Astronomy 3 Chapter 3

In the Greek geocentric model, the retrograde motion of a planet occurs when: A. Earth is about to pass the planet in its orbit around the Sun. B. The planet actually goes backward in its orbit around Earth. C. The planet is aligned with the Moon in our sky.

The planet actually goes backward in its orbit around Earth

If Earth's orbit were very eccentric, but the average distance from the Sun were still 1 AU, its orbital period: A. would still be one year. B. would be longer than one year. C. would be less than one year

Would be still one year

According to Kepler's law: A. Mercury travels fastest in the part of its orbit in which it is closest to the Sun. B. Jupiter orbits the Sun at a faster speed than Saturn. C. All the planets have nearly circular orbits.

B. Jupiter orbits the Sun at a faster speed than Saturn.

Two planets are observed going around a star. Planet Xoron has an orbital period that is twice as long as planet Krypton. Which planet has a shorter average orbital radius?

Planet Krypton

Which of the following can you observe about Venus with the naked eye? Select all that apply. A. Venus sometimes shines brightly in the western sky shortly after sunset B. Venus is visible at midnight when it is in its full phase C. Venus sometimes shines brightly in the eastern sky shortly before dawn D. When Venus is brightest, it is visible all night long

A. Venus sometimes shines brightly in the western sky shortly after sunset; C. Venus sometimes shines brightly in the eastern sky shortly before dawn

Why do the planets orbit the Sun(i.e. why don't they crash into the Sun)? A. There is no gravity in space. B. Although the planets experience a force of gravity from the Sun, since they are moving, their trajectories bend around the Sun rather than lead directly into the Sun. C. All astronomical objects move in circular orbits.

Although the planets experience a force of gravity from the Sun, since they are moving, their trajectories bend around the Sun rather than lead directly into the Sun

If an astronomer claims to have discovered an object with a very eccentric orbit, the orbital trajectory of the object: A.It is circular. B. It looks like a figure 8. C. It looks like a very squashed oval. D. None of the above.

C. It looks like a very squashed oval

When we say that a planet has a highly eccentric orbit, we mean that: A. it is spiraling in toward the Sun. B. its orbit is an ellipse with the Sun at one focus. C. in some parts of its orbit it is much closer to the Sun than in other parts.

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

Suppose two comets, comet A and comet B, were orbiting the Sun, having the same average orbital radii. If comet A had a higher eccentricity than comet B, which comet would, during some portion of its orbit, have the highest orbital speed?

Comet A

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

Earth travels fast in its orbit around the Sun in January than in July

The Moon takes roughly 28 days to complete one orbit around Earth. If the orbital radius of the Moon were twice its actual value, its orbital period would be: A.less than 28 days. B.roughly 28 days. C.roughly 56 days. D.more than 56 days.

more than 56 days