semidiurnális

Semidiurnal is an adjective used in astronomy and biology to describe phenomena that occur twice a day, typically at approximately equal intervals. The term is derived from the Latin words "semi," meaning half, and "diurnalis," meaning daily. In astronomy, semidiurnal tides are tidal cycles that occur twice daily, with the high and low tides being approximately 12 hours apart. This is in contrast to diurnal tides, which occur once daily, and mixed tides, which occur more than twice daily.

In biology, semidiurnal refers to the activity patterns of organisms that are active twice a day, usually at dawn and dusk. This pattern is common among nocturnal animals that need to avoid predators during the day. Examples include certain species of bats, birds, and insects. The semidiurnal rhythm is a form of circadian rhythm, which is the internal biological clock that regulates various physiological processes.

The semidiurnal pattern is also observed in some human activities, such as sleep-wake cycles and meal times, although these are typically not as strictly regulated as in animals. The semidiurnal rhythm is an important concept in the study of both natural and human phenomena, providing insights into the timing and frequency of various biological and astronomical events.