Download Astro 1050 HW #2

Astro 1050 HW #2
1. Describe the difference between the Ptolemaic and the Copernican systems in explaining
retrograde motion.
2. If Copernicus’s heliocentric model did not give significantly more accurate predictions
than Ptolemy’s geocentric model, why do we now prefer Copernicus’s model?
3. The Earth is closer to the Sun in January each year. Use Kepler’s second law to describe
the Earth’s relative speeds in January and July.
4. If a hypothetical planet is 4 times farther from the Sun than Earth is, what is its orbital
speed relative to Earth’s? Hint: Remember v= 2a/P for (near-)circular orbits
5. What is the period of a planet orbiting 3 AU from a star that is 3 times as massive as the
Sun? Hint: use Newton’s version of Kepler’s 3rd law and ratios!!! Remember mass is not
constant here
6. T/F: Although the values of the constants may differ, Newton showed that Kepler’s laws
apply equally well to the moons orbiting Jupiter as they do Jupiter orbiting the Sun.
7. Two planets orbit a star that has the same mass as the Sun. Planet A orbits at a distance
of 2 AU while Planet B orbits at 1 AU. What is Planet A’s orbital period compared to
Planet B’s?
8. The retrograde motion of Venus across the sky
a. Is caused by the “backward” rotation of Venus about its own axis
b. Is caused by the gravitational tug of other planets on Venus
c. Is caused by the change in perspective as Venus catches up with and passes Earth
d. Is caused by the motion of Venus along an epicycle whose center orbits the Sun
e. Was used by Galileo to explain the complete set of phases of Venus that he
observed through his telescope
9. Although Kepler developed three laws of planetary motion, ___________ developed a
physical understanding of these laws.
10. In the model of the Universe developed by Aristotle, the outermost sphere was that of the
__________.
11. Why are we more likely to learn about the early history of the Earth by studying the rocks
from the moon than those on Earth?
12. Why do we think that there have been significant external effects on the rotation of
Venus?
13. T/F: Earth’s moon has a composition similar but not identical to that of Earth’s crust,
consistent with the hypothesis that the Moon formed after a large objected collided with
Earth.
14. T/F: At any given coastal location on Earth, high tide occurs only once per day, when the
Moon is overhead.
15. T/F: The terrestrial planets have iron cores and rocky outer parts; the iron sank when
they were young and molten.
16. Which of the following statements about the Earth-Moon system is true?
a. The same half of the Moon’s surface is perpetually dark
b. At a given location on Earth, there are two high tides each day – one caused by
the gravitational pull from the Sun and the other by the gravitational pull from the
Moon
c. High tide occurs on the side of the Earth nearest to the moon, while low tide
occurs on the opposite side of the Earth
d. By observing the Moon long enough from Earth, night after night, we are able to
draw a map of its entire surface
e. The orbital period of the Moon around the Earth and the rotation period of the
Moon around its axis are equal
17. Earth’s ________ occur in regions where Earth’s magnetic field lines intersect its
atmosphere, as a result of collisions between charged particles in air molecules.
18. A planet is said to be in ________ when it moves in front of a star (along our line-ofsight).
19. Compare the rings of Jupiter, Saturn, Uranus, and Neptune.
20. The low average densities of Jupiter and Saturn compared with Earth suggest that:
a. They are hollow
b. Their gravitational attraction has squeezed material out of their cores
c. They consists mostly of water
d. They contain large quantities of light elements, such as hydrogen and helium
e. Volcanic eruptions have ejected all the iron that was originally in their cores
21. What is the main reason Pluto is now considered a dwarf planet rather than a genuine
planet?
22. Use Kepler’s third law and the known period of Halley’s Comet (76 years) to calculate its
semi-major axis. Which planet has a comparable semi-major axis? Hint: use ratios and
be away of your units
23. T/F: Comets are made of mostly rocky material from the asteroid belt.
24. Discuss similarities and differences in the way terrestrial planets and giant planets formed
in our Solar System.
25. Many of the giant exoplanets are quite close to their parent stars. If they initially formed
farther out, how could they have ended up and their observed positions?
26. What was the special importance of the discovery of a system of several planets (rather
than just one) orbiting a star?
27. The giant planets are large compared to the terrestrial planets because the giant planets:
a. Have higher densities
b. Formed by the same process as the Sun and can be considered miniature stars
c. Have many moons
d. Obtained and retained more gas and ice because of their large distance from the
Sun
e. Did not suffer as many major, destructive collisions as the terrestrial planets