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Q & A: Cause of seasonal changes

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Most recent answer: 03/10/2008
Q:
What makes the seasons change? I thought it is the orbit of earth around sun but it seems there are some other reasons also.
- Barga (age 11)
Indiana
A:
The earth goes around the sun in an orbit.  This orbit defines a plane.  Now the earth spins on an axis.  If this axis were perpendicular to the orbital plane, there would be no seasonal changes. However the tilt angle is about 23.5 degrees so, during the summer the Northern hemisphere gets more sunlight than the Southern hemisphere and vice-versa during the winter.
There is a nice article with diagrams that shows this at 
There is an additional small effect due to the fact that the earth's orbit is not quite circular; in fact it is an ellipse.  During part of the orbit the earth is a bit closer to the sun and so gets more heat.  Curiously enough this 'nearest appoach point' occurs around January 2nd.  You can find more information about this at:

LeeH

(published on 03/10/2008)

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