ASTR101
Unit 4 Assessment
Answer Key
1. Copernicus—Reintroduced the heliocentric model of the universe.
Brahe—Compiled decades of data on the locations of planets in the sky.
Kepler—Determined the orbits for the planets around the sun and showed that they
were correct by comparing calculations based on his model with the data of Brahe.
Galileo—Made important telescopic observations on the nature of the universe, many of
which undermined the geocentric model. He also developed an approach to the study
of nature which we now call the scientific method.
Newton—Invented the calculus and developed the equations governing motion and
gravity.
2. Kepler determined the orbits by trial and error. He had no theory to work from; he
would just guess and then compare calculations based on his guess with Brahe’s data.
Newton used his theories of motion and gravity to calculate the orbits.
3. Newton’s theory said that objects exert an attractive force on one another in direct
proportion to the product of their masses and inversely proportional to the square of the
distance between their centers. It is called universal because it applies not only to our
solar system but to the entire universe.
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