astronomy ch 3
1. Practical value of ancient astronomy:
Timekeeping, tracking seasons, creating calendars, and navigation.
2. How central Africans predicted rainfall:
By observing the tilt and orientation of the waxing crescent moon.
3. Months with fewer than 100 mm of rainfall:
Jan., Feb., Mar., Sept., Oct., Nov., and Dec.
4. Names of the seven days of the week:
The seven celestial bodies visible to the naked eye that move across the sky: Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn.
5. Reason for attention to ancient Greek science:
They were the first to explain nature using models based on math and logic rather than myth.
6. How Eratosthenes estimated Earth's size:
By comparing the angles of shadows cast by sunlight at noon in two different cities on the summer solstice.
7. Description of the geocentric universe:
A model where Earth sits motionless at the center of the universe while everything else orbits around it.
8. Reason Greeks rejected Earth's movement:
They could not detect stellar parallax (the apparent shift of stars caused by Earth moving).
9. Ptolemy’s contribution:
He built a complete geocentric model using epicycles that predicted planetary positions for centuries.
10. Location of the Sun in Ptolemy’s model:
Orbiting Earth, placed between the orbits of Venus and Mars.
11. Reason for "circles upon circles" (epicycles):
To explain retrograde (backward) motion while keeping circular orbits centered on Earth.
12. Scholars who preserved Greek work during the Dark Ages:
Islamic scholars.
13. Copernicus’s main contribution:
He introduced a mathematical heliocentric (Sun-centered) model.
14. Flaw in Copernicus’s model: He assumed orbits were perfect circles, making his model no more accurate than Ptolemy's.
15. Tycho Brahe’s contribution: Extremely detailed and accurate naked-eye observations of planetary positions.
16. Astronomer who angered the Pope:
Galileo Galilei.
17. 5 discoveries Galileo made with his telescope:
1. Four moons orbiting Jupiter
2. Phases of Venus
3. Sunspots on the Sun
4. Mountains and craters on the Moon
5. The Milky Way is made of vast numbers of individual stars
18. Galileo's discoveries about the Sun and Moon:
The Moon has a rough surface with craters, and the Sun has dark, moving spots.
19. Kepler’s Three Laws of Planetary Motion:
1. Orbits are ellipses with the Sun at one focus.
2. A planet sweeps out equal areas in equal times (moves faster when closer to the Sun).
3. p² = a³ (More distant planets take longer to orbit the Sun).
20. Error in the planetary orbit picture:
The Sun is drawn in the middle of the orbit instead of at one focus.
21. Point where planet travels fastest:
Point 1 (closest to the Sun).
22. Northern Hemisphere season when Earth moves fastest:
Winter (in January, when Earth is closest to the Sun).
23. Terms in p² = a³: p = Orbital period in years; a = Average distance from the Sun in astronomical units
24. Comet orbital calculation at 4 AU: 8 years (p² = 4³ = 64, so p = 8)
25. Perihelion:
The point in an orbit closest to the Sun.
26. Aphelion:
The point in an orbit farthest from the Sun.
27. Purpose of scientific models:
To explain and predict real-world observations.
28. Truth about scientific models:
They must make testable predictions and be changed or discarded if observations disprove them.
29. Scientific definition of a theory:
A well-tested, powerful explanation supported by extensive evidence that has survived repeated testing.
30. Ancient goal of astrology:
To predict human events and fortunes using the positions of celestial objects.