Astronomy - Chapter 3

Aphelion

point in a planet's orbit that is farthest from the sun

Kelper's second law

states that an imaginary line from the sun to a planet sweeps out equal areas in equal time intervals

The shadow cast by a simple stick or obelisk allowed ancient people to

tell the time of day

On (Figure 1), you can see Kepler's third law (p2=a3p2=a3) from the fact that __________.

the data fall on a straight line

Kepler's third law is often stated as p2=a3p2=a3. The value a3a3 for a planet is shown on __________.

the horizontal axis of Figure 1

An original observation of Galileo's that helped to overturn the ancient Earth-centered model was

the phases of Venus

Galileo's contribution to astronomy included:

making observations and conducting experiments that dispelled scientific objections to the Sun-centered model.

eccentric

measure of how stretched out an ellipse is; a perfect circle has no ______. The most stretched out ellipse has the largest _____.

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

more than 56 days.

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

never

Kelper's Third Law

p^2=a^3, where p is the planet's orbital period in years and a is the average orbital distance in AU

Consider the hypothetical observation "a planet beyond Saturn rises in west, sets in east." This observation is not consistent with a Sun-centered model, because in this model __________.

the rise and set of all objects depends only on Earth's rotation

Uranus, not shown on the graph, orbits about 19 AUAU from the Sun. Based on the graph, its approximate orbital speed is between about __________.

5 and 10 km/s

According to Kepler's third law:

Jupiter orbits the Sun at a faster speed than Saturn.

You discover an asteroid that orbits the Sun with the same 1-year orbital period as Earth. Which of the following statements must be true?

The asteroid's average (semimajor axis) distance from the Sun is 1AU

"A huge fleet of alien spacecraft will land on Earth and introduce an era of peace and prosperity on January 1, 2035."

The claim can be evaluated scientifically by seeing whether or not the aliens show up on the appointed date.

As a comet orbits around the Sun, its maximum speed is twice its minimum speed. What can we say about its orbit?

The comet is twice as far from the Sun at aphelion as at perihelion

Kelper's First Law

The orbits were elliptical (egg-shaped) was known as ____. -must be an ellipse with the Sun at one focus. Therefore, the path that shows the Sun in the center of the ellipse, rather than at a focus, cannot be the real orbital path of a planet

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

The planet actually goes backward in its orbit around Earth.

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

When would a new Venus be highest in the sky?

at noon

Suppose (Figure 1) showed a planet on the red line directly above a value of 1000 AU3AU3 along the horizontal axis. On the vertical axis, this planet would be at

1000years^2

How far does the planet in part F orbit from the Sun?

10AU

Jupiter orbits the Sun at an average distance of 5.2035.203 AU and takes11.86 years to complete each orbit. Based on these facts, which statement is true?

11.862=5.2033

All of the following statements are true. Which one can be explained by Kepler's third law?

Venus orbits the Sun at a faster orbital speed than Earth.

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.

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

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

When Einstein's theory of gravity (general relativity) gained acceptance, it demonstrated that Newton's theory had been

incomplete

We never see a crescent Jupiter from Earth because Jupiter __________.

is farther than Earth from the Sun

Why wasn't the Sun-centered model of Copernicus immediately adopted after he proposed it?

it was not noticeably more accurate than the old Ptolemaic model

A planet is discovered orbiting the star 51 Peg with a period of four days (0.01 years). 51 Peg has the same mass as the Sun. Mercury's orbital period is 0.24 years, and Venus's is 0.62 years. The average orbital radius of this planet is

less than Mercury's

Kepler's third law states that a planet's orbital period, p, is related to its average (semimajor axis) orbital distance, a, according to the mathematical relationship p2=a3p2=a3. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's third law?

-Inner planets orbit the Sun at higher speed than outer planets. -Venus orbits the Sun faster than Earth orbits the Sun.

Which of the following are the three key hallmarks of science?

-Science progresses through the creation and testing of models of nature that explain the observations as simply as possible.--Modern science seeks explanations for observed phenomena that rely solely on natural causes.---Models must make testable predictions that will force us to revise or abandon the model if they do not agree with observations.

Which of the following statements describe a characteristic of the solar system that is explained by Kepler's first law?

-The Sun is located slightly off-center from the middle of each planet's orbit. -Earth is slightly closer to the Sun on one side of its orbit than on the other side.

Which of the following is not true about a scientific theory?

A theory is essentially an educated guess.

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 January than in July.

Why do the planets orbit the Sun (i.e. why don't they crash into the Sun)?

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.

Earth is slightly closer to the Sun in January than in July. How does the area swept out by Earth's orbit around the Sun during the 31 days of January compare to the area swept out during the 31 days of July?

Both areas are the same.

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.

How does its average distance compare to that of Pluto

Eris orbits farther than Pluto

If an astronomer claims to have discovered an object with a very eccentric orbit, which of the following best describes the orbital trajectory of the object?

It looks like a very squashed oval.

Which of the following was not a major advantage of Copernicus's Sun-centered model over the Ptolemaic model?

It made significantly better predictions of planetary positions in our sky.

Kepler's second law states that as a planet orbits the Sun, it sweeps out equal areas in equal times. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's second law?

Pluto moves faster when it is closer to the Sun than when it is farther from the Sun.

All of the following statements are true. Which one can be explained by Kepler's second law?

Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun.

Ptolemaic System

Model of the universe with Earth at the center

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 is not true about scientific progress?

Science advances only through the scientific method.

What is its average distance (semimajor axis) from the Sun?Express your answer using three significant figures.

a = 67.7 AU

Approximately how fast is Jupiter orbiting the Sun?

a little less than 15 km/s

An asteroid with an average orbital distance of 2 AUAU will orbit the Sun at an average speed that is __________.

a little slower than the orbital speed of Mars

Tycho Brahe's contribution to astronomy included:

collecting data that enabled Kepler to discover the laws of planetary motion.

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

semimajor axis

half of the longest diameter across an ellipse

If Earth's orbit were very eccentric, but the average distance from the Sun were still 1 AU, its orbital period

would still be one year.