74 PART 1^ |^ EXPLORING THE SKY
- Galileo’s telescopes were not of high quality by modern standards. He
was able to see the moons of Jupiter, but he never reported seeing
features on Mars. Use the small-angle formula to fi nd the angular
diameter of Mars when it is closest to Earth. How does that compare
with the maximum angular diameter of Jupiter?
Learning to Look
- Study Figure 4-11 and describe the phases that Venus would have
displayed to Galileo’s telescope if the Tychonic universe had been
correct. - What three astronomical objects are represented here? What are the
two rings? - Use the fi gure below to explain how the Ptolemaic model treated some
planets differently from the rest. How did the Copernican model treat all
of the planets the same?
Discussion Questions
- Historian of science Thomas Kuhn has said that De Revolutionibus was
a revolution-making book but not a revolutionary book. How was it an
old-fashioned, classical book? - Why might Tycho Brahe have hesitated to hire Kepler? Why do you
suppose he appointed Kepler his scientifi c heir? - How does the modern controversy over creationism and evolution
refl ect two ways of knowing about the physical world?
Problems
- Draw and label a diagram of the eastern horizon from northeast to
southeast and label the rising point of the sun at the solstices and
equinoxes. (See page 19 and Figure 4-1.) - If you lived on Mars, which planets would exhibit retrograde motion?
Which would never be visible as crescent phases? - If a planet has an average distance from the sun of 4 AU, what is its
orbital period? - If a space probe is sent into an orbit around the sun that brings it
as close as 0.5 AU and as far away as 5.5 AU, what will be its orbital
period? - Neptune orbits the sun with a period of 164.8 years. What is its
average distance from the sun? - Galileo’s telescope showed him that Venus has a large angular
diameter (61 arc seconds) when it is a crescent and a small angular
diameter (10 arc seconds) when it is nearly full. Use the small-angle
formula to fi nd the ratio of its maximum distance to its minimum
distance. Is this ratio compatible with the Ptolemaic universe shown
on page 57?