cjh (11/10/82)
In response to your message of Mon Nov 1 15:38:22 1982: Basically, seasons on this planet are caused not by proximity to the sun (which varies by only 1-2% over a year) but by the fact that the earth's axis of rotation is not perpendicular to the plane of its orbit but is tilted ca. 23 1/3 degrees. This tilt would appear constant as the earth goes around the sun to someone observing from outside the solar system. The seasons are caused by the variance in the distance the suns' rays have to plow through the atmosphere; when the nearer pole is tilted toward the sun the rays are closer to perpendicular to the ground: summer winter | * *----| \ | * = sun's image at top of atmosphere | \ | | = ground \ | \| The axial tilt also gives rise to amusing phenomena like the "midnight sun" (if you're close enough to the summer pole the sun will dip but not disappear) and the inversion of seasons in the southern hemisphere (according to a UN children's book I remember, Australians are likely to get surfboards rather than sleds for Christmas). The variation in distance does currently make the southern seasons more vigorous and the northern seasons more temperate; I don't know how fast the orbit precesses (the poles describe a circle every ~23,000 years) so I can't say how/when this will change.