad diurna.” The term contrasts with nocturnos and is part of a broader vocabulary for temporal patterns.