The Heavenly Cycles

And the Moon in haste eclipsed her And the Sun in anger swore

He would curl his wick within him

And give light to you no more.

Aristophanes, The Chorus of Clouds

Our life rhythms are controlled by the heavenly cycles: the daily rising and setting of the Sun, the monthly variation in the brightness of the Moon, and the seasonal north—south displacement of the Sun affecting the influx of solar power and thus the climate.

It does not necessarily follow that all plants and animals have identical tempos. For any cyclic phenomenon, scientists may speak of both its frequency (the number of times it occurs within a given time, or equivalently its period, the duration of the cycle), and also its phase. Football games, for example, are played once a week (the frequency), making the period seven days, but there are different phases depending upon the level involved: high schools tend to play on Friday evenings, college matches are on Saturday afternoons, and professional games on Sundays.

In the natural world most organisms follow a basic daily cycle, although their phases may differ. The majority of animals go about their business during daylight hours, but there are many specialized nocturnal beasts, too. (To go back to our football metaphor, there are also a few games on Monday or Thursday nights.) In addition, not all animals follow 24-hour cycles, as we will see.

Turning to the yearly cycle, the changing levels of daylight and temperature influence us all, and more so at extreme latitudes rather than the tropical zones where intra-annual variations are minimized. Who can claim that they are not affected in any way by the seasons, if only through oscillations in the price of fresh foods? Other animals suffer more radical alterations in food availability during the year, which exert greater control over their lives. In consequence many species hibernate during the winter, emerging only when the signs of spring promise plenty of food, telling them it is time to eat and breed again.

Telescopes Mastery

Telescopes Mastery

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