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Re: Eratosthenes and plumb bobs

At 13:51 -0600 6/6/01, Rondo JEFFERY wrote:

We had a speaker on our campus a few years ago, I am embarrassed t=
o admit, who was the president of the Flat Earth Society. (He died r=
ecently, by the way. His name was Charles Johnson.) He was invited =
to campus by the science student senator as the main speaker for scie=
nce emphasis week. Needless to say, the faculty were not happy. But=
, that said, I must add that this experience has provided endless opp=
ortunity for those of us who teach gen ed physics, astronomy, and I s=
uppose other subjects, to discuss the importance of knowing some basi=
c facts about the world they live in and how easy it is to prove, or =
verify, some of those basic facts, so you're not persuaded by bogus a=
rguments like those of the Flat Earth Society. (Or the recent FOX 'm=
oon landing hoax' TV show !)

This guy was interviewed by CNN on the occasion of the Rutan/Yeager
non-stop arround the world flight back in the 80's. He, of course,
said that either they had fooled themseves, and had just flown in a
big circle above the flat earth, or that the whole thing was a hoax,
as were the moon landings.

I hope that he was asked many penetrating questions while he was on
your campus.


I happened to be =
in Tucson, AZ, and one evening was looking at the stars, finding what=
was familiar. I found Polaris, the pole star, and using the only an=
gle measuring instrument at hand, my hand, I estimated the angle from=
the north point on the horizon up to Polaris to be a little over 1-1=
/2 hand spans. (The hand span at arms length is about 20 degrees for=
most people. Mine is just slightly over that.) When I got back to=
my home in Roy, Utah (near Ogden) the next night, I did the experime=
nt again and found that Polaris was just over two hand spans above th=
e horizon. The difference in latitude between Tucson, AZ, and Roy, U=
T, was thus a little under 10 degrees, by my crude measurement. Now,=
such an observation proves that the earth is round. To estimate the=
circumerence, the details, I had to get the north-south distance bet=
ween the two cities from an atlas (and yields something over 20,000 m=
iles, not bad for such a crude measurement). But, the fact of differ=
ent elevation angles for Polaris between those two cities proves that=
we live on a curved planet.

Of course, this "proof" is dependent on the assumption that Polaris
is a great distance from the earth, so that moving terrestrial
distances on a true Euclidean plane will not change the relative
elevation of the star (wo the sun, as well, in the case of the
Eratosthenes expt.), something that the flat earth adherents do not
accept. In fact, they will tell you that far from showing the
circumfirence of the earth, it will show the distance to Polaris.
That this method gives the same value for all stars and the sun as
well doesn't bother them since they believe that they all lie on the
same shell of the firmament, and therefore are all the same short
distance away.

Although we should never allow people like flat earthers,
terracentrists or creationists, or any of that ilk go unchallenged,
it is futile to expect that you will change any of their minds. The
benefit of the challenge is to the students who must learn the
elements of critical thinking, and the best way to do that is to
learn how to challenge the people who hold these bizarre (in our
modern owrld, at least) ideas. And the best way to challenge them is
to have the facts at hand (and their source) with which to mount the
challenges. You can't argue with them if you don't know anything.

It is important in our classes that the students be repeatedly
challenged to give support for their ideas, even if they seem
obvious. It is instructive to ask your class how many believe the
earth is round (usually 100%) and how many of them can offer any but
authoritative evidence (it says so in the book; my teacher said so,
etc.) for it (often far fewer than 100%). It is also a good idea to
show them how we have come to know all of these things about the
earth and the solar system and the rest of the universe that they
read about in the newspapers or hear about on TV. Knowing something
as simple as the earth-sun distance, or the solar mass, or the
distances to the stars, or even knowing how we know that the earth
orbits the sun and not vice-versa, can be very liberating for the
students, when they realize that this information is *not* holy writ,
but something that mere humans (including them) can and have
measured. It also introduces them to an appreciation of the iherent
uncertainties in many of these measurements, as well as the modern
techniques that have enabled us to measure some of them with
unprecedented precision.


Hugh Haskell

(919) 467-7610

Let's face it. People use a Mac because they want to, Windows because they
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