### Chapter 3

1. Precession is the slow motion of the Earth's rotation axis on the celestial sphere
the apparent backward motion of the stars from night to night
the accuracy of an astronomical measurement in arcseconds
the motion of the sun relative to that of the Earth
the motion of the planets during retrograde motion
2. Something which is 100 km away has an angular size of 2 seconds of arc.
Approximately how tall is it? 1 m
10 m
100 m
1 km
3. An object with an angular size of 1 degree moves three times farther away. What is its new angular size? 3 degrees
20 minutes of arc
3 minutes of arc
33 seconds of arc
4. Which of the following is a reason that the ancient Greek astronomers rejected Aristarchus' heliocentric model of the solar system? it did not account for retrograde motions of the planets
it could not explain the phases of Venus
they could detect no stellar parallax
it could not account for the Coriolis effect
5. What quantity did Aristarchus have to estimate in order to find the relative distances of the sun and the moon? the angular sizes of the sun and moon
the angle between the sun and moon at the time of quarter moon
the parallax of the moon
the length of time between successive solar and lunar eclipses
6. How did Eratosthenes determine the size of the Earth? by observing the lengths of shadows at different locations
by observing the size of the Earth's shadow during eclipses
by determining the density and mass of the Earth
by measuring the parallax of the moon
7. What evidence did Aristotle offer for his argument that the Earth is a sphere? he had travelled around it
the other planets are spheres
the shadow of the Earth during a lunar eclipse is curved
the Sun set in the west and then rose in the east the next morning
8. An astronaut lands on an unknown planet. After walking a distance of 200 km toward the north pole of the planet, she notices that the pole star for that planet is 5 degrees higher in the sky. What is the circumference of the planet? 14,400 km
1000 km
20,600 km
3,600 km
9. Why were epicycles used in Ptolemy's model of the solar system? to account for the parallaxes of stars
to compensate for the ellipticity of the orbits of the planets
to explain the retrograde motions of planets
to explain the phenomenon of day and night
10. What role did the equant play in Ptolemy's model of the solar system? it hid the Sun from view at night