6
Aristotle’s
Universe: Earth’s Shape
•Aristotle knew the Earth was round:
– Shadow of Earth during lunar
eclipse
–Changing height of
Polaris and celestial pole as you moved south
•Eratosthenes measured size of Earth
to better than 20%
to better than 20%
–~200
BC, Greek living in Alexandria
Egypt
–Observed
that
•Sun was
overhead at Syene on summer solstice
•Sun was 7o to the south
of zenith at Alexandria
–Circumference of Earth must be 360/7 times
distance from Syene to Alexandria
distance from Syene to Alexandria
From Voyages by Fraknoi et al.
From our text:
Horizons, by Seeds