dipper@utastro.UUCP (Debbie Byrd) (03/20/85)
Today is the vernal equinox -- the first day of spring. More on the passage of the seasons -- after this. March 20 The Vernal Equinox We live on a planet that tilts as it spins in space. If we lived on a planet that DIDN'T tilt on its axis -- that was upright in its relationship to its movement around the sun -- then we wouldn't celebrate the first day of spring today. If our planet didn't tilt -- every day would be like today. Every day would have twelve hours of daylight and twelve hours of darkness as Earth spun like an upright top, around and around in space. Every day the sun would appear to rise exactly in the east -- and set exactly in the west -- as it does today, the day of the equinox. But the Earth DOES tilt -- by 23 and a half degrees -- with respect to the plane of its orbit around the sun. So for part of the year one pole of the Earth points away from the sun -- the sun from Earth is seen crossing low in the sky -- and that hemisphere enjoys shorter days and the season of winter. Meanwhile, the reverse is true for the other hemisphere. Its pole points toward the sun -- the sun takes the high road across the sky -- and that hemisphere has summer. Right now our friends who live down under -- in the southern hemisphere -- are celebrating the first day of autumn. They experience the seasons at different times than we do -- but share our sense of seasons passing by -- all because we live on a planet that tilts. Script by Diana Hadley and Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin
gwhawkins@watrose.UUCP (gwhawkins) (03/22/85)
One thing to note is that although all areas of the world experience seasons of some kind, the Spring-Summer-Fall-Winter stuff is NOT common to the whole world. India, for instance experiences Rainy and Dry seasons. larry fast (University of Waterloo) broadcasting from exile