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Why there are summer and winter seasons?

  1. Dec 6, 2015 #1
    Hello guys, can someone explain me the four seasons ? Why they repeat in same intervals every year ? I think of this:

    Thanks Untitled-1.png
  2. jcsd
  3. Dec 6, 2015 #2


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    That picture is not the reason for the seasons (at least, not the whole story).

    In fact, in the northern hemisphere, winter is just getting started when the earth passes thru the perihelion (closest approach to the sun), somewhere along about January 3 or so. When summer is at its height in July in the northern hemisphere, the earth is passing thru its aphelion (farthest point away from the sun). What is this sorcery?


    It's explained here:

  4. Dec 6, 2015 #3
  5. Dec 6, 2015 #4
    As you suggested, the Earth's orbit is not perfectly circular, but it's not as an extreme elipse as your diagram suggests.
    While that does make some difference to the overall amount of solar radiation arriving on Earth, that effect is vastly less than the effect produced by the Earth's axial tilt.
    The effect of the axial tilt is such that in the northern hemisphere, 'Summer' in the polar regions is 6 months of continuous daylight, and winter is 6 months of darkness.
    The same thing happens at the South pole, but the opposite way around, Summer in the northern hemisphere is winter in the south.
    Outside of the polar regions there are longer days in summer, but the Sun does set for a while every day.
    Last edited: Dec 6, 2015
  6. Dec 6, 2015 #5


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    The orbital eccentricity of the earth is about 0.017, which means that the earth's max. and min distances from the sun differ by about 5 million km (out of about 150 million km average distance)

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