rotation of the earth

Don Page (
Fri, 12 Dec 1997 10:20:22 -0700

Glenn, I noticed what appears to be a minor error in something you
wrote several months ago, though it raises some historical questions that I
am curious about.

I followed the advice of Loren Haarsma Wed, 10 Dec 1997 20:43:42
-0500 (EST) and looked up
The first part (not the part Loren referred to) is quoted here:

Date: Mon, 17 Apr 1995 22:24:09 -0400
Subject: Nature vs. Scripture
Message-Id: <>

Bill Crouse wrote:

" Hugh Ross on more than one occasion claims natural
revelation is on par with Scripture (note the cap), and when one
is trained in Biblical exegesis, it is obvious when one reads his
work which becomes the final authority and which must be
subservient to the other. I often observe a similar methodology
on the reflector."

You are presenting what has been biggest point of tension throughout my
Christian life. A look at history shows that exegesis has had a poor record
of allowing the faithful incorporation of observational data into
Christianity. On Wednesday,July 9, 1522 the ship, Victoria, dropped anchor at
Sao Tiago, Cape Verde Islands. When the crew landed they were told that it
was not Wednesday July 9, but Thursday July 10! The ship had been on a 3
year expedition and had kept two independent records of each day. The crew
was sure that they were correct, but the islanders were equally sure. After
much discussion, it was decided that the ship, the sole survivor of
Magellan's voyage, had traveled around the world in the direction that the
earth was rotating. Here was proof that the earth was rotating on its axis.
The religious authorities citing very firmly their training in exegesis and
knowledge of the Scriptures were convinced that the Bible stated that the
earth did not move. Thus the pope ruled that the scientific observation made
by the crew of the Victoria was erroneous. This event was 20 years or so
prior to the publication by Copernicus of his heliocentric theory. 300 years
would pass before the Popes changed their mind. Today we Christians have no
problem with a rotating earth. What changed? What changed was that
observations in Nature became "the final authority" and the interpretation of
those troublesome verses was altered. [End of quote]

Glenn, the same observation would have been made if the earth were
not rotating but the sun were going around the earth, since in that case the
ship would have gone around the earth in the same direction as the sun and
thus seen one fewer sunrise than the islanders who stayed fixed. Given
enough people considering this question, and enough time (which I realize
that you would not have had on this particular issue, since you write so
prolifically), I'm sure that those in the 16th century (particularly those
who really believed that the sun went around the earth) would have realized
that this datum was consistent both with rotation of the earth and a fixed
sun, and with a fixed earth and rotation of the sun around the earth.

Of course, it seems that this datum would have hard to reconcile
with a theory of a flat earth, so those who supported that view would no
doubt have felt threatened. But I was under the impression that the
intellectuals of the day were quite convinced by even the Greek arguments
and evidence for a round earth, and I thought that one of the objections to
granting money for Columbus to try to sail to India was that it was known
that the earth was so large that he would not likely be able to get there on
a reasonable budget.

So I am curious as to what the evidence from the voyage of
Magellan's surviving crew did convince the church authorities. On what
issue and how did they change their minds?

On a more tangential issue, the Greek evidence for the magnitude of
the curvature of the earth came from the position of the sun overhead at two
places in modern Egypt, with a runner (graduate student?) hired to pace off
the distance. (I'm terrible at remembering the details.) This would have
given the curvature in the north-south direction, but until accurate
chronometers were developed (or until Magellan's voyage made some estimate
of how far they traveled east-west in going around the world), I doubt that
there would have been a good way to estimate the curvature east-west. So I
am curious as to whether anyone would have considered the possibility that
the earth were highly prolate or oblate, or maybe some other shape. (Once
Newton's theory of gravity was developed, one could estimate the oblateness
from the earth's rotation, which is small, but this came later.) The Greeks
noticed that the shadow of the earth on the moon during an eclipse was
round, but I have no idea as to whether this did or could have given much
evidence against the possibility of a highly prolate or oblate earth.

There was also the fact that error analysis had not been developed,
so the Greeks by attempting to measure the time differences between first
and final quarter moon and between final and first quarter moon came up with
an estimate of the earth-sun distance that was far too small: They did not
realize that their error in measuring the difference between these two
half-month periods was much greater than the actual difference, and no one
had the accuracy necessary to determine the earth-sun distance until
post-Newton times.

Don Page