- Basic Concepts: Retrograde Motion of the Planets - Scientific Revolution -
Professor Robert A. Hatch
T H E S C I E N T I
F I C R E V O L U T I O N
RETROGRADE MOTION OF
Dr Robert A. Hatch -
University of Florida
earth, planets in our solar system appear to undergo retrograde motion.
Because we assume the earth moves, that is, that earth rotates daily and
revolves around the sun each year, it follows that the apparent motion
of the planets is the result of several motions. Because we observe
the planets from a moving platform, the apparent motion of the planets
involves their motion as well as the motion of the earth. But
if we affirm our belief in the motion of the earth, we must also acknowledge
that the motion of the earth is far from obvious. Historically, such a
belief is a relatively recent curiosity. One reason is that retrograde
motion can be accounted for in a number of ways consistent with observation,
common sense, and accurate prediction. Below are two animated illustrations
showing how the apparent retrograde motion of the planets can be described.
The first illustration is a heliocentric (sun- centered) model, a view
traditionally associated with Nicolas Copernicus (1473-1543). The
second illustration is a geocentric (earth-centered) model, traditionally
associated with Claudius Ptolemy (fl. 140 AD).
All Rights Reserved