Astronomy as a Science
Goals and key points:
Understand the development of Astronomy as a science through an overview of the Copernican
+Astronomy as a science
-Ancient civilizations have always used astronomy. Ex. marking the seasons, navigation etc.
-Astronomy as a science has roots in many ancient cultures. Familiar example: Greece
-Measuring the circumference of the Earth in 240 BC:
Syene to Alexandria: distance = 5000 stadia angle = 7 degrees
7/360 × (Earth circum.) = 5000 stadia
Earth circum. = 5000 stadia × 360/7 = 250 000 stadia
1 stadia ~ 1/6 kilometers
Earth circum. = 42 000 kilometers (actual value is 40 075 kilometers)
-The Greeks were among the first to make mathematical models of nature.
They attempted to explain patterns without the use of supernatural intervention.
-The Greek model of the Universe underpinning of the model:
• Earth is at the center (geocentric)
• Heavens must be perfect (spheres etc)
This was driven by evidence and philosophy
• The Sun, stars and planets appear to move around the Earth
• No perceptible movement of the Earth
• They insisted on mathematical perfection (whole numbers, perfect spheres, musical scales
• This insistence eventually lead to stagnant models and a refusal to change in the face of
new evidence. -Ptolemy’s model (150 A.D.)
The complex motions of the planets are difficult to explain within the geocentric model.
Retrograde motion: Planets usually appear to move E to W but occasionally reverse direction
(W to E). (Chapter 2, section 2.4)