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The distinction is not absolute, because crepuscular animals may also be active on a bright moonlit night or on a dull day. Some animals casually described as nocturnal are in fact crepuscular. [2] Special classes of crepuscular behaviour include matutinal, or "matinal", animals active only in the dawn, and vespertine, only in the dusk.
Vespertine behaviour is a special case of crepuscular behaviour; like crepuscular activity, vespertine activity is limited to dusk rather than full darkness. Unlike vespertine activity, crepuscular activity may resume in dim twilight before dawn. A related term is matutinal, referring to activity limited to the dawn twilight.
It may be argued that if the goal is to avoid human activity, or any other diurnal predator's activity, a nocturnal schedule would be safer. However, many of these animals depend on sight, so a matutinal or crepuscular schedule is especially advantageous as it allows animals to both avoid predation, and have sufficient light to mate and forage. [4]
The lion is a cathemeral felid. Cathemerality, sometimes called "metaturnality", is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are undertaken. [1]
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Pr converts to Pfr during the day time and Pfr slowly reverts to Pr during the night time. When nights are short, an excess amount of Pfr remains in the day time and during long nights, most of the Pfr is reverted to Pr.
Crepuscular rays can also occasionally be viewed underwater, particularly in arctic areas, appearing from ice shelves or cracks in the ice. Also they are also viewed in days when the sun hits the clouds in a perfect angle shining upon the area. There are three primary forms of crepuscular rays [citation needed]:
Crepuscular rays are noticeable when the contrast between light and dark is most obvious. Crepuscular comes from the Latin word crepusculum, meaning "twilight". [2] Crepuscular rays usually appear orange because the path through the atmosphere at dawn and dusk passes through up to 40 times as much air as rays from a high Sun at noon.