Precession
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- The north celestial pole moves in a circle among the stars.
- Currently, Polaris is the star closest to the north celestial pole: the North
Star
- The entire period of precession takes 26,000 years
Retrograde Motion
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The apparent motion of the planets when they appear to move backwards
(westward) which was difficult for astronomers to explain.
The apparent backward motion (E -> W) of a planet with respect to the
, background stars.
Caused by the difference in speed of the planets as they orbit the sun.
Parallax
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An apparent shift in the position of an object when viewed from different
locations. Ancient philosophers did not experience this with the sky so they
concluded the Earth did not move.
Eratosthenes
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. Performed a remarkably accurate computation of the earth's
circumference by using the sunlight shining to the bottom of a well in the
Southern city of Syrene.
Angular distance between Syene and Alexandria: ~ 70
Linear distance between Syene and Alexandria: ~ 5,000 stadia
Earth Radius ~ 40,000 stadia (probably ~ 14 % too large) - better than any
previous radius estimate.
Ptolemy's book "Almagest"
Give this one a try later!
Put Aristotle's model was put to mathematical form, preserving the
principals of geocentricism and uniform circular motion, but adding
epicycles, deferents, and equants. Ptolemey epicycles could approximate
Give this one a try later!
- The north celestial pole moves in a circle among the stars.
- Currently, Polaris is the star closest to the north celestial pole: the North
Star
- The entire period of precession takes 26,000 years
Retrograde Motion
Give this one a try later!
The apparent motion of the planets when they appear to move backwards
(westward) which was difficult for astronomers to explain.
The apparent backward motion (E -> W) of a planet with respect to the
, background stars.
Caused by the difference in speed of the planets as they orbit the sun.
Parallax
Give this one a try later!
An apparent shift in the position of an object when viewed from different
locations. Ancient philosophers did not experience this with the sky so they
concluded the Earth did not move.
Eratosthenes
Give this one a try later!
. Performed a remarkably accurate computation of the earth's
circumference by using the sunlight shining to the bottom of a well in the
Southern city of Syrene.
Angular distance between Syene and Alexandria: ~ 70
Linear distance between Syene and Alexandria: ~ 5,000 stadia
Earth Radius ~ 40,000 stadia (probably ~ 14 % too large) - better than any
previous radius estimate.
Ptolemy's book "Almagest"
Give this one a try later!
Put Aristotle's model was put to mathematical form, preserving the
principals of geocentricism and uniform circular motion, but adding
epicycles, deferents, and equants. Ptolemey epicycles could approximate
