Name: __________________
Geology Chapter 22 – Origin of Modern Astronomy
Michael Wysession Washington University
Big Ideas Satellites, moons, planets, and stars travel along predictable paths that are determined by the mass of
the objects and the laws of gravity.
Space and Time Many early people believed in a geocentric model of the universe, where all objects revolved
around Earth. The Ptolemaic system adapted the geocentric model to include explanations of the apparent
retrograde motions of planets. Copernicus showed that the heliocentric model, with Earth revolving around the
sun, was simpler. Planets, moons, and satellites follow elliptical orbits when they revolve around another body,
as shown by Kepler.
Forces and Motion Earth rotates once per day. This day is 24 hours with respect to the sun, but 23 hours and
56 minutes with respect to the stars. Earth revolves around the sun once every 365.25 days, or one year. The
seasons are a result of the tilt of Earth's axis of rotation, which is 23.50 with respect to the solar ecliptic. The
direction that Earth's axis points to changes, or precesses, over a period of 26,000 years. The phases of the
moon are a result of the relative positions of the sun, moon, and Earth. Solar and lunar eclipses occur when
these three bodies are lined up.
Matter and Energy The Apollo missions, during which astronauts visited the moon, revealed a great deal
about our nearest neighbor. The moon formed from the ejected debris of an enormous impact of a Mars-sized
planetesimal with Earth early in our planet's history. Because the moon has so little mass, it lacks an
atmosphere, hydrosphere, or biosphere, and so its structure and surface are very different from Earth's.
Section 1 – Early Astronomy
1. Define astronomy.
2. What does astronomy deal with?
3. Who was Aristotle and what did he think the shape of the Earth was?
4. Who was Eratosthenes and what did he do?
5. How big is a stadia?
6. What was Eratosthenes’ calculated Earth circumference and what is it really?
7. Who was Hippachus and what was he famous for?
8. Describe the geocentric model.
9. What is the celestial sphere?
10. Who was the first Greek to believe the heliocentric model?
11. What is the heliocentric model?
12. Who was Claudius Ptolemy and what did he present and what did it account for?
13. What did Copernicus conclude?
14. What did Tycho Brahe do for astronomy?
15. What did Kepler discover?
16. Summarize Kepler’s three laws.
17. What is an astronomical unit (AU)?
18. What was Galileo Galilei’s most important contribution to astronomy?
19. List Galileo’s five discoveries.
20. What is inertia?
21. What idea did Sir Isaac Newton first formulate?
22. According to Newton, every body in the _________________ attracts every other body with a
_________________ that is directly proportional to their _________________ and inversely proportional to
the square of the _________________ between their centers of mass.
23. The law of universal _________________ also states that the greater the _________________ of the object,
the greater is its _________________ force.
24. What is the mass of an object a measure of?
25. How is mass measured?
26. What is the difference between mass and weight?
Section 2 – The Earth-Moon-Sun System
27. What is the difference between rotation and revolution?
28. What is precession?
29. What is the main result of Earth’s rotation?
30. Name two ways of measuring Earth’s rotation?
31. Describe a mean solar day.
32. Describe a sidereal day.
33. How does Earth revolve around the sun?
34. Compare perihelion and aphelion.
35. What is the ecliptic?
36. What is the imaginary plane that connects Earth’s orbit with the celestial sphere?
37. How is Earth’s axis of rotation tilted?
38. What is the result of this tilt?
39. When the apparent position of the _________________ is plotted on the _________________ sphere over a
period of a _________________ time, its path intersects the celestial _________________ at two points.
40. When are these two intersections?
41. Earth’s axis maintains _________________ the same angle of _________________. But the
_________________ in which the axis points continually _________________.
42. What effect on the seasons does precession have?
43. What does precession cause?
44. How else is Earth moving?
45. How many natural satellites does Earth have? What is its name?
46. What direction is the moon orbiting the Earth?
47. Compare the moon at its perigee and its apogee.
48. What are the phases of the moon?
49. Compare the moon at waxing and waning.
50. Compare the moon at full-moon phase and new-moon phase.
51. _________________ phases are a result of the _________________ of the moon and the
_________________ that is reflected from its surface.
52. The cycle of the _________________ through its phases requires _________________ days, a time span
called the _________________ month. This cycle was the basis for the first Roman _________________.
53. How long is the sidereal month?
54. An interesting fact about the motions of the _________________ is that the moon’s period of
_________________ about its _________________ and its _________________ around Earth are the
_________________. Because of this, the _________________ side of the moon _________________
faces Earth.
55. What are eclipses?
56. What produces a solar eclipse?
57. What produces a lunar eclipse?
58. During a new-moon or full-moon phase, the moon’s _________________ must cross the plane of the
_________________ for an _________________ to take place.
Section 3 – Earth’s Moon
59. Why is our planet-satellite system unusual in the solar system?
60. Where did we get much of what we know about the moon?
61. What is the gravitational attraction difference between the Earth and the moon?
62. What are the most obvious feature of the lunar surface?
63. What are craters?
64. How were most craters produced?
65. What are highlands?
66. What is found in the highland regions?
67. What are maria?
68. Maria, _________________ beds of basaltic lava, originated when _________________ punctured the
lunar surface, letting _________________ bleed out.
69. What is lunar regolith?
70. What is lunar regolith composed of?
71. The most widely accepted model for the _________________ of the _________________ is that when the
_________________ system was forming, a body the size of _________________ impacted Earth.
72. What is the name of this impact?
73. Name the three phases of moons history.