dipper@utastro.UUCP (Debbie Byrd) (10/17/85)
Mars has seasons -- just as Earth does. But there the seasons change more dramatically than on Earth. More -- after this. October 17 Mars at Aphelion The planet Mars is a cold but beautiful desert -- rocky and red. Today it is especially cold in the southern hemisphere of Mars -- because today Mars is at aphelion, its farthest point from the sun. Like Earth, Mars tilts on its axis -- and this tilt, not the distance to the sun, causes the change in the martian seasons. But Earth's orbit around the sun is nearly circular, while the orbit of Mars is more elliptical -- more like a circle that's been squashed. Changes in the distance between Mars and the sun are great enough to affect the temperature on the red planet. On Mars right now, it's winter in the martian southern hemisphere. And today Mars is farthest from the sun. So the southern winter is even colder than it would otherwise be. In the martian southern hemisphere today, temperatures probably are plunging to around 200 degrees below zero. Meanwhile, the northern hemisphere of Mars is having pleasantly cool summer days -- and moderately cold nights. An Earth-year from now -- half a year later on Mars -- the red planet will be nearest the sun in its orbit. The southern hemisphere will be tipped toward the sun -- and it'll be warm enough in that hemisphere to shrink the south polar cap of Mars. Meanwhile, once again, the northern hemisphere will be having milder weather. Throughout the martian year, the changing distance between Mars and the sun amplifies the change in the seasons -- so that the southern hemisphere freezes and bakes -- while the martian northern hemisphere experiences only mild changes. Script by Holly Clark. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin