Chapter 2 Questions

Vocab

1. Earth is located at one focus of the Moon's orbit. 2. According to Kepler's second law, Jupiter will be traveling most slowly around the Sun when at aphelion. 3. Earth orbits in the shape of a/an ellipse around the Sun. 4. The mathematical form of Kepler's third law measures the period in years and the semimajor axis in astronomical units (AU). 5. According to Kepler's second law, Pluto will be traveling fastest around the Sun when at perihelion. 6. The extent to which Mars' orbit differs from a perfect circle is called its eccentricity

An accurate sketch of Jupiter's orbit around the Sun would show

A nearly perfect circle

why the geocentric model was accepted for so long.

There was parallax as the Earth moved around the Sun, but it was not measurable until the mid-1800s. There was no sensation of motion as the Earth moved through space

What does it mean to say that Kepler's laws are empirical?

They resulted solely from the analysis of observational data and we're not derived from any theory of mathematical model

A calculation of how long it takes a planet to orbit the sun would be most closely related to Kelplers

Third law of planetary distances

Which of the following is the best summary of Galileo's observations of the phases of Venus that directly refuted the Ptolemaic (geocentric) model?

Venus can be seen to exhibit a full phase, which is predicted not to happen in the geocentric model.

Newton's law of gravity states that the force between two objects

d) increases with mass.

Which of Galileo's initial observations was most challenging to established geocentric beliefs?

d) satellites of Jupiter.

The heliocentric model assumes

d) the Sun is the center of the solar system.

What is a scientific theory?

well-tested explanation that unifies a broad range of observations and makes predictions about real world

In Ptolemy's Earth-centered model for the solar system, Venus's phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.

full whenever it is on the opposite side of the Sun from Earth, although we cannot see the full Venus because it is close to the Sun in the sky A full Venus always occurs when it is on the opposite side of the Sun as viewed from Earth. (However, we cannot see the full Venus, because it is always very close to the Sun in the sky at that time.) Galileo used this fact as evidence for the Sun-centered view of the solar system: The fact that Venus goes through all the phases must mean it goes all the way around the Sun. In contrast, in the Ptolemaic model, Venus only varies between new and crescent phases.

What is the great contribution of Copernicus to our knowledge of the solar system? What was still a flaw in the Copernican model?

The great contribution of Copernicus was that the solar system is heliocentric and not geocentric, but Copernicus believed that the planets moved in perfect circular motion around the sun

If the Sun and its mass were suddenly to disappear, Earth would

fly off into space

What contributions to astronomy were made by Chinese and Islamic astronomers during the Dark Ages?

Chinese often documented major events in the sky like Supernovas in 1054 AD Islamic culture helped maintained a link b/w old Greek astronomy, deve triangulation, star names like Vega

Circle of Scientific Progress

Copernicus made a radical conceptual leap away from the Ptolemaic view, gaining insights but little in predictive power. Kepler made changes to Copernican picture and gained accuracy and predictive power, but fell short of true physical explanation of planetary motions or orbital motions. Eventually Newton showed how all known planetary motion can be explained by the 3 laws of motion and law of gravity.

What would happen to the orbits of each of the planets if the force of gravity was suddenly "turned off"?

Each would move off in a different straight line

How do Newton's laws account for Kepler's Laws.

Kepler's Laws are a consequence of Newtons bc it describes the laws of motion and gravity.

During the Dark Ages (roughly from the 5th to the 10th century A.D.), turmoil in Europe largely halted the progress of Western science. Which culture provided the vital link between the astronomy of ancient Greece and that of medieval Europe during this time?

Muslim

In the geocentric Greek model, which of the following objects did not require an epicycle?

Sun

What discoveries of Galileo helped confirm the views of Copernicus and how did they do so?

The discoveries of Jupiter's moons and the Phases of Venus confirmed Copernicus's views. The fact that another planet had moons provided the strongest support for the Copernican model. The Phases of Venus could only be explained only by the planet's motion around the sun

In what sense is the Moon falling toward Earth? How can we use to measure the Earth's mass?

The earth has a gravitational inward pull on the moon. Can find the mass of an object by measuring its gravitational influence on another object

The benefit of our current knowledge lets us see flaws in the Ptolemaic model of the universe. What is its basic flaw?

The earth is not the center and orbits are ellipsis

Earth is closer to the Sun in January. From this fact, Kepler's second law tells us

b)Earth orbits faster in January.

In Ptolemy's Earth-centered model for the solar system, Venus always stays close to the Sun in the sky and, because it always stays between Earth and the Sun, its phases range only between new and crescent. The following statements are all true and were all observed by Galileo. Which one provides evidence that Venus orbits the Sun and not Earth?

We sometimes see gibbous (nearly but not quite full) Venus.

Was it possible for the geocentric system of Ptolemy to explain the observed retrograde motion of the planets?

Yes, through a system of epicycles and deferents Was still able to predict the retrograde motion of the planets well enough

Which hero of the Renaissance postulated three "laws" of planetary motion?

a) Kepler.

Kepler's first law of planetary motion states that

a) planets orbit the Sun. b) orbits are noncircular. c) orbits are elliptical in shape. d) all of the above are correct d

The geocentric model was supported by Aristotle because

a) stars don't seem to show any parallax. b) we don't feel as though Earth moves. c) objects fall toward Earth, not the Sun. d) we don't see an enormous wind. e) all of the above were valid reasons e

Newton explained Kepler's First Law by saying that a planet and the Sun have an ------ for each other and they do not crash into each other because they have been moving from the beginning.

an attraction

Kepler's Second Law can be explained as follows: as a planet approaches the Sun from----- to -------, it is moving ------------ of the force of gravity (toward the Sun) and thus it ------.

aphelion perihelion in the direction of speeds up

When would a new Venus be highest in the sky?

at noon

Imagine that Venus is in its full phase today. If we could see it, at what time would the full Venus be highest in the sky?

at noon Because Venus is full when it is on the opposite side of the Sun from Earth, the Sun and Venus both appear to move through the sky together at that time. Venus therefore rises with the Sun, reaches its highest point at noon, and sets with the Sun.

Who published the first astronomical observations made with a telescope?

b) Galileo

Kepler's third law relates a planet's distance from the Sun and its orbital

b.)period.

Mars, Jupiter, and Saturn show retrograde motion because

c) Earth moves faster in its orbit.

Copernicus' important contribution to astronomy was

c) proposing a simpler model for the motions of planets in the solar system.

Epicycles were used in Ptolemy's model to explain

c) why retrograde motion occurred.

Showing the motion of a ball near Earth's surface, depicts how gravity

causes the ball to accelerate downward

A major flaw in Copernicus's model was that it still had

circular orbits

Kepler's Third Law can be explained as follows: ------------- the Sun is an important factor determining the strength of the gravitational force between a planet and the Sun, which in turn controls orbital speed.

distance of a planet from

Copernicus' heliocentric model was flawed because

e) he assumed planets moved in circles.

How did the geocentric model account for day and night on Earth?

e) the Sun orbited Earth.

Retrograde motion was explained by the Greeks by inventing which of the following?

epicycles Epicycles (multiple spheres) were a clever way to explain the apparent backwards motion of the planets while still maintaining the ideal of uniform circular motion.

An asteroid with an orbit lying entirely inside Earth's

has an orbital semimajor axis of less that 1 AU

If Earth's orbit around the Sun were twice as large as it is now, the orbit would take

more than two times longer to traverse

The orbits of 2 stars of unequal masses. If one star has twice the mass of the other, then the more massice star

moves more slowly

When would you expect to see Venus high in the sky at midnight?

never

Galileos observations of Venus demonstrated that Venus must be

orbiting the sun

From ------- to ------, the planet is moving away from the Sun, ------------- the gravitational force, and the planet---------.

perhelion aphelion in the opposite direction slows down

Planets near opposition

rise in the east