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The Earth is not Flat?

If Not, How Big Is It?



Yes, the earth is round. (More or less)

And it is about 12,700km (7,900 miles) in diameter.

But how do you know this? Does everything have to come from Mummy? (Or Wikipedia). Could you prove the world is round, for yourself? Figure out how big it is?

Yes! You could. With a little help from a friend.

First you need to figure out where south is. "True" south, not magnetic south. (I'll try to say something about the difference one day.)

Then you need a nice flat horizontal surface where the sun shines. On it, you need a line running north and south.

You put up something to throw a shadow. (People call such things "gnomens", not that you "need" the word after you finish this lesson.)

I WILL do a diagram, eventually. For now, sorry...

One end of the gnomen should be on your north/south line, and the other should be directly above it.

Now you wait. You wait until the shadow of the gnomen lies along the north/south line.

At that moment, you measure the length of the shadow. You also measure the height of the gnomen. Let's say that in your case, a 30cm gnomen cast a 30cm shadow.

Then you ask your friend, somewhere more or less directly north of south of you to do the same thing, on the same day, and you exchange your readings. Let's say your friend is south of you. He might have found the gnomen's shadow to be only 28cm, even though his gnomen was also 30cm long.

Now you know the earth is round! And how big it is!

Well... maybe you DON'T know... yet. But the information above "tells" you the earth is round! And if you can figure out a way to know how far south of you your friend is, you now even have enough information to figure out how big the earth is.

But those details will have to come at another time. Write to me if you want the rest of "the answer" sooner.

Good Instrument Design

Did you realize that your level, horizontal, surface... with gnomen... was a "scientific instrument"? Well it was.

How could you design one which would be...

Down the ages, often times the person who could design a great instrument became known as a great scientist.

I will, in due course, give my answers to the above... but what can you think of for yourself?





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