ASTR 100 - Hmk 4

He discovered that the orbits of planets are ellipses. (a) Copernicus (b) Kepler (c) Tycho Brahe (d) Galileo (e) Ptolemy

(b) Kepler

Which of the following orbits has the largest semimajor axis? (a) Planet orbit shown as a highly-flattened ellipse with the Sun at one focus. Minor axis is the same as other ellipses. (b) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at one focus. Minor axis is the same as other ellipses. (c) Planet orbit shown as a slightly non-circular ellipse with the Sun at one focus. Minor axis is the same as other ellipses. (d) Planet orbit shown as perfect circle with Sun at center. Radius is same as minor axis of elllipses.

(b) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at one focus. Minor axis is the same as other ellipses. (The semimajor axis is half of the distance across the ellipse in its longest direction (which means half of the major axis), which is also the planet's average distance from the Sun. Therefore, the ellipse that measures the longest across is the one with the largest semimajor axis.)

Which of the following paths could not be a real orbit for a planet around the Sun? (a) Planet orbit shown as a slightly non-circular ellipse with the Sun at one focus. Minor axis is the same as other ellipses. (b) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at precise center of the ellipse. Minor axis is the same as other ellipses. (c)Planet orbit shown as perfect circle with Sun at center. Radius is same as minor axis of elllipses. (d) Planet orbit shown as a highly-flattened ellipse with the Sun at one focus. Minor axis is the same as other ellipses. (e) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at one focus. Minor axis is the same as other ellipses.

(b) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at precise center of the ellipse. Minor axis is the same as other ellipses. (Kepler's first law tells us that the orbit of a planet 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. [Note that the circular path is allowed because a circle is an ellipse in which both foci are at the center.])

All of the following statements are true. Which one can be explained by Kepler's third law? (a) Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun. (b) Venus orbits the Sun at a faster orbital speed than Earth. (c) The Sun is not in the precise center of Saturn's orbit. (d) All the planets orbit the Sun in nearly the same plane. (e) Earth is slightly closer to the Sun in January than in July.

(b) Venus orbits the Sun at a faster orbital speed than Earth. (Kepler's third law can be stated as the precise mathematical relationship p^2=a^3; (where p is the planet's orbital period in years and a is its average orbital distance in AU). The essence of the law, however, is that it means planets closer to the Sun orbit at faster average speeds than planets farther from the Sun. Therefore, Venus orbits at a faster orbital speed than Earth, because Venus is closer to the Sun.)

In science, a broad idea that has been repeatedly verified so as to give scientists great confidence that it represents reality is called _________. (a) a paradigm (b) a theory (c) a Ptolemaic model (d) a hypothesis

(b) a theory

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? (a) The area swept out in July is larger. (b) The area swept out in January is larger. (c) Both areas are the same.

(c) Both areas are the same. (Kepler's second law tells us that a planet always sweeps out equal areas in equal times. Therefore, Earth sweeps out the same area in any 31-day period, no matter what month it is.)

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) It is summer in January and winter in July. (c) Earth travels faster in its orbit around the Sun in January than in July.

(c) Earth travels faster in its orbit around the Sun in January than in July.

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) All the planets have nearly circular orbits. (c) Jupiter orbits the Sun at a faster speed than Saturn.

(c) Jupiter orbits the Sun at a faster speed than Saturn.

Which of the following orbits is the most eccentric? (a) Planet orbit shown as perfect circle with Sun at center. Radius is same as minor axis of elllipses. (b) Planet orbit shown as a slightly non-circular ellipse with the Sun at one focus. Minor axis is the same as other ellipses. (c) Planet orbit shown as a highly-flattened ellipse with the Sun at one focus. Minor axis is the same as other ellipses. (d) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at one focus. Minor axis is the same as other ellipses.

(c) Planet orbit shown as a highly-flattened ellipse with the Sun at one focus. Minor axis is the same as other ellipses. (Eccentricity is a measure of how "stretched out" an ellipse is. A perfect circle has zero eccentricity, and the most stretched out ellipse has the largest eccentricity.)

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

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

Which of the following orbits shows the planet at aphelion? (a) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at one focus. Minor axis is the same as other ellipses. The planet is at the point furthest from the Sun. (b) Planet orbit shown as a slightly non-circular ellipse with the Sun at one focus. Minor axis is the same as other ellipses. The planet is at the point of closet approach to the Sun. (c) Planet orbit shown as a highly-flattened ellipse with the Sun at one focus. Minor axis is the same as other ellipses. The planet is at a point in the orbit along the semi-minor axis.

(a) Planet orbit shown as a moderately-flattened ellipse slightly wider than the others with the Sun at one focus. Minor axis is the same as other ellipses. The planet is at the point furthest from the Sun. (Aphelion is the point in a planet's orbit that is farthest from the Sun.)

Which of the following statements about an ellipse is NOT true? (a) The focus of an ellipse is always located precisely at the center of the ellipse. (b) A circle is considered to be a special type of ellipse. (c) An ellipse with a large eccentricity looks much more elongated (stretched out) than an ellipse with a small eccentricity. (d) The semimajor axis of an ellipse is half the length of the longest line that you can draw across an ellipse.

(a) The focus of an ellipse is always located precisely at the center of the ellipse.

What do we mean by a geocentric model of the universe? (a) a model of the Milky Way Galaxy that has our solar system located at its center (b) a model designed to explain what we see in the sky while having Earth orbit the Sun (c) a model designed to explain what we see in the sky while having Earth located in the center of the universe (d) the name given to sphere-shaped models that show all the constellations as they appear in our sky on the celestial sphere

(c) a model designed to explain what we see in the sky while having Earth located in the center of the universe

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.

Based on the video, which Venus phase would be impossible to see (from Earth) if Venus orbited Earth as described in Ptolemy's Earth-centered model? (a) crescent on the right side (b) new (c) gibbous (nearly full) (d) crescent on the left side

(c) gibbous (nearly full) (Phases that show more than a crescent are not possible in Ptolemy's Earth-centered model, so a gibbous or full Venus could never occur if Venus orbited Earth.)

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.

What is meant by Occam's Razor? (a) a poorly designed experiment that fails to show the difference between two competing theories (b) the fine line between science and pseudoscience (c) the idea that scientists should prefer the simpler of two models that agree equally well with observations (d) a well-designed experiment that clearly shows the differences between two competing theories (e) the shaving implement of a medieval scholar

(c) the idea that scientists should prefer the simpler of two models that agree equally well with observations

From Kepler's third law, an asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to (a) 8 astronomical units. (b) 16 astronomical units. (c) 2 astronomical units. (d) 4 astronomical units. (e) It depends on the asteroid's mass.

(d) 4 astronomical units.

Which of the following statements about scientific models is true? (a) All current models are correct. (b) A model tries to represent all aspects of nature. (c) A model tries to represent only one aspect of nature. (d) A model can be used to explain and predict real phenomena. (e) All models that explain nature well are correct.

(d) A model can be used to explain and predict real phenomena.

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? (a) Copernicus placed the planets in the wrong order going outward from the Sun. (b) Copernicus misjudged the speeds at which the planets orbit the Sun. (c) Copernicus misjudged the distances between the planets. (d) Copernicus used perfect circles for the orbits of the planets, whereas planets actually have elliptical orbits. (e) Copernicus placed the Sun at the center but did not realize that the Moon orbits Earth.

(d) Copernicus used perfect circles for the orbits of the planets, whereas planets

He developed a system for predicting planetary positions that remained in use for some 1,500 years. (a) Galileo (b) Copernicus (c) Tycho Brahe (d) Ptolemy (e) Kepler

(d) Ptolemy

What is meant by a hypothesis? (a) a tentative understanding of a natural phenomenon (b) a historical theory that has been proved inaccurate (c) a natural phenomenon that requires explanation (d) an explanation for a phenomenon that makes a prediction (e) a pseudoscientific idea

(d) an explanation for a phenomenon that makes a prediction

The great contribution of Tycho Brahe was to _________. (a) discover four moons orbiting Jupiter, thereby lending strong support to the idea that Earth is not the center of the universe (b) offer the first detailed model of a Sun-centered solar system, thereby beginning the process of overturning the Earth-centered model of the Greeks (c) discover that planets orbit the Sun in elliptical orbits with varying speed (d) observe planetary positions with sufficient accuracy so that Kepler could later use the data to discover the laws of planetary motion

(d) observe planetary positions with sufficient accuracy so that Kepler could later use the data to discover the laws of planetary motion

All of the following statements are true. Which one can be explained by Kepler's second law? (a) Venus orbits the Sun at a faster orbital speed than Earth. (b) All the planets orbit the Sun in nearly the same plane. (c) The Sun is not in the precise center of Saturn's orbit. (d) Earth is slightly closer to the Sun in January than in July. (e) Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun.

(e) Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun. (Kepler's second law tells us that a planet moves faster in its orbit when it is closer to the Sun (near perihelion) than when it is farther (near aphelion). This law applies to all planets and therefore explains the statement about Mars.)

Kepler's second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, means that (a) the period of a planet does not depend on its mass. (b) planets that are farther from the Sun move at slower average speeds than nearer planets. (c) planets have circular orbits. (d) a planet's period does not depend on the eccentricity of its orbit. (e) a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.

(e) a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.

When did Copernicus live? (a) about 5000 years ago (b) about 100 years ago (c) about 1000 years ago (d) about 2000 years ago (e) about 500 years ago

(e) about 500 years ago

What is an ellipse? Define its foci, semimajor axis, and eccentricity.

1) An ellipse is an oval-like figure. We can draw an ellipse by putting two tacks down into a piece of paper and then running a loop of string around both of them. If we hook a pencil inside the string, pull the loop tight, and then drag the pencil around, keeping the string taut, we get our ellipse. 2) The foci of the ellipse are the locations of the tacks. 3) The semimajor axis is half the length of the ellipse along its longest axis. 4) The eccentricity is a measure of how noncircular the ellipse is: zero eccentricity is a circle, while higher values of the eccentricity make more stretchedout ellipses. (The maximum value of eccentricity for an ellipse is 1.)

Each of the four diagrams below represents the orbit of the same comet, but each one shows the comet passing through a different segment of its orbit around the Sun. During each segment, a line drawn from the Sun to the comet sweeps out a triangular-shaped, shaded area. Assume that all the shaded regions have exactly the same area. Rank the segments of the comet's orbit from left to right based on the length of time it takes the comet to move from Point 1 to Point 2, 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.

Although Kepler wrote his laws specifically to describe the orbits of the planets around the Sun, they apply more generally. Kepler's second law tells us that as an object moves around its orbit, it sweeps out equal areas in equal times. Because all the areas shown here are equal, the time it takes the comet to travel each segment must also be the same.

(True/False) Copernicus's model of the solar system gave much better predictions than the model of Ptolemy.

False

(True/False) The Ptolemaic model of the solar system was useless for predicting planetary positions.

False

Consider again the diagrams from Parts D and E, which are repeated here. Again, imagine that you observed the asteroid as it traveled for one week, starting from each of the positions shown. This time, rank the positions (A-D) from left to right based on how fast the asteroid is moving at each position, 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.

Fastest to Slowest: 1) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is at its perihelion. It revolves clockwise. 2) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is located in the bottom right quarter of the orbit. It revolves clockwise. 3) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is located in the top left quarter of the orbit. It revolves clockwise. 4) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is at its aphelion. It revolves clockwise. (Just as you found for the comet in Parts A through C, the asteroid must be traveling at a higher speed during parts of its orbit in which it is closer to the Sun than during parts of its orbit in which it is farther away. You should now see the essence of Kepler's second law: Although the precise mathematical statement tells us that an object sweeps out equal areas in equal times, the key meaning lies in the idea that an object's orbital speed is faster when nearer to the Sun and slower when farther away. This idea explains why, for example, Earth moves faster in its orbit when it is near perihelion [its closest point to the Sun] in January than it does near aphelion [its farthest point from the Sun] in July.)

Each of the four diagrams below represents the orbit of the same asteroid, but each one shows it in a different position along its orbit of the Sun. Imagine that you observed the asteroid as it traveled for one week, starting from each of the positions shown. Rank the positions based on the area that would be swept out by a line drawn between the Sun and the asteroid during the one-week period, from largest to smallest. 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.

Kepler's second law tells us that the asteroid will sweep out equal areas in equal time intervals. Therefore, the area swept out in any one week period must always be the same, regardless of the asteroid's location in its orbit around the Sun.

Assume that all the shaded areas have exactly the same area. This time, rank the segments of the comet's orbit from left to right based on the distance the comet travels when moving from Point 1 to Point 2, 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.

Kepler's second law tells us that the comet sweeps out equal areas in equal times. Because the area triangle is shorter and squatter for the segments nearer to the Sun, the distance must be greater for these segments in order for all the areas to be the same.

Imagine that you observed the asteroid as it traveled for one week, starting from each of the positions shown. This time, rank the positions based on the distance the asteroid will travel during a one-week period when passing through each location, from longest to shortest.

Longest to shortest: 1) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is at its perihelion. It revolves clockwise. 2) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is located in the bottom right quarter of the orbit. It revolves clockwise. 3) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is located in the top left quarter of the orbit. It revolves clockwise. 4) an elliptic orbit with the vertical major axis and the Sun in its lower focus. An asteroid is at its aphelion. It revolves clockwise. (Kepler's second law tells us any object will sweep out equal areas in equal times as it orbits the Sun, which means the area triangles are shorter and squatter when the object is nearer to the Sun, so that the object covers a greater distance during any particular time period when it is closer to the Sun than when it is farther away.)

Describe an example of pseudoscience (at least 2 sentences). Describe why is it considered pseudoscience, BE VERY specific! (at least 2 sentences)

One example of pseudoscience is ufology. This is considered the study of unidentified flying objects. Ufology is considered pseudoscience, because ufologists continue to claim it to be science despite the fact that the science community disagrees. Another reason is that ufology does not have supporting evidence.

Assume that all the shaded areas have exactly the same area. This time, rank the segments of the comet's orbit based on the speed with which the comet moves when traveling from Point 1 to Point 2, 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.

The comet takes the same time to cover each of the four segments shown, but that it travels greater distances in the segments that are closer to the Sun. Therefore, its speed must also be faster when it is closer to the Sun. In other words, the fact that that the comet sweeps out equal areas in equal times implies that its orbital speed is faster when it is nearer to the Sun and slower when it is farther away.

(True/False) Process of Science: If any single test of a scientific hypothesis contradicts it, the hypothesis must be revised. (Assume that you've ruled out errors in the testing process; that is, the test result really does contradict the hypothesis.)

True

(True/False) Scientific theories can never be proved true beyond all doubt.

True

What is pseudoscience?

a claim, belief or practice which is presented as scientific, but which does not follow the scientific method