Astronomy Practice Questions & Homework - Chapter 03

What is Earth-centered only?

a planet beyond Saturn rises in west, sets in east.

According to Kepler's second law, Jupiter will be traveling most slowly around the Sun when at _____.

aphelion

The extent to which Mars' orbit differs from a perfect circle is called its _____.

eccentricity

Earth is located at one _____ of the Moon's orbit.

focus

What are 2 falsifiable (could be proven false) statements?

(1.) Kennedy died from a bullet in his brain. (2.) Kennedy was the 35th president of the United States. Correct. Note that both of the falsifiable claims in this example happen to be true. The claim about Kennedy being the 35th President is falsifiable because it can be checked against historical records. The claim that Kennedy died from a bullet in his brain is falsifiable because it could have been shown false by the medical examiner. The remaining claims are not falsifiable: Statements that call on any type of supernatural being are by definition out of the realm of science. Similarly, a claim of something being "undetectable" could not be falsified, and a claim about what Kennedy would have done if he had lived is a conjecture that cannot be disproven.

Process of Science Task: Earth-Centered vs. Sun-Centered Models. Learning Goal: To understand how evidence allows us to distinguish between alternate possible models of the solar system. Imagine that you did not know whether Earth is the center of the solar system (as the Greeks assumed) or just one planet going around the Sun. In this activity, you will consider a set of observations, some real and some not real, that could help you distinguish between the Greek Earth-centered model and our modern Sun-centered model. Note that, in the Greek Earth-centered model, the planets Mercury and Venus lie between Earth and the Sun, while all other planets orbit Earth beyond the orbit of the Sun. Consider the following observations. Classify each observation based on whether it is a real observation (a true statement of something we can actually see from Earth) or one that is not real (a statement of something that does not really occur as seen from Earth).

(1.) Mercury goes through a full cycle of phases. (2.) Moon rises in east, sets in west. (3.) stars circle daily around north or south celestial pole. (4.) positions of nearby stars shift slightly back & forth each year. (5.) a distant galaxy rises in east, sets in west each day. (6.) a planet beyond Saturn rises in west, sets in east. (7.) we sometimes see a crescent Jupiter.

Consider again the set of observations from Part A. This time, classify each observation according to whether it is consistent with only the Earth-centered model, only the Sun-centered model, both models, or neither model. (Note that an observation is "consistent" with a model if that model offers a simple explanation for the observation.)

(1.) Mercury goes through a full cycle of phases. (2.) Moon rises in east, sets in west. (3.) stars circle daily around north or south celestial pole. (4.) positions of nearby stars shift slightly back & forth each year. (5.) a distant galaxy rises in east, sets in west each day. (6.) a planet beyond Saturn rises in west, sets in east. (7.) we sometimes see a crescent Jupiter. Correct. Now continue to the follow-up questions to check that you understand why the observations fall into these categories.

What are 5 real (true) statements?

(1.) Mercury goes through a full cycle of phases. (2.) Moon rises in east, sets in west. (3.) stars circle daily around north or south celestial pole. (4.) positions of nearby stars shift slightly back & forth each year. (5.) a distant galaxy rises in east, sets in west each day. Correct. Before you continue to Part B, think about why each of the preceding observations are real or not real.

What is both models?

(1.) Moon rises in east, sets in west. (2.) a distant galaxy rises in east, sets in west each day. (3.) stars circle daily around north or south celestial pole.

What are 4 (could be proven false) falsifiable statements?

(1.) The Sun is at the center of the solar system. (2.) The chemical content of the universe is mostly hydrogen and helium. (3.) The observable universe contains approximately 100 billion galaxies. (4.) Earth is at the center of the solar system.

What are 3 not (could not be proven false) falsifiable statements?

(1.) The laws of nature are magnificent and beautiful. (2.) The universe was created by God. (3.) We are all playthings in a computer program created by advanced aliens.

What are 4 not falsifiable (could not be proven false) statements?

(1.) The murder of John F. Kennedy was an act of evil. (2.) Kennedy's death was the will of God. (3.) Kennedy's murder was orchestrated by an undetectable shadow government of the United States. (4.) If he'd lived, Kennedy would have ended the Vietnam War.

What are 2 not real (false) statements?

(1.) a planet beyond Saturn rises in west, sets in east. (2.) we sometimes see a crescent Jupiter.

What is sun-centered only?

(1.) positions of nearby stars shift slightly back & forth each year. (2.) Mercury goes through a full cycle of phases.

When would a new Venus be highest in the sky? A. at noon. B. just after sunset. C. just before dawn. D. midnight.

A. at noon. Correct. A new Venus occurs when Venus is directly between the Sun and Earth, which means a new Venus will be highest in the sky at the same time that the Sun is highest in the sky, which is around noon (local time).

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 __________. A. the rise and set of all objects depends only on Earth's rotation. B. all objects in space must orbit the Sun in the same direction. C. planets beyond Saturn must orbit the Sun more slowly than closer-in planets. D. there are no planets beyond Saturn.

A. the rise and set of all objects depends only on Earth's rotation. Correct. Earth rotates from west to east, so objects in the sky must appear to go across our sky from east to west.

Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law: A. Earth travels faster in its orbit around the Sun in July than in January. B. Earth travels faster in its orbit around the Sun in January than in July. C. It is summer in January and winter in July

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

Which of the following was not a major advantage of Copernicus's Sun-centered model over the Ptolemaic model? A. It allowed calculation of the orbital periods and distances of the planets. B. It made significantly better predictions of planetary positions in our sky. C. It offered a more natural explanation for the apparent retrograde motion of planets in our sky.

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

According to Kepler's third 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.

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.

B. The planet actually goes backward in its orbit around 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? A. We never see Venus at midnight. B. We sometimes see gibbous (nearly but not quite full) Venus. C. We sometimes see a crescent Venus. D. We need a telescope to observe the phases of Venus.

B. We sometimes see gibbous (nearly but not quite full) Venus. Correct. In the Ptolemaic system, we should never see more than a crescent in Venus. Because we do in fact see more, the Ptolemaic model must be wrong. The full range of phases that we see for Venus is consistent only with the idea that Venus orbits the Sun. Galileo was the first to observe the phases of Venus — and hence to find this evidence in support of the Sun-centered system — because he was the first to observe Venus through a telescope. Without a telescope, we cannot tell that Venus goes through phases.

We never see a crescent Jupiter from Earth because Jupiter __________. A. shines with its own light. B. is farther than Earth from the Sun. C. does not go around Earth. D. orbits the Sun in the same direction as Earth.

B. is farther than Earth from the Sun. Correct. An object must come between Earth and the Sun for us to see it in a crescent phase, which is why we see crescents only for Mercury, Venus, and the Moon.

Which of the following is not true about a scientific theory? A. A theory must explain a wide range of observations or experiments. B. Even the strongest theories can never be proved true beyond all doubt. C. A theory is essentially an educated guess.

C. A theory is essentially an educated guess.

Tycho Brahe's contribution to astronomy included: A. inventing the telescope. B. proving that Earth orbits the Sun. C. collecting data that enabled Kepler to discover the laws of planetary motion.

C. 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 __________. A. never full because the sunlit side of Venus never faces directly toward Earth B. never full because Earth's shadow falls on Venus at the time when it would otherwise be full C. 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 D. full whenever it lies directly between Earth and the Sun

C. 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. Correct. 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.

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.

Galileo's contribution to astronomy included: A. discovering the laws of planetary motion. B. discovering the law of gravity. C. making observations and conducting experiments that dispelled scientific objections to the Sun-centered model.

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

Let's now consider possible scientific claims. Recall that a scientific claim is falsifiable if it could in principle be shown to be false by observations or experiments, even if those observations or experiments have not yet been performed. Classify each claim according to whether or not it is falsifiable.

Categorize it as falsifiable and not falsifiable.

Part D Each of the following diagrams shows a planet orbiting a star. Each diagram is labeled with the planet's mass (in Earth masses) and its average orbital distance (in AU). Assume that all four stars are identical. Use Kepler's third law to rank the planets from left to right based on their orbital periods, from longest to shortest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality. (Distances are to scale, but planet and star sizes are not.)

Correct Kepler's third law tells us that the orbital period of the planet depends on its average distance from its star, but not on the planet's mass. As Newton later showed with his version of Kepler's third law, this is actually an approximation that works well whenver the planet's mass is small compared to the mass of the star.

Part B The following diagrams are the same as those from Part A. This time, rank the planets from left to right based on the amount of time it takes each to complete one orbit, from longest to shortest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality. (Distances are to scale, but planet and star sizes are not.)

Correct Recall that the time it takes a planet to complete an orbit is called its orbital period. The pattern found in this Part illutrates one of the ideas that are part of Kepler's third law: Planets with larger average orbital distances have longer orbital periods.

Part C The following diagrams are the same as those from Parts A and B. This time, rank the planets from left to right based on their average orbital speed, from fastest to slowest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality. (Distances are to scale, but planet and star sizes are not.)

Correct This pattern illustrates another of the ideas that are part of Kepler's third law: Planets with larger average orbital distances have slower average speeds.

Ranking Task: Kepler's Third Law of Planetary Motion Part A The following diagrams all show the same star, but each shows a different planet orbiting the star. The diagrams are all scaled the same. (For example, you can think of the tick marks along the line that passes through the Sun and connects the nearest and farthest points in the orbit as representing distance in astronomical units (AU).) Rank the planets from left to right based on their average orbital distance from the star, from longest to shortest. (Distances are to scale, but planet and star sizes are not.)

Correct. Note that the line that passes through the star and connects the nearest and farthest points of the planet's orbit is called the major axis, and half this line is the semimajor axis — which we consider the planet's average distance from the star.

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? A. just after sunset. B. just before dawn. C. midnight. D. at noon.

D. at noon. Correct. 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.

When would you expect to see Venus high in the sky at midnight? A. in its full phase B. in its waning crescent phase C. in its waxing crescent phase D. in its waxing gibbous phase E. never

E. never. Correct. For Venus to be high in the sky at midnight, it would have to be on the opposite side of our sky from the Sun. But that never occurs because Venus is closer than Earth to the Sun.

Process of Science: Identifying Falsifiable Statements Learning Goal: To understand what we mean by a "falsifiable" claim. Introduction. A scientific model must make predictions that can be tested by observations or experiments. One way you can decide whether a claim can be tested is to first decide whether it is falsifiable, meaning that it could potentially be proven false. As a simple example, the statement "All sharks are gray" is falsifiable because it could be proven false by the discovery of a white shark.

Let's start with an example from history. Listed below are a series of claims regarding United States President John F. Kennedy (1917-1963). Classify each statement according to whether or not it is falsifiable.

Earth orbits in the shape of a/an _____ around the Sun.

ellipse

According to Kepler's second law, Pluto will be traveling fastest around the Sun when at _____.

perihelion

The mathematical form of Kepler's third law measures the period in years and the semimajor _____ in astronomical units (AU).

semimajor axis

What is neither model?

we sometimes see a crescent Jupiter.