How big is the Earth?
Before Man started pondering over the question, it undoubtedly had been necessary to realize first that Earth was spherical. This can easily be understood during an eclipse of the Moon when one can see that the shadow cast by Earth on the Moon is a portion of a disk.
Aristotle, the famous Greek natural philosopher, reports that mathematicians had allegedly evaluated the dimension of Earth at 40.000 stadia, adding: `From their supposition, it follows that the shape of Earth must be a sphere and also that its size be small relative to the distance of other celestial bodies.'
It was generally agreed upon that measuring the size of Earth could be done by measuring the altitude of a star from two cities situated on the same meridian.
Then, a difference expressed in degrees would be found. If the distance between the two cities was known, from estimates by caravaneers for instance, it would then be possible to find the value of a degree of meridian and hence derive the value of the terrestrial circumference.
The stadium, Aristotle's unit length, apparently corresponds to 185 meters, so the value of 74.000 km thus obtained is much too high. Archimedes, in his treatise De Arenae Numero [On the number of sand grains] quotes a value of 300.000 stadia for the terrestrial circumference. This means that the measurement must have been attempted several times.
> http://http.hq.eso.org/outreach/spec-prog/aol/market/collaboration/erathostenes/
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> the circumference of the earth is
> 40,090 km in equatorial (radius is 6378 km) &
> 39,958 km in polar (radius is 6357 km).
>
> But this website says
> http://rainbow.ldeo.columbia.edu/courses/v1001/fermi.html
>
> it is 24,000 miles (which is 38,400 km) and they claim
> that each time zone has 1,000 miles.
>
> Which 1 is correct.
>
> Madan
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