dipper@utastro.UUCP (Debbie Byrd) (11/06/84)
Mars is now at its closest point to the sun. We'll tell you what that means for the seasons on Mars -- right after this. November 6 Mars at Perihelion Tomorrow the planet Mars will reach its perihelion -- or closest point to the sun for this Martian year -- which by the way equals about one year, plus 10-and-a-half months in Earth time. On Earth, perihelion doesn't mean much in terms of the temperature on our world -- because Earth's orbit is more nearly circular -- and our distance from the sun doesn't really change very much. But the orbit of Mars is more eccentric -- and the Martian perihelion do strongly affect the weather on the red planet. The effect is to create moderate seasons for the northern hemisphere of Mars, and extreme ones for the south. Mars is always at perihelion, or nearest the sun, when it's summer in the southern hemisphere. Then the more eccentric orbit of Mars places the planet closer to the sun by a great-enough distance to increase the temperature noticeably. During the southern summer, the Martian south polar cap may appear from Earth to melt entirely away! Meanwhile, the same higher temperatures bestow a mild winter on the Martian northern hemisphere. Less than one Earth-year from now, on October 17, 1985, Mars will be at aphelion, or farthest from the sun. Then it will be summer in the northern hemisphere of Mars -- a cool summer, because of the greater distance between the planet and its mother star. At the same time, the southern hemisphere -- also farthest from the sun -- will be laboring under the brutal cold of a severe Martian winter. Script by Deborah Byrd. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin