Astro Unit 3

In the Greek geocentric model, the retrograde motion of a planet occurs when

• the planet actually goes backward in its orbit around Earth.

• the planet is aligned with the Moon in our sky.

• Earth is about to pass the planet in its orbit around the Sun.

When we say that a planet has a highly eccentric orbit, we mean that

• its orbit is an ellipse with the Sun at one focus.

• it is spiraling in toward the Sun.

• in some parts of its orbit it is much closer to the Sun than in other parts.

Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law

• Earth travels faster in its orbit around the Sun in July than in January.

• Earth travels faster in its orbit around the Sun in January than in July.

• it is summer in January and winter in July.

Which of the following statements best describes the accomplishments of these three people?

• Tycho collected the data, Kepler provided the model in the form of laws, Newton explained the model in terms of gravity.

• Tycho collected the data, Kepler provided the model in the form of laws, Newton explained the model in terms of gravity.

• Kepler collected the data, Tycho provided the model in the form of laws, Newton explained the model in terms of gravity.

• Tycho collected the data, Newton provided the model in the form of laws, Kepler explained the model in terms of gravity.

Galileo challenged the idea that objects in the heavens were perfect by

• showing that heavy objects fall at the same rate as lighter objects.

• observing sunspots on the Sun and mountains on the Moon.

• proving Kepler's laws were correct.

• inventing the telescope.

Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun?

• phases of Venus

• four moons of Jupiter

• patterns of shadow and sunlight near the dividing line between the light and dark portions of the Moon's face

• The Milky Way is composed of many individual stars

Which person below did the following? He tried fitting perfect circles to Tycho's data, but in doing so found discrepancies of up to 8 arc minutes. Because he was confident that Tycho's data had uncertainties of only 1 arc minute, he abandoned perfect circles, which led him to a model using elliptical orbits.

• Galileo

• Newton

• Copernicus

• Kepler

When Copernicus first created his Sun-centered model of the universe, it did not lead to substantially better predictions of planetary positions than the Ptolemaic model. Why not?

• Copernicus used perfect circles for the orbits of the planets.

• Copernicus placed the planets in the wrong order going outward from the Sun.

• Copernicus misjudged the distances between the planets.

• Copernicus placed the Sun at the center but did not realize that the Moon orbits the Earth.

How does a 12-month lunar calendar differ from our 12-month solar calendar?

• It has about 11 fewer days.

• It does not have seasons.

• Its new year always occurs in February instead of on January 1.

• It uses a 23-hour rather than a 24-hour day.

Suppose the planet Uranus were much brighter in the sky, so that it was as easily visible to the naked eye as Jupiter or Saturn. Which one of the following statements would most likely be true in that case?

• The discovery that the Earth is a planet going around the Sun would have come hundreds of years earlier.

• Its gravity would cause the tides to be much higher than they actually are.

• Its brightness would make it possible to read by starlight at night.

• A week would have 8 days instead of 7.