As the Earth orbits the sun it follows two motions. One is the spinning
motion around the Earth's own axis. This motion causes the days and
nights. The other motion along the elliptical orbit takes a year to
complete one full rotation around the sun. Seasons are caused by the Earth's axis being
inclined at about 23-1/2o with the orbital plane. As the Earth orbits the sun its axis always points to the same direction.
In December the North Pole is leaning away from the sun and the Northern hemisphere receives less sunlight. The days are short and
the sun is low in the sky so the sunlight is spread thinly over the
Earth's surface. The sun is lowest in the sky on December 22, the winter solstice. The Northern Hemisphere receives so less sunlight that the Earth continues to get colder for another month. Thus January is colder than December. And the coldest time comes about the end of January.
Things just get reverse as we move down to the southern hemisphere across
the Equator.
Thus seasons are defined by this gradual shifting movement between the
summer solstice and winter solstice. As we move on from winter to summer,
or, the other way round, we come across four seasons, distinct especially
in the temperate zones. Moving from the winter, in spring it gets warmer, in summer, hot.
In autumn it gets cooler, in winter cold. Spring comes earlier down in southern areas than farther in the north. This is just the reverse in the southern hemisphere.
Shadows:
As light emitting from a source gets hit by an opaque object a shadow is
created away from the source and on the other side of the object.
Shadows under the sun are created when the sunrays get hit by any opaque
object - living or not. As the sun moves on from east to west shadows are
created. Thus shadows are the longest when the sun is in the east
or, west horizon. At around noon when the sun is perched just overhead,
the shadows get reduced to a minimal length.
The movement of shadow in sync with the sun could be applied in making a
sundial, the earliest form of clock known to give a near perfect
reading.
This shadow movement also changes with the change of season. In winter as
the North Pole leans away from the sun light falls a bit slantingly on the
objects in the North.
Thus shadows are always a little longer throughout the winter days as
against those during the summer. The variation in this shadow movement
also helps us to predict the shifting of the seasons.
Now is it really possible to predict if spring is near or far?
Well, on February the sunlight is already bound for summer as the North
Pole comes nearer the sun. The length of shadow is thus somewhat
shorter, but not remarkably enough. So it is difficult to distinguish
between a late January and a late February shadow unless you are a
keen regular observer.
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