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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: September 13 Earth's Equatorial Bulge
Message-ID: <708@utastro.UUCP>
Date: Fri, 13-Sep-85 02:00:29 EDT
Article-I.D.: utastro.708
Posted: Fri Sep 13 02:00:29 1985
Date-Received: Sun, 15-Sep-85 05:35:34 EDT
Organization: U. Texas, Astronomy, Austin, TX
Lines: 37

Our planet Earth bulges around its equator.  We'll tell you why --
after this.

September 13  Earth's Equatorial Bulge

There are mountains on Earth -- but they're tiny compared to the
massive bulk of the Earth itself.  If you could shrink Earth to the
size of a billiard ball, its mountains would appear so small that a
real billiard ball would look lumpy in comparison.

As a whole, the Earth is very smooth.  But it isn't perfectly round.
Earth's equator is about thirteen miles farther from the center of
Earth than the north or south pole.  This effect gives Earth a bulge
called the "equatorial bulge." It's caused by the rotation of the
Earth.

Earth rotates once every 24 hours.  No matter where you stand on the
planet, you'll make one complete spin in that same amount of time.

But depending on where you are, you move faster or slower to complete
that one single spin.  Suppose you're standing only a few miles from
the north or south pole.  You'll make the 24-hour circuit alright --
but you won't travel as fast as someone standing at the equator.
You'll have a shorter distance to cover -- and your part of the globe
will be moving more slowly.

At the equator, people make a 25-thousand-mile circuit in 24 hours.
They're traveling at a speed of just over one thousand miles per hour.

So it's no wonder Earth bulges!  Just as a ball attached to a rubber
string stretches when you whirl it around your head -- so the bulk of
the Earth stretches where it rotates the fastest.


Script by Deborah Byrd.

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


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