AST 201S - Stars and Galaxies
University of Toronto Mississauga
Chapter 3 Summary
Essential Cosmic Evolution, 5 Edition th
(NOTE: In Chapter 4 we will return to Chapter 3 and use a few more of the topics).
1. The concept of the scientiﬁc “model” - how we imagine or picture in our mind a
distant astronomical object
2. Developed by Greek scientists more than 2000 years ago, based on logic and natural
3. Examples of astronomical models:
• The geocentric model of the solar system developed by Ptolemy.
• The heliocentric model of the solar system revived by Copernicus.
4. The scientiﬁc method
• observe something that attracts our attention
Example: the sudden appearance of a new star in a constellation
• make up an explanation = model - a creative act. This is like being a detective
Example: explain the new star in the constellation as being a faint star that
exploded and became much brighter
• use our experience from Earth (all our sciences) to ﬁll in our model - this makes