This part is wrong.the different seasons, caused by how far and how close the earth gets to the sun.
The seasons are caused by the earth's axialtilt, the angle by which its axis deviates from the perpendicular to the plane in which it orbits the sun. Thus, the north pole tilts toward the sun in one part of the orbit, and on the other side, six months later, the north pole will be tilting away from it as the south pole tilts toward it.
The earth orbits the sun in an ellipse, with the sun at one of its foci. This means that the earth is closest to the sun once a year. It turns out that the south pole is pointing at the sun at this time, and getting its maximal sun exposure. This is summer for the southern hemisphere. The northern hemisphere gets its fullest sun six months later when the earth is as far from the sun as possible - its summer. Thus the seasons depend on the tilt, and NOT the distance from the sun. If you live in the northern hemisphere, your summer comes when the earth is furthest from the sun, not closest.
This illustration is labeled from a northern hemispheric perspective: http://oceanworld.tamu.edu/resources/ocng_tex... Note that when the earth is closest to the sun, it is winter in the northern hemisphere because the north pole is tiled away from the sun. That is the southern hemisphere's summer.
Thus, distance from the sun is not as important a factor as the angle and direction of the earth's axial tilt.
Interestingly, the angle of the axial tilt, presently 23.44° from perpendicular varies between 22.1 degrees at its minimum to 24.5 degrees at the maximum over a 41,000 year cycle. The more upright the earth, the less extreme the seasons.
Furthermore, at the same time, the earth is precessing like a top over a 26,000 year cycle, which moves the date of the solstice (see precession of the equinoxes). In 13,000 years, the earth's north pole will no longer be pointing at the northern star (polaris), and summer will occur for the northern hemisphere when it is closest ti the sun, not furthest as is the case presently. http://ancientegypt.hypermart.net/royalarch/
And believe it or not, both the orientation of the earth's elliptical orbit and its degree of eccentricity - its departure from perfect circularity - also cycle.
The first of these is called the earth's anomalistic precession, or advancing of the perihelion. http://www.daviddarling.info/images/perihelio... This cycle occurs over about 112,000 years.
The eccentricity of the earth's orbit varies from a minimum of .0034 (zero means perfect circularity) to a maximum of 0.0580 (mean eccentricity is 0.0280) and back again over a period of 413,000 years.
Who knew, huh?