Seasonality is intimately related to day length. Instantaneously, half the Earth
has daytime while the other half has nighttime. Yet, the tilt of the Earth’s axis
ensures that day lengths vary by latitude. At the equator, there are 12 hours of day
and 12 hours of night (excluding twilight) throughout the year. If it is the time of
an equinox, all places on Earth have approximately equal day and night periods.
At other times, there is a systematic variation of day length with distance from
the equator. In the winter hemisphere, day lengths get shorter and shorter with
increasing latitude and, poleward of the Arctic or Antarctic Circles there is no
direct sunlight. In the summer hemisphere, day lengths become longer and longer
with increasing latitude and, poleward ofthe Arctic or Antarctic Circles the sun
does not set for increasingly great amounts of time for up to six months.
Though seasonality is based on Earth/sun relationships described above, it is
expressed quite differently overthe globe. Latitudinally, there are three seasonal
temperature zones. In the deep tropics there it is always “summer”—warm to hot.
In the middle latitudes there is a striking winter/summer temperature difference.
In the polar latitudes, temperatures range from winter frigid to summer cold. Pre-
cipitation is also a part of seasonality. Most locations have their peak precipitation300 Seasons
Seasons are experienced at the polar and temperate latitudes due to the tilt of the earth’s axis as it
orbits the sun. The seasons are reversed beween the Northern and Southern hemispheres.
(ABC-CLIO)