ASTR 101 Lecture Notes - Lecture 6: Depth Perception, Radar Gun, Aberration Of Light
6 Sep 2016
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Chapter 2. 3: the size, shape and motion of the earth. The ancients knew the shape of the earth. Aristotle summarized evidence showing the earth is spherical. First evidence was the behaviour of the stars. Polaris appears to be a fair distance above the northern horizon as seen from athens. Polaris appears to be low on the northern horizon as seen from khartoum, a city south of athens. In general, this dependence of the altitude of the stars upon our position on the globe in the north-south sense tells us that we"re on a curved surface. Second evidence was the behaviour of ships sailing to sea. If the earth was flat, one would see the ship in view at all times; the ship would just get smaller. Since the earth is round, the ship disappears into the distance hull down . Another e. g. : take a picture from 2m above sand and then 12 m above sand.
