Tomorrow (Sept. 22) at 11:09 p.m., Eastern Daylight Time, the center of the sun will cross Earth's equator, marking the autumnal equinox, and the start of fall in the Northern Hemisphere.
For a brief period, days and nights around the world each last close to 12 hours (day and night are not exactly equal, as the term "equinox" is meant to imply). Then, as the Earth continues its path around the sun, days become shorter and nights lengthen, with the change becoming more pronounced in the higher latitudes, but remaining nonexistent at the equator.
This change in the amount of light is a signal to animals, plants and, before the light bulb, people, of changing seasons. For some creatures living at high latitudes, it can have a profound effect on their biology, particularly on reproduction, which must be carefully timed.
For instance, during long winter days, the Siberian hamsters' testes increase to almost 17 times their size during short days. And there is evidence that song birds living near sources of artificial light begin singing to attract mates, as well as laying eggs, earlier in the spring than their counterparts in places that remain dark at night.
more How Change of Seasons Affects Animals and Humans - Yahoo! News
For a brief period, days and nights around the world each last close to 12 hours (day and night are not exactly equal, as the term "equinox" is meant to imply). Then, as the Earth continues its path around the sun, days become shorter and nights lengthen, with the change becoming more pronounced in the higher latitudes, but remaining nonexistent at the equator.
This change in the amount of light is a signal to animals, plants and, before the light bulb, people, of changing seasons. For some creatures living at high latitudes, it can have a profound effect on their biology, particularly on reproduction, which must be carefully timed.
For instance, during long winter days, the Siberian hamsters' testes increase to almost 17 times their size during short days. And there is evidence that song birds living near sources of artificial light begin singing to attract mates, as well as laying eggs, earlier in the spring than their counterparts in places that remain dark at night.
more How Change of Seasons Affects Animals and Humans - Yahoo! News