All of Chapter 3 & 4 Includes information abou Tycho Brahe and Galellio

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Published on 16 Oct 2011
School
York University
Department
Natural Science
Course
NATS 1745
NATS 1745 History of Astronomy November 2, 2010
Planetary Motion
Sidereal period: time for a planet to complete 1 orbit with respect to the
stars (a.k.a orbital period)
Synodic period: time for a planet to return to the same position relative to
the Sun, as seen from Earth.
Sidereal period takes 225 days to
go around Venus.
We observe the synodic period,
more than we use the sidereal period.
Synodic takes 584 days to go around
Venus.
Apparent Motion: the motion of a celestial body across the sky.
Angular speed: the angle of sky a planet traverses in a given amount of
time.
We see the speeds of other planets the same time we see the speeds of
other cars highway driving.
Features of Apparent planetary motion:
o Planets display both forward motion (aka direct: W
E) and
backward motion (aka retrograde: E
W)
o A planet’s angular speed is not constant (planets slow down and
speed up in the sky)
By tracking them from night to night you see that their angular speeds are
NOT constant
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Document Summary

Sidereal period: time for a planet to complete 1 orbit with respect to the stars (a. k. a orbital period) Synodic period: time for a planet to return to the same position relative to the sun, as seen from earth. Sidereal period takes 225 days to go around venus. We observe the synodic period, more than we use the sidereal period. Apparent motion: the motion of a celestial body across the sky. Angular speed: the angle of sky a planet traverses in a given amount of time. We see the speeds of other planets the same time we see the speeds of other cars highway driving. By tracking them from night to night you see that their angular speeds are. Eudoxus came up with a model, which shows how to explain the planetary. The sum of the two components of motion, create a figure-8.