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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: April 5 Spring Tides
Message-ID: <43@utastro.UUCP>
Date: Fri, 5-Apr-85 02:00:31 EST
Article-I.D.: utastro.43
Posted: Fri Apr  5 02:00:31 1985
Date-Received: Sun, 7-Apr-85 08:59:07 EST
Organization: U. Texas, Astronomy, Austin, TX
Lines: 39


People who live near the ocean may see some especially high tides
today.  More on why -- after this.

April 5  Spring Tides

You may have heard the expression "spring tides." Well, this is spring
-- and we may have some spring tides along the coastlines of our planet
Earth today.  But actually these tides have nothing to do with the
season.

The expression spring tides comes from the root word springen which
means "to leap up." A spring tide can come at any time of year.  It's a
especially high tide -- caused by the sun and the moon.

In general, the moon's gravity causes the tides.  The closer the moon
is to the Earth, the harder its gravity pulls.  The moon's orbit isn't
perfectly circular -- so once each month the moon reaches a closest
point to our world -- called the moon's perigee -- a word that actually
means "near the Earth."

It so happens that the moon is at perigee today -- and that fact
contributes to today's high spring tides.  But there's something else
causing the high tides -- the fact that the moon also reaches the crest
of its full phase today.  You may have noticed a very full looking moon
in the sky last night.  It'll be there again when the sun goes down
Friday evening.

A full moon at perigee is a prescription for very high spring tides --
because a full moon is opposite the sun in space -- or lined up in
space with the Earth and sun.  During such a time, the gravity of the
sun comes into play, too -- causing tides that are higher than usual --
which some of you who live near the ocean may notice.


Script by Deborah Byrd.


(c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin