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This maybe simple and usual question, although there is a lot of confusion about it over internet and even in some books, so I want from an astronomer / astrophysicist to fill the gaps for me accurately.

Fixed axis tilt is the reason, this is the most common explanation, but with some research, you will find that it is not the only reason!

Actually, earth distance from the sun playing its role: considering that the received energy from sun is inverse proportional to the square of earth distance, one can calculate that it's contribute to a change by 5-7% of the received energy. Moreover, it's effect is opposite, in senses that because we have summer when we are at the furthest point from sun, this actually reduces summer temperature due to axis tilt.

Also I read a claim that mentions a third reason, that most of the texts ignores, it is the angle of earth orbit to the suns equator, anyway, I found no quantitative analysis.

Your comments please.

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Orbital eccentricity is unlikely to be a significant component of seasonal temperature variations because this has the same effect in both north and south hemispheres at the same time since the position on the orbit is the same for the whole earth. If ecentricity was the primary cause of seasons, seasons would be the same both hemispheres. Axis tilt being the primary cause of seasons accounts for opposite seasons in north and south hemispheres.

The observable effect of eccentricity should be a difference between corresponding seasons between the hemispheres, eg between northern summer and southern summer temperatures at corresponding latitudes. How the effect manifests also depends on the angle in the orbital plane between the direction of the axis tilt and direction of maximum orbital distance.

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  • $\begingroup$ Your discussion seems to be wrong: "… perihelion in January, and it reaches aphelion in July, so the slight contribution of orbital eccentricity opposes the temperature trends of the seasons in the Northern hemisphere." (wikipedia) so it will do opposite edges in southern hemisphere. $\endgroup$
    – TMS
    May 25, 2014 at 8:52
  • $\begingroup$ I think that paragraph is saying what I am saying. Also the very next paragraph of the same article says "Orbital eccentricity can influence temperatures, but on Earth, this effect is small and is more than counteracted by other factors; research shows that the Earth as a whole is actually slightly warmer when farther from the sun." $\endgroup$ May 25, 2014 at 9:12
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The reason for Seasons is the Tilt and distance from the sun! But, it also depends on the Angle the light comes in from. Also the distance of the Photons apart from each other on earth.

This is probably just a simple answer.

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