Seasonal Views of the Earth


 Earth Orbital Eccentricity
 e = 0.01672

 Mean Earth/Sun Distance
 MeanDist = 149.6 Mkm = 92.96 Mmi


 Minimum Earth/Sun Distance
 MinDist = 147.1 Mkm = 91.40 Mmi = MeanDist * (1 - e)

 Maximum Earth/Sun Distance
 MaxDist = 152.1 Mkm = 94.51 Mmi = MeanDist * (1 + e)

 Difference = (Max - Min) = 5.0 Mkm = 3.11 Mmi


General Temperature vs. The Sun/Earth Distance

At any given moment, any season in the northern hemisphere is the direct opposite of the season in the southern hemisphere.  For example, when it is winter in New York City, it is summer in Sydney, Australia and vice versa.

The Earth/Sun distance varies by 3.11 million miles (5.00 Mkm) during the year.  It is during early winter in the northern hemisphere (during the first week in January) that the Earth is closest to the sun than at any other time of the year.  However, in the north, for example, Quebec, Canada, it is generally quite chilly in the beginning of January, despite the Earth being 3.11 million miles (5 million km) closer to the sun than it is in July.  In Australia, it is quite cool (winter) in July, even though the Earth is 3.11 million miles (5.00 Mkm) closer to the sun than it is in January.

Despite the variations in the orbital distance, the general temperatures that we experience during the progress of the seasons, especially in the temperate zones is not strongly influenced by this variation in distance between the Earth and sun.  The primary reason for the significant temperature differences is our thick atmosphere and the varying obliqueness of the angle of the sunlight we receive at midday throughout the year.  Other things, such as atmospheric dust, such as might result from volcanic activity, can also considerably effect seasonal temperatures, sometimes in the extreme.

During the summer months, the sun is higher overhead at midday, where we receive its most direct light and heat, than it is during the winter months.  During the winter months is when the sun is at its lowest in the sky during midday, so sunlight is coming down from a much lower angle than in the summer, so the air is much cooler.

The general rule is:  The lower the midday altitude of the sun, the greater the amount of atmosphere through which the sunlight must pass and the less the heat we receive during the day.


In all the illustrations below, the Earth is viewed edge-on with north upward.  The eye is aligned with the equator running horizontally across the center with the apparent rotation direction being from left to right or counterclockwise with respect to the north pole.


These diagrams illustrate the relative equatorial orientation of
the Earth with respect to the sun on the advent of each season.


On the first day of northern spring and southern autumn, the sun shines down upon the Earth from directly above the equator, moving slowly from south to north, a little more each day.  It will cross the equator again, six month later, in September, on the opposite side of the Earth's orbit.




On the first day of northern summer and southern winter, the sun reaches its greatest northern latitude of about +23.45 degrees, also called the Tropic of Cancer.  On the following day, the sun then starts slowly moving southwards again, a little more each day.




On the first day of northern autumn and southern spring, the sun once again shines down upon the Earth from directly above the equator, as it did six months earlier, in March, on the opposite side of its orbit, only this time, moving slowly from north to south a little more each day.




On the first day of northern winter and southern summer, the sun reaches its greatest southern latitude of about -23.45 degrees, also called the Tropic of Capricorn.  The sun then starts slowly moving northwards again, a little more each day.
And then the cycle of the seasons repeats, ad infinitum.

© Jay Tanner - 2011
Illustrations made using POV-Ray
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