托福听力段子8.理科段子:天文学
In ancient times, many people believed the
earth was a flat disc. Well over 2,000 years ago; the ancient Greek
philosophers were able to put forward two good arguments proving
that it was not. Direct observations of heavenly bodies were the
basis of both these arguments. First, the Greeks knew that during
eclipses of the moon the earth was between the sun and the moon,
and they saw that during these eclipses, the
earth’s shadow on the
moon was always round, they realized that this could be true only
if the earth was spherical, It the earth was a flat disc, then its
shadow during eclipses would not be a prefect circle; it would be
stretched out into a long ellipse. The second argument was based on
what the Greeks saw during their travels. They noticed that the
North Star, or Polaris, appeared lower in the sky when they
traveled south, in the more northerly regions, the North Star
appeared to them to be much higher in the sky. By the way, it was
also from this difference in the apparent position of the North
Star that the Greeks first calculated the approximate distance
around the circumference of the earth, a figure recorded in ancient
documents says 400.000 stadium, that’s the plural of the world stadium. Today,
it’s not known exactly
what length one stadium represents, but let’s say it was about 200 meters, the length
of many athletic stadiums. This would make the
Greek’s estimate about
twice the figure accepted today, a very good estimate for those
writing so long before even the first telescope was invented.
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